Rough Idle Update on 300TE....I'm totally out of ideas
 

How it drives:
Idles rough, but as soon as you touch the throttle it disappears. Performance is slower than should be (iWrock has driven my car). Can't feel any misfiring when accelerating...its all at idle.

Static Tests:
-Throttle Plate adjusted + centered correctly.
-Fuel Pressure perfect (5.4bar 4.9bar + holds 3bar after 30mins on specs)
-Airflow Potentiometer reads .7v, dead on specs.
-No error codes
-No vacuum leaks
-Mixture tried/set all different configurations. Settled with 50%
-Compression perfect.
-EZL reads 85% engine off ignition on. WOT reads 20%
-I get ~15MPG average so fuel economy lower than it should be. With 140miles Freeway, 30miles City I get 17MPG.
-Slower than the car should be performance-wise

Parts swapped/replaced:
New OVP
New Coolant Temperature Sensor
New Voltage Regulator
New Injector's+Seals
New Non-Resistor H9DCO's Spark Plugs
New Ignition Wires (checked for arching as well)
New Distributor Rotor + Cap
New Fuel Filter
New Breather Hoses
New Ignition Coil
New O2 sensor
New Motor Mounts
New Head gasket + valve job -- Compression 190psi across the board.
Swapped Jetronic Brain /w used one
Swapped Fuel Pump Relay /w used one
Swapped Cold Start Valve /w used one (in case it was leaking)
Swapped EZL /w used one

I don't understand why I still have this rough idle :confused:
Many of you have helped me through this and a lot of the things I have replaced were bad/old or improved the engine in some way or another so I don't feel bad spending the money...I just want my smooth idle!!

I don't know if there any more static tests I can do on this? Honestly what the hell is left that could be causing this??

Not sure where to go from here....:mad:

I don't know if I should just take it to the dealership? I'm afraid they wont find anything as I have gone over much of the stuff they will check for...?

Can I rule off the fuel distributor if the fuel pressure is okay?

A few pictures so you can see cleanliness and general condition of engine.

http://www.ps2cho.net/downloads/phot...ket/head_4.jpg
http://www.ps2cho.net/downloads/phot...t/rebuild2.jpg
http://www.ps2cho.net/downloads/phot...t/rebuild1.jpg
http://www.ps2cho.net/downloads/phot...ttle_body1.jpg

Personally I'd probably try swapping a different fuel distributor on just for the heck of it....who knows, maybe yours has some weird internal issue that's causing it to not meter the fuel properly.

I've noticed that my M103 idles "rough" sometimes, and by rough I mean you can tell its idling, but its not misfiring (I've experienced that).....but at other times (most of the time) its so smooth you can't tell its running. Mine seems to get about 18.5-20mpg even with me being a leadfoot.....

I am being picky when I say it feels "rough".....my sister's van and my uncles cavalier engines both vibrate "in general" when idling.....by comparison the M103 runs like a fine watch....with a slight vibration sometimes.

Is the vibration strong? Or just enough to be annoying?

Have you considered trying...dun dun dun....Resistor spark plugs? I ran mine on the H9DCO plugs, and it ran like crap....well, it ran great for 50 miles, then it lost about 2 cylinders and ran horrible....got 11mpg and had no power. I quickly replaced them with NGK resistor plugs, and it has run beautifully since....and that was quite a while ago. When I took out the non-resistors....they were totally coked.

I noticed you've not replaced the fuel pump. Is it possible that it might be tired?

I've had one like that, tried everthing, never could rid of it. Some people told me that's just what 103 motors do - idle rough when they get old, built into its DNA. But you don't have that many miles. Cam wear is another theory, but that shouldn't be on that mileage.

Cam has zero wear on it at all along with the pistons and valves etc...Looks pretty brand new inside there.

I'll swap the fuel distributor...I have a couple in my random parts box.
Wouldn't it show as a fuel pressure problem though if it was bad?

I might try the NGK resistor plugs for the hell of it. Got a part # for them? Are they easy to find at a local pepboys/autozone or will I have to order online? I believe there is an NGK warehouse in Irvine, CA close to where I live...maybe they sell them there too...
I've pretty much used the H9DC0's since I got the car because I read they are the OEM recommended set.

The rough idle isn't a strong one anymore, but its enough to be annoying. It is pretty inconsistent...some days can't feel it AT ALL...other days I can. Either way I get horrible MPG and a lack of power.

Of course pulling the Fuel distributor on and off the AFM will require a new o ring between them and the levels and adjustments made to spec.

Tried an EHA or adjustment of yet?

Your pictures of the head valve train look impressive.

What does your vacuum gauge look like at idle when warm?

Check your purge valve if it is leaking in outside air & might want to change out the camshaft position sensor.

As long as you're down to the "I'll try anything" stage, take a look at the routing of the ignition wire between distributor and coil. Mine was laying up against the hot thermostat/waterpump. I rerouted it so it now runs across the intake manifold instead, and stays cooler. I have no idea what the factory routing was, but that improved my idle considerably. That, despite no outwardly visible signs of damage to the wire insulation. Go figure.

i've experienced BAD new injectors, bad spray patterns at idle

motor mounts might need changing if you feel a distinct difference
betwee idle in park/drive/reverse

a'

I have tried 2 different EHA's from the junkyard.
Vacuum gauge at idle sits just slightly left of the red line. With AC on it sits dead on the first part of the red. I've replaced every vacuum hose and had the car smoke tested for leaks.
It moves slightly of course with the rough idle from the rpm's going up and down slightly/mixture adjusting itself.

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The 1988 model does not have a purge valve.

I tested the resistance on the CPS and it checked out...but I have read that on one hand its a "hit or miss", but other people have reported funky things...so I am not sure.

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Ignition coil wire is fine...I've tried two different brand new set of ignition wires.

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Brand new injectors as of 2 weeks ago.

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Its an actual engine rough idle, not bad mounts. I swapped the mounts either way.
Something is killing my power and my fuel economy slightly.

try this idle engine in drive with emergency brake on.grab 12mm wrench and open the fuel lines at the fuel distrib one at a time to see which one makes the least difference to the running.it helps to have a vacuum gauge under the hood when doing this.what i suspect is that your fuel distr is not providing enough fuel at idle on one cylinder.my 420 with exact same setup only 8cyl is doing the same thing.i can mask it almost completely by running the a/c at idle and loading the motor.

My CPS tested in spec.....but it caused the car to stall in traffic and throw a code 7....(Engine RPM fault)

With a new one it has run perfectly.....never stalled since, not even once.

I'll give it a try although I think it will be very difficult to tell as the engine is alot smoother these days. I have two other fuel distributors that I can test. Maybe I will start with that first and see if it makes any difference.

What do you mean by a vacuum gauge under the hood?

I read somewhere that these fuel distributors can be cleaned by yourself...Is this true? I'll shoot some carb cleaner all through the one I have...but what about taking it apart?

I don't know if the fuel distributor can be cleaned like that by a home user....its quite complex inside.

I clean mine by running lots of Redline SI-1 through it. :D

The NGK spark plugs I am using I found on europartsdirect.com...just look up your car and under the spark plugs section they have one type of NGK available....that is what I am using currently and they work really well.

Here's a pic of it:

http://12.153.160.115/webapp/wcs/sto...s/full/TR5.jpg

Thanks I'll order a set.

Found the rebuild. It is pretty interesting. I might give it a shot seeing as I have two distributors laying around.

www.porsche928forums.com/download/manuals/CISRebuild.pdf

Ok I was doing some thinking today...and I read that the vacuum gauge on the instrument cluster attaches to the intake manifold to read the pressure inside.

With that in mind, if my vacuum gauge fluctuates slightly, doesn't that mean that there is not an even, constant amount of air entering the intake manifold at idle?

Does that mean a vacuum leak, or would the airflow plate be moving slightly based on electronic signals from elsewhere? What are your thoughts on this?
I have gone through every single hose on that engine...All the idle air hoses, all the ones that attach to the intake manifold and the one under the KE mixture unit.

If it is moving around when the engine is idling I'd say there is a leak. Mine is stone steady at idle, especially when in drive.

Fluctuations would point to a leak somewhere....

Does the o-ring on the top of the dipstick seal well? That is an overlooked vac leak source....I found mine to be flat and not sealing well.

I just don't get where....
Maybe I need to get it smoke tested again.

Yeah it seals well...why would that be a vacuum leak though? It doesn't affect pressure in the intake manifold.

Is there a way to test the air pressure in the intake manifold with a gauge? Is there a spec I can check it against?

You must have a leak somewhere.

At idle with a warm engine and in neutral the vacuum gauge on my 260e sits at zero - the opposite of the red. With drive engaged it sits slightly off into the main section. Stationary in drive with the AC on, the needle sits about 3/4 to the top - nowhere near the red section.

Get a stand alone vacuum gauge. Go under the bonnet. Disconnect every vacuum line (including the large one for the brake assist) and block the exits off. Connect the external vacuum gauge to one of the outlets. Start eliminating leaks by connecting each vacuum outlet in turn.

Other suspects. The vacuum levels the lights - you may have a leak in one of them or the control switch near the light switch. The heater controls are by vacuum sometimes a controller is suspect and leaks vacuum. Make sure the AFM rubber is leak proof. Make sure the one way valves to the Brake are good. etc etc etc.

A warped valve cover can also cause a problem - even with a new gasket. Does it leak oil? How about the oil filler cap? Tight and the gasket in it good?

The Air fuel mixture must be spot on. The air damper in the AFM set at the correct level.

As mentioned above. The oil level stick has a gasket top and bottom.

With the engine on and car in idle. Can you hear a hissing sound in the interior of the car anywhere? Quite garage and no audio system on for this test.

Have you checked your exhaust for restriction? Bad cat, bad resonator, bad muffler...high back pressure could be causing this...especially as you are seeing lack of power at higher rpm's and bad fuel mileage....Can check short term by removing the O2 sensor to let exhaust escape with less restriction..if performance improves perceptively...you have a pretty good idea.

I only have a lack of power at idle and I have had the cat replaced. I'll unplug the O2 sensor and see what happens.

Thanks.

The US spec cars do not have the vacuum adjustable headlamps.

See my remarks earlier today about cleaning the O2 sensor connector:
http://www.peachparts.com/shopforum/tech-help/55330-water-floor-cure-w124s.html

No hissing sounds. No oil leaks. I have followed the DIY on vacuum detection using the O2 sensor voltage as the meter in the past and didn't find any changes when reconnecting all the vacuum elements.

At idle in drive, it sits just slightly left of the start of red. With A/C on, it sits dead on the very start of red.

The oil filler cap is leaking slightly though...but realistically is that going to really kill my MPG and power...this much? Is there a gasket that goes around the filler hole?

I found a very nice looking valve cover at the junkyard...even better than my one which still looks great. Maybe I'll swap it over to solve the leak?

Hardly ever rains in CA, and my foot wells are fine.

I was referring specifically to the O2 sensor connectors -- to be sure they are secure and not corroded.

But you said you have slower performance... how would you even know if you only have a lack of power at idle? At idle you are using no power!

OK, I don't know your model in particular, but I've been a mechanic in a previous life and I'm a mechanical engineer in the engine development business... so I'll stick in my .02.

Idle vacuum should be very high. It sounds like yours is low. The fluctuation I wouldn't worry about just yet... if the engine is idling poorly, the fluctuating idle speed will cause a fluctuating vacuum reading. Low vacuum... it isn't because of a leak (although you might still have one). It's because the engine is idling with more throttle than it should require. It's doing this to take in more air and fuel because it is running inefficiently. Why is it running inefficiently? That will be the key to solving everything. Possibilities:
Incorrect A:F ratio. Probably not, because you've got on O2 sensor, no fault codes, and you've been through the fuel system. Still could be a subtle cause like bad intake valve guides, or a faulty PCV system (that's why someone posted about the dipstick and oil cap). Possibly something with the evaporative emission system, but I have no clue how that works on your car.
Exhaust restriction. You say you have checked the cat, also it would manifest more as running out of power with a slight lag as you accelerate.
Retarded or erratic ignition timing. I haven't seen that you've checked this. Put a timing light on it, see where it is at idle. See if it is stable. See if it advances sharply and cleanly when the engine is revved up. Erratic and retarded timing would cause all your problems.
Poor compression. Your engine looks beautiful. It could still have screwed up cam timing which is essentially like having poor compression. Especially possible because the system has obviously been molested. (No reflection on your mechanical capabilities, but a realization that something that has been touched is more likely to have a problem.) Retrace your steps. Why was the head off? Are any of your valves bent or sticking? Weak or broken valve springs? Tight valves anyplace? Bad hydraulic tappet(s) making a valve stay open?

That doesn't sound right for the economy gauge, in drive mine sits in the black just off being all the way to the left, in Park its all the way to the left, in drive with A/C on it only moves slightly, but still way into the black....nowhere near the red zone.

Shot in the dark... I'm wondering if your car has an EGR valve? If it's bad it could cause some idling issues. I haven't heard you mention that in the past and no codes should mean that it's OK, but you've done just about everything else. I'm not the expert but if there's a way that you can at least bypass it for now or test one from the junkyard, it may be one of those not-too-difficult things to try.

Very good suggestion... EGR valve sticking.

He has an '88, no EGR valve.

M103 engine ignition timing is all CPU and sensor controlled. MB sets up the timing for the US based on the fuel octane, quality and emission controls.

Thank you.

I have low power at the bottom end, I didn't mean idle, sorry. Along with very poor MPG. My last fillup was 12.1mpg.

To this post and others, the 1988 model does not have an EGR valve.
Compression is 190psi all cylinders.

I had the entire head rebuilt including new valve guides + seals. Head pressure tested and skimmed. I had the head off because I was losing a lot of oil and coolant and was told by a local indy that the head gasket was leaking. It was a great opportunity to really get to know the engine (my first rebuild) and it didn't cost me a whole lot. Experience was well worth it. Had some help from my dad of course...but he is stumped on the rough idle too. He goes by "Merky" on this forum, but rarely posts. There were a few other items such as the water pump that needed replacing. The valves looked great.
I have a large thread with tons of pictures that I took throughout the whole thing here:
http://www.peachparts.com/shopforum/tech-help/241701-my-300te-head-gasket-thread-yes-pics.html

When I rebuilt the top end, I set the cam timing as it shows in the MB manual to perfection. Should I need to get a light to still check it?

EDIT: Here is a video on youtube
http://www.youtube.com/watch?v=kMAVAjyVSTE
You can see the idle economy gauge and rpm fluctuations. Maybe this will give you some ideas.

I would love to take it to the dealer and have it fixed....but I A) expect a huge bill B) Expect several expensive items to be fixed before the real solution is found :(

Interesting in the video. It really does look like either the idle control valve is fluctuating/hunting........possibly due to the Air Flow Potentiometer not being in spec......or there's a bad vacuum leak somewhere.

12.1 Mpg would point to massive overfueling.....does the exhaust smell like it? Is it clean? I wonder if the timing might be slightly off somehow?

No guarantee taking it to a dealer will be any good. The local M.B. factory operated stealerships near me have "technicians" instead of mechanics. Many of these technicians are not much older than my M103 engine. They are all geared up to operate on the computer controls of the newer models. - The diagnose and replace system.
When I need advice from them (extremely rarely) they need to call their "old guy" or do a search from their on line manuals. Sometimes they even point me in the direction of an indie specialist - often an old dealership mechanic out on his own.

You would need to find an Indie specialist.

For injection problems I take my cars to a franchise Bosch injection specialist. Even the dealerships send their cars to these guys.

I see that Wagon has Euro headlights. Are these not converted to level control?

Not usually....my dad's car has euros without the level control as well....

I take it back, he does not have them "without" level control, the level control hookups are present, but it is not used. Someone just put little stubs of plugged vacuum line on them to keep dirt out. They are true Bosch Euros...

It is clean, yes...but as for the smell...I have a brand new cat in there so that's hard to tell...
I checked the AFP with a DMM and it showed .7v which is on spec. I have replaced every idle air hose in the engine...I just don't get it :confused:
I have sprayed carb cleaner all over the engine at every hose and it makes no change.

Is there a way to check for crankcase pressure? Is there a spec for it or something?

That's what I have read from a number of people.
I took the car to a specialist in Tarzana "Enrique"...and he replaced a hose that he said was leaking and said the car was perfect. It was far from it when I got it back...It was horribly slow and still had a rough idle. He must have adjusted the EHA because I had to turn it richer to get the lost power back. It was horrendously slow. I won't take it back to him again that's for sure.

They are just DEPO Euros. I have not done any conversions. The stock lights didn't have it either.

I wonder if a whole new air meter/distributor assembly off of another car would make it run any different. Then you'd be swapping the air meter, Potentiometer, EHA, and Fuel distributor/pressure regulator all at the same time.

I have one...so I could. The potentiometer wire is cut off though. Got it one day at the junkyard and went the checkout window with the female who looked new....Charged me like $25 for the whole thing ;)

...but I'd really like to figure out WHY there is an uneven flow of air in the intake manifold. It shouldn't be fluctuating like that...it should be rock steady, right?

But for reference, I have swapped the EHA, fuel pressure regulator, and fuel distributor before....

The light is to check ignition timing, and yes you should do it. I realize that it is all set by computer, but there may be a problem in the ignition timing nonetheless. If you find that the timing is off, then you know what systems to start chasing. Things like crank position sensor, cam position sensor (if present), knock sensor, temp sensors, etc.

Does the air meter move smoothly? On my 300E it was crooked and got stuck in the opening when coming back to the rest position.

I think that the Potentiometer is more likely to cause a hunting idle syndrome than the EHA.....

Yes. The picture in the first post shows the whole mixture unit removed. I adjusted the sensor plate so its perfect.

Even if the potentiometer checks out voltage-wise...could it still be bad?

Gotcha. That will be first thing to do from now.

Even if it tests in spec with the car off, that doesn't tell you if its in good shape in a linear way.....I learned from a great mechanic local to me that the only way to truly test the Potentiometer is with an analog voltage meter, so you can see if the voltage change is perfectly linear. A digital meter has too slow a refresh rate to display accurate changes in the voltage.

If the computer is trying to adjust the idle with the idle control valve but the Potentiometer has a bad spot on it around idle, it will confuse the computer and cause it to keep adjusting the valve back and forth trying to find a good idle.

Yes, you would need to check that with an analog meter for best results. Digital meters won't show dead spots, dips, or other non-linearities nearly as well as a needle meter.

Forgive me if you've already answered this question but, have you checked to make sure it's running in closed-loop?

Also - Somebody posted a link to a PDF file with a complete theoretical description and diagrams of the Bosch CIS system. It's well worth the read. I think the post is maybe a month old? I highly recommend checking it out.

Is this the link?

http://clubgtinorfolk.com/downloads/Information/boschtech-12d.pdf

if i remember correctly there was a tsb by mercedes concerning a way to raise the idle speed by 50 rpm to handle your issue.you need to cut into the wiring at the ecu and find the purple wire.then scrape off the insulation at one point and attatch a wire which you take to ground[one of the brown wires in that same loom].

Great link thanks.
I know the rough idea of what closed-loop means...but I am not sure how I exactly "tell" that I am in closed-loop.

This is not just a low rpm issue unfortunately.

Monitor the output of the oxygen sensor with a high impedance voltmeter and when the output starts switching between approx. .2 volts and .8 volts you are in closed loop mode.

I know that you changed the o2 sensor but I can't remember exactly what replacement you used. I know that the Volvo 850 that I had was very picky about the sensor. I tried a Bosch universal with no luck and finally installed the Bosch with the OEM connector and all of my problems went away. Also, keep in mind that it is easy to contaminate the sensors with silicone. I have stopped using any RTV that is not sensor safe and no longer use silicone spray to clean up plastic and rubber in the engine bay. I also remember reading that you should not use any type of dielectric grease on the o2 sensor connection.
Good luck.

slk230red - Yup, that's the link. Man, isn't that an awesome read? It really answered a LOT of questions I had about how this type of fuel system works.

Looks like I will have to fig into it this weekend - more than I had hoped.