I have a problem with my idle. Some background: I was having surging and hesitation, so I had my mechanic put a new throttle actuator in. It ran great for a few days, cruise control worked again, then it started to have problems again. The problem is different this time. The idle is too high. In Park or Neutral, the car will rev between 1300-1800 RPMs. In Gear, the car will rev between 900-1200 RPMs. The high idle causes the car to practically drive itself; in stop and go traffic, I constantly must ride the brake or the car will accelerate up to 30mph or so on its own. Also when this occured, the cruise control would not work at all. It started as an intermittant problem, but now it seems to be occuring all the time.

All signs pointed to a faulty throttle actuator. I had my mechanic replace the throttle acutator with a new one. Same thing happened. His handheld scanner idicated that the throttle valve (or something like that) was open when idling, when it should be closed. Any ideas would be greatly appreciated. We're having problems figuring out what is going on. I'm thinking something is faulty with wiring or even the computer unit itself.

On a side note, I failed my emissions, and nothing obvious is wrong with the engine. Mechanic is leaning towards replacing the cat. I had the cat replaced a year and a half ago just before I bought the car, but it is a non original part. My mechanic says it is a piece of junk (the cat). Could the throttle problem be linked with emissions? I hate to put a new cat on if it won't solve the problem.

Thanks,

Matt
94 E320 158k

Is the engine wiring harness original?

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95 E320 Cabriolet, 159K

Wiring harness replaced in April 2002.

Air mass meter tested ok.

Maybe a vacuum leak?

Or does it sound electronic.

Have you checked the throttle cable itself? It may sound dumb, but my idle was going crazy, high, low, fluctuating, etc. I did two things: made sure the cable was all the way out, with a little slack, and then tightentned a clear vacumn hose on the intake manifold next to the throttle cable. It now idles perfectly. If the cable has no slack, it is like constantly being on the gas. The computer begins to "hunt" for the correct air / fuel mix, and the idle is not correct. Check this first. Is your "check engine" light on? If not, I can't see why it failed emissions test. If your oxygen sensors have not been replaced in 30-60k+ miles, then they could be the problem, and will cause the emissions failure, and maybe the idle? To clear the computer, disconnect the batt for a couple of hours and try again.

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro

Thanks for the post. I think the throttle cable is ok. It was the first thing my mechanic looked at. No check engine light. Mechanic put in new oxygen sensor, due to it being "lazy", but it still failed miserably. HC and NOX were both really high.

I gotta check that intake manifold to make sure it's not leaking.

I wouldn't say the engine/computer is hunting for the right idle. It seems to just jump up and stay up at this high level. Once it starts idling too high, the only way to make it go back down to normal is to restart the engine, and then it only works maybe 1 out of 5 times. Then after driving for a while, it can jump back up. It's unpredictable when the idle speed will increase, however, once it is too high, it stays too high. You can't notice any change while at cruising speed. It's only at slow or no speed that you can tell.

Maybe it's the return spring wrongly attached, or the throttle valve idle speed contact (S29/2) is not operating.

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Steve

1992 300CE Sportline Sophie
1990 300E Emma - in the family
1979 240D Josephine - sold, but not forgotten
2004 Pacifica AWD

http://web.mac.com/dakota/Mercedes/Home.html

Any other possiblilites? As I'm going to call my mechanic today with some suggestions (the car is at his shop).

Did you check the idle speed control module?

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94 E320 Silver 210000 miles
94 740il Pewter Green 97000 miles- Retired
05 S430 4Matic
07 Lexus IS250

M104 engines do not have an idle speed control module.

It is part of the throttle actuator, which is also called the ISC / EA / CC module:

Idle speed control
Electronic accelerator
Cruise Control

If your throttle linkage is not screwed up, and if your idle isn't hunting around, then I'd have to assume something is wrong with your actuator.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Where is the Idle Speed control module located?

But 2 actuators with the same problem? What are the chances of that? I'll have to have my mechanic check the linkage and for vacuum leaks.

When a new throttle actuator is put in, are there any special procedures that need to be followed for the computer to relearn the throttle position? I found some info on this in the archives, but don't know if it applies to my model, or if it could cause problems like this.


Thanks,

Matt

Do codes 6 and 17 give any clues? Anyone had these codes before, and if so, what to do to fix them?

Thanks,

Matt

I also read the posts about re-learning the throttle stops. When I replaced my TA, I turned the key to the on position and waited. I could hear the throttle plate moving from open to closed. You can hear the buzzing motor and a click when it changes directions.

I don't know what sends it into re-learning mode though. You might disconnect the battery, unplug the TA to simulate changing it, put everything back, then turn the key to "on" and listen for the learning mode.

Just an idea - otherwise, you might call someone who really knows this system and ask about getting it into learning mode.

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

Finally seemed to fix the problem with my high idle. My mechanic replaced an electronic module under the front passenger floor... it has the words VDO on it (not sure of the part # as it's not in front of me). Not cheap, but fixed.

My emission problem was fixed with a new catalytic converter. Also not cheap, but fixed.

Just hope this can answer any future questions that may come up.


Matt
E320
167k