Trouble when idle / taking off (420 SEL)
 

On my 420 SEL, 230K miles, the car bumbles and shakes a little more than desired when the car is in drive and when I am stopped (like at a traffic light) and when I first hit the gas pedal. The trembling completely goes away after 10 mph.

Usually something like this has happened when I had a bad spark plug. I had all the wires and plugs replaced about 4 months ago for routine maintenance. About 2 weeks ago this trembling started and the mechanic could not figure it out. He replaced all of the spark plugs just to be sure yesterday for $105 and nothing has changed.

The tech's only other idea is the fuel injectors. He "leaned" out the fuel mixture a little bit, according to him, to try a cheap remedy, but it did not work, maybe a tiny bit, but nothing significant.

Does anyone have any ideas? Despite the mileage, the car runs pretty strong. This trembling is annoying and may cause engine damage if I do not address it. My only other option is to take it to a dealer and replace one of the fuel injectors? How to determine what the cause is?

Thanks.

The tech thinks that it could be the "fuel distributor head", something like that. There is a filter in that head which could clog up and the only way to fix it is to replace it which cost $500 just for the part. He said it most likely cannot be anything else.

Any thoughts would be appreciated. :confused: :mad: :confused:

That is a very expensive "could be".
Did you check/clean the idle control valve?
Clean the throtle body?
I would keep searching before I spend $500.00
$105.00 is too much to change sparkplugs.
I would be suspicious of the mechanic.

Thanks. Not sure. My guess is if that is a quick thing I would guess so, but I need to ask. I've been going to him for 5 years, but yeah $105 bucks is steep for changing the plugs. Maybe he added the labor for tweeking the fuel mixture or something.

Normally he has been pretty good, but this time, it has been difficult.

Another suggestion was putting fuel injection cleaner in my gas tank.

That is something I would try, but use Techron.
I was experiencing sort of the same problem, cleaned the Idle control Valve (thoroughly) ran Techron (big bottle) went to Asheville, and problem disappeared. Try to run the Techron right before an oil change.
I see you are at the RTP. I am in Clayton, NC.

I can get to Clayton. Are you a tech or a MB owner? Thanks.

I am an owner, who loves to tinker with cars under a "shade tree"
I can't wait for my job to give me a final placement such that I can buy a house with a 2 car garage. The apartment complex where I reside recently sent me a letter of "encouragent to stop my mechanical practices in the parking lot". HAHA
This was after I decided to change the discs rotors, brake pads, and faulty starter in my trusty Geo Tracker. I had an audience of guys around me trying to learn. It was so funny, they thought that I actually was a mechanic.
There is a member of this forum who works (owns?) in a shop in Raleigh. His name is Joe P - Acme Automotive.
Still, just let me know, and one of these days we can meet to discuss car problems and try to fix them over a few beers.
Are there any other members in the Raleigh area?

The tech really thinks that it is the fuel head (said it had nothing to do with the idle thing). He said that the fuel head replacement can run as high as $1500.

Another option is to try running fuel injector cleaner in the gas tank. Any ideas of what brands work the best?

Any thoughts? Is stevefl still out there?

:(

I'm not sure from your description if your problem is a varying idle speed and the engine stumbling off idle..... or if you simply feel too much vibration or bouncing around of the engine. If the latter, I would first suspect engine mounts having collapsed.

Steve

The tech REALLY THINKS it is the fuel head?, the one that runs between 500 and now 1500?
And the car only stumbles at IDLE, and after 10 mph drives well?
Buddy, time for a second opinion. If the problem is ONLY at low RPM's (idle) I do not think now 1500, on top of 105 to change the sparkplugs is a solution.
We have not even looked at wires, distributor cap and rotor yet.
Fuel filter, air filter when were they changed?
Good point about the motor mounts.
I always go for the cheap fixes first. Clean the ICV, see what happens, clean throttle body, see what happens, change sparkplugs, see what happens, remove dist. cap and rotor-inspect and clean-replace if necessary, see what happens,... and so on.
I get scared when a mechanic tells me:

"I THINK the problem is this..., it is going to cost $$$$$$ to replace it" ....(and let's see what happens)

The motor mounts were checked first thing and it ain't the problem.

Fuel filter, air filter, Wires, distributor, rotor, plugs, etc., was replaced around 3,000 miles ago (~ 3 months ago). The plugs were also replaced yesterday. The throttle thing ain't it.

The problem is how I described earlier. While the car is in drive and at a stop the car trembles and shakes a little due to the engine. It also continues to do that as you lift your foot off the brake and give it gas. The engine runs smooth after 10 mph on up. The idle speed does not taper off nor does it vary significantly. The RPM does bump up and down (when < 10 mph)a little bit during this because the engine is not running right. The tech said that the "fuel head" has a mechanisim in there that is dirty and the only way to fix it is to replace it. "You cannot clean it. "

I have been going to this guy for 5 years and had done great. He said he tried everything, and according to him, he is sure that it is the "fuel head". Let's stop beating him up. I don't think he is trying to pull a fast one, I am just wanting to see if anyone else had similar issues and found something else. Yeah, I might take it to the dealer if the additives don't work.

What I am looking for is input on does anyone know what this $1500 fuel head does? Is it that expensive? Does anyone have any fuel injector brand recommendations other than Techron?

They told me that BG products has a good product and to try that first. I was also thinking, although a long shot, it could be the tank of gas that we last bought could be bad?

Just to clarify. It is not the motor mounts. I can feel that the engine is not running right when < 10 mph. Can the engine get proper fuel when > 10 mph, but not < 10 mph? I don't understand how the fuel head works.

Ok, the only thing that has that price is the fuel distributor @1800.
The second thing I can think of is the air flow meter @600.
Again, let's do the methodical step by step troubleshooting method.
This happens only at slow speed, low RPM.
If it was fuel delivery problem (fuel head=fuel distributor?) I would expect it to be at all times.
Now, partially clogged injector(s) could do this at idle. Faulty ICV, OVP, EHA could also cause the problems you describe.
What I do not understand is what is the fuel head (fuel distributor?)
ICV,OVP and EHA haven't been checked/cleaned? those are relatively cheap, and possible causes for the problems you describe.
I was experiencing similar problems, and cleaning ICV, running Techron and cleaning Throttle Body FIXED my problems (about 8 months ago).
I have found that Techron is the best Injector cleaner.
I hope your problem gets fixed, I have one right now, with the water pump (I think);)

BG 44K is the product you were talking about. I picked some up today.

Thanks. Yeah, I am talking about the fuel distributor. Could the fuel distributor be slightly clogged? Good point about happening at all times. The bumbling goes away after 10 mph. I guess I need to try some cleaner and fresh tank of good gas.

Is the fuel distributor something that can clog or does it just fail completely when it is shot?

The fuel distributor COULD be the problem. When meting out small quantities of fuel at idle, irregularities would tend to show up more than at a high rate of delivery. At idle, the metering slits keep the secondary pressure low enough that rates could vary significantly from injector to injector.

However, there are a lot of other possible causes of your symptoms. We can't know for sure what your tech has done to eliminate other possibilities, but some tests are pretty simple. For instance, to rule out a worn pot in the airflow meter, disconnect the EHA. If idle smoothes out, then the fuel distributor is NOT the issue. Likely the airflow meter pot has a worn spot.

Steve

stumble
 

mattsuzie,
I have had a very similar problem please see thread:
http://www.peachparts.com/shopforum/tech-help/62226-help-please.html
I asked originally if it was the coil got off the topic and rebuilt my entire fuel system no luck, finally replaced the coil. Thats what fixed it. Steveb helpled me alot with the fuel system, I would doubt it is your fuel dist but, I would follow the basic principal and make sure your lambda is working right. BUT first get you ignition checked on a scope, although mine looked okay on the scope it was not perfect and I should have gone with my gut. There are a couple of good people in RTP Joep is on this board. I used to work ar a shop called the Foreign Service owned Dave Pettengill http://www.theforeignservice.com
hope this helps, All I can say spend the time with diagnostics you can throw alot of money at this in parts. I spent a lot of time on it but not too much cash on parts mainly replacing the rubber. The coil was the most expensive part.
good luck
m

EHA SENSOR COULD BE THE COULPRIT
 

pLEASE try the EHA sensor. Messure the voltage at pin 2, it has to be 800 Milivolts +/- 250 milivots. If not, rotate little bit, few degrees till get 800 milivots aproximatly.

It could be burned or broken pins.


See a lot of EHA threaded.

Mario Farias
laprefar@cantv.net

Still no luck. I do not know some of the finite details of what the tech checked. I hate to take it to the dealer though, for the may cost me an arm and a leg , but I guess I have not choice.

Any more ideas?

Ok, so your in RTP and I'm right off 70, one block shy of Duraleigh Rd. Why not drop in and show me exactly what your problem is. Normal fuel head complaints are leakage, skips or bad stumbles. Most bad idles are vacuum leaks, bad/dirty injectors or CO adjustments. However, coils, EZLs and sticking egr valves will also cause 'em. On rare occassions you'll find a M117 with a guide walking in a head causing a intermitent skip and piss poor idle when not skipping. (these are also hard as hell to get a firm diagnosis on)

What I'd like to know is what the base duty cycle readings are and O2 response times. Drop in, we dont bite. :D



Joe

I just had a 300SE experience a poor idle situation and these were the culprits. The mixture was way too lean and indicating around 68% duty cycle. After setting it at around 45% it smoothed right. The tech also did a "carbon clean" which I think is running some BG44K through there. It seems to me that the Bosch CIS FI is a pretty good FI system.

Yeah, its ok. Gotta remember, thats late 60's technology so its a bit rude. CIS-e and its variants are really very simple, reliable systems that give people fits. The main reason is the system works backwards from conventional thinking, higher pressure = leaner mix, lower pressure = richer mix. Drives people mad. :D




Joe

I am running the 44k stuff in it now. The tech also leaned out mixture some. I will see if I can take it to Joe for a look.

Mattsuzie,

Mine had the very same symtoms. It started out with slight shakes/vibrations at idle. As soon as I tapped on the gas, it's glass smooth again. For two years, I've tried (new OEM parts): engine mounts, transmission mount, plugs, cap & rotors, injectors (did try Redline, Chevron cleaners first); and the problem persisted, but worsening over the period. Took it to an independent shop a second time, found that it's indeed the fuel distributor (had previously thought it's the injectors - thus the replacements but they are originals (185K) anyway.)

Bought the re-man. distributor from germanstar.net (less than $500 bucks). Driving it home, all I could say is WOW...

You could check it by loosening each fuel line on the distributor (mine turned out to be no fuel output at all on cyl.#3 at idle - I learned it the hard way).

Hope this helps,
Frank.

Just saw the car. Dead miss off idle, intermitent skip at idle. (like a lean misfire) Popped a plug out, lots of oil for a 2 week old plug. Personally I'm tinking guides but, there are still several other posibilitys. It also has some lifter type noise and more than a few miles on it. I recomended he replace the plugs and see if it clears out for a few days and go from there. Nice guy BTW. :D It just dosen't strike me as a fuel head problem, more like a bad resistor tip or fouled plug. However, the 5.6's I've had with walking giudes have done a remarkable job of mimicing a fouled plug or bad wire.



Joe

I had the same problem.
 

FYI. This is common on these cars. My 560 SEL AMG has had this problem since I got it. I cleaned the ICV, replaced check valves in the pump, then went to the stealership. I have a good repor w/the the head tech who said that Mercedes recommend running one bottle (the big one)of Techron through the system, if there is no change do a second bottle. DO NOT put in three! If you do you will have to replace not only the injectors, but also the fuel head. If this doesn't work then the fuel distributer is gummed up, and will have to be replaced as no mere mortal can rebuild them. I got a used one from Silver Star for $400, off a car that came in wrecked, but running. Fixed the problem in about 20 minutes.

I have the same problem
 

I have the same problem too with my E320. Please read my thread: "New Member Needs Help". Mine started after I cleaned the egr crossover pipe. I think it is vaccum related but can not find a leak. Vaccum leak could affect air/fuel mixture and should affect the idle. But how do you go about checking for vaccum leaks? My model does not have a Throttle valve switch, or whatever they are called.

Interesting that the car starts out completely OK or almost OK for the first 3 miles or so after sitting overnight. Then when the engine is warmed up after about 5 miles the bumbling and stumbling starts. If it was the fuel distributor, does it make sense that after the car sits over night that it improves itself for the first 3 miles the following day?

I only had time to look at 4 of the plugs on one side of the block. The gap was .022" through .032" (pretty tight) - It does not appear that the Tech put the right gap on it. I widened the gap to about .037" on the four. I hope to look at the other 4 over the weekend. After the 44K fuel additive, really not that much change that I can tell.

Had the wires replaced with Mercedes wires and put in new plug and the problem still exists. This tech says that it is not the fuel distributor.

Odd that from 0-10 mph it is crummy, after that it is fine.

A new coil fixed my stumble on acceleration. m

Thanks. About how much did that cost you? dumb question, but is the coil part of the rotor?

$125 for the coil. The coil is to the left of the engine, located just behind the PS pump and attached to the chassis. Matt these stumbles can be caused by fuel delivery aswell. In fact, I have a big thread where I asked if it could be my coil, then went down the fuel direction only to comeback and replace the coil. It is a very easy diy so i would definately check it.
m

Thanks. I think they just replaced a fuel filter. Amazing. This stumble has been diagnosed for over a week to no avail.

After putting on Mercedes wires, they are saying the car is running worse now.

Does Steve Brotherton have any advice? It would be appreciated if available.

Believe it or not when they replaced the dirty fuel filter, it ran even worse after that. It is running pretty poor after a load and they cannot figure it out.

They are going to slap on a coil on it on Monday and see if that does anything.

They said the only thing it could be after that if the fuel pumps or the air flow meter.

the fuel pumps can be checked by checking fuel pressure. Check before the regulator and after the regulator. Check the duty cycle and eha numbers to see if it really is the AFM. That only needs the potentiometer as the mechanical part very seldom breaks. These guys look like replacers not diagnosticators. I would be wary of just replacing everything as this can get very expensive they can test all this stuff. Most of it is quiet easy now that steve has taught me how.
Good luck.
m

Thanks Martin, I really appreciate your help.

They said that they checked almost everything that it could cause this. They replaced the wires, plugs, (the rotor is new). They said that they checked the fuel pump pressure and it was borderline OK, but was unsure if the fuel "volume" was acceptable - they were to recheck today. Thay also checked the head pressure of the cylinders and replaced the spark plugs after they said one was bad. They thought that there was a misfire at number 2 before they replaced all the plugs because when they witheld fuel from the fuel injectors from #2, nothing happened.

They checked the fuel disitrbutor and do not think it is that. Also checked the EHA.

They said that the only thing that it could be is the coil or the Air Flow Meter, but are thinking that these symptoms that it is not the AFM, but the coil. They will be on a new coil this Monday and see what happens.

They are saying that will a car with 235K miles, it is hard to diagnose a problem like this. Otherwise the car runs great.

Now they are saying that it runs a little better than before on idle, but worse when accelerating. Only if you ease on the pedal is it OK. :mad:

By the way Martin, I read your earlier post and link on when Steve helped you out with the coil situation more thoroughly. I am hoping my problem is the coil as well. One thing that is interesting is that the car does not stumble at idle or acceleration after sitting over the weekend for the first 5 miles (when car is really cold). The tech said that the coil could worsen when the the car heats up and could explain the stumble after that. In any event, the car's temp is affecting something, whether fuel or electrically related.

they can test the temp for the ciruit very easily. plus a new one is only 17 bucks. But that should always be the case from cold, not just after sitting.
m

Thanks.

Update:

They checked the duty cycle (lambda) and is good. Checked the EHA and is good.

Checked the fuel pump pressures before and after regulator and is good (but he says the fuel volume is still not to his standard.)???

He is first going to put another fuel pump to see if it makes a difference and then a new coil. Will put back old one if does not make a difference.

They scope is down so cannot test coil. But reason why replacing is because nothing is jumping out that it is bad or not but sometime is problem (like martin's coil).

Matt, I would go with the coil sure does sound familiar.
m

Thanks. Will know more Monday.

Can you swap coils with a good known one for testing?

Yes, will swap on Monday first thing.

They put on two new fuel pumps - got a tiny bit better. They put on a new coil and it got worse so they are putting the old coil back on.

They said that it now idles fine, but when one accelerates it could be fine or it stumbles like there is a "dead spot". They said that the only thing left that it could be is the air flow meter, which is $1,000.

I am going to hopefully check on it tonight myself.

one thing they also said was that if one accelerates the car slowly, there is no problem, only when one accelerates strongly does it stumble.

Does this sound like the air flow meter or the fuel distributor like the previous tech thought it was?

a new coil should not make it worse. Also the airflow meter is $40-80 cause all you really need is the potentiometer from bosch. I would do a search on the potentiometer cause some one found it for less than I paid for mine. The actual flow mechanism is pretty darn reliable so I doubt very much it is that, rather just the potentiometer. This stumble used to be really common on the old 450 engines and they would also stumble around 55-60 to. God I miss that engine it was so simple.

Thanks. So the $1,000 air flow meter never goes bad? Isn't the AFM different from the potentiometer?

Apparently the new coil lessened the performance for they are putting back the old one. Maybe the new coil is bringing on whatever the problem is even worse. Amazing how much time and money I am spending on this little stumble.

by the way, what does the symptoms from the last couple threads indicate? Essentially, idle OK, but poor performance when accelerate hard.

Before the idles was crummy and accelerated was consistent - poor for the frist 10 mph.

"So the $1,000 air flow meter never goes bad? Isn't the AFM different from the potentiometer?"

Actually, the potentiometer is the one that goes bad in the AFM.
(the pot is part of the AFM)
In the past you had to buy the whole thing (1k bucks), now you can purchase the pot separately (for 40 bucks plus shipping), and attach it to your AFM assembly.