Rough Idle Update on 300TE....I'm totally out of ideas - Page 3 - PeachParts Mercedes-Benz Forum

JonL · #1 04-09-2009, 01:10 AM

Quote:

Originally Posted by ps2cho

Thank you.

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?

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.

Chowbow · #2 04-08-2009, 05:39 PM

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.

JonL · #3 04-08-2009, 05:45 PM

Very good suggestion... EGR valve sticking.

pawoSD · #4 04-08-2009, 05:56 PM

He has an '88, no EGR valve.

Ivanerrol · #5 04-08-2009, 09:15 PM

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.

pawoSD · #6 04-08-2009, 09:48 PM

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?

pawoSD · #7 04-09-2009, 01:14 AM

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.....

ps2cho · #8 04-09-2009, 01:33 AM

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?

Quote:

Originally Posted by JonL

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.

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

pawoSD · #9 04-09-2009, 01:44 AM

Quote:

Originally Posted by ps2cho

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.

tinypanzer · #10 04-09-2009, 07:14 PM

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.

slk230red · #11 04-09-2009, 07:35 PM

Quote:

Originally Posted by tinypanzer

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

david s poole · #12 04-09-2009, 08:13 PM

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].

ps2cho · #13 06-07-2009, 02:06 PM

After driving the 260E for a month while the ignition tumbler was being replaced in the wagon...its easier to see what is going on.

It is very clear that the erratic vacuum begins when the car enters closed loop after being cold. I think my next course of action would be to replace the entire CIS fuel system with the spare I have and see what happens. With that, it will be the potentiometer, fuel distributor and eha. As was said above, maybe even though the potentiometer checks out, it could have a dead spot or something.

My second question -- If the timing is in fact within spec, can I rule off the crank pos sensor and hall sensor? Or could they still be potential problems?

Can anybody also explain to me how the hall sensor affects the CIS? Does it even affect the CIS? Whatever is causing this the rough idle is making massive overfueling and killing my power at the bottom end.

Madd78 · #14 11-29-2009, 03:05 PM

ps2cho,

I have a 88 300TE, and went the same route. Concentrate on the potentiometer/air flow sensor. My sensor would do the same thing when it got warm, sometimes it would read off the correct reading, and sometimes not. (pins 1 & 2 .65v then intermittently to 1.01v - 1.04v)

This would be my second sensor that i've installed in the car in 2 years. First year the rpm gauge was sporadic(dead giveaway), second year(day before thanks giving 09') started to do what yours did in the video with the economy and rpm's,and later on my rpm's/idle got sporadic car started to die on occasion at stop lights or to turn.

Replaced mine, and set it to .65 and it runs great.

ps2cho · #15 11-29-2009, 04:27 PM

Awesome thanks! I will grab 2-3 at the junkyard and give it a try...I have tested mine, but its about the only item I have not replaced so its worth a shot!