How do you know if the throttle actuator is bad? I usually have a very hard time starting my car (when cold) and once it's started, the idle is way too low....around 450-500, and sometimes 350 or so. My cruise control doesn't work most of the time either.

Of course, there's once or twice a week when I start the car, and it idles perfectly around 1000 when cold and slowly decreases as the car heats up. The cruise works perfectly in these conditions.

I'm wondering if it's the throttle actuator, or (hopefully) something else that could be causing these symptoms. How do I rule out a bad throttle actuator? And isn't it kind of strange that everything can run perfectly one day, and terribly the next? Maybe a lose wire or something?

Thanks for the input.
Matt
1994 E320
150k

Have you checked the wiring harness? Some of the 94 E320s had the insulation on the wires turn to powder.

Pop the crossover pipe and see if the actuator is gummy and carboned up. If so, clean it.




Joe

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The first thing that you should do is have someone with scan tool for MB check the EA(electronic accelerator) computer for codes.

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I had the wiring harness replaced about a year ago, after it failed. I don't know if there is a different wiring harness that I need to replace, or if the old one caused a short out somewhere in the throttle actuator itself, which ruined it. That's my biggest fear. I've only owned the car for a year and it has never idled well...just now it has been worse.

Thanks.
Matt

This car has an EA computer? It doesn't have traction control, and I thought it was only those cars with the drive by wire system that had an EA computer. WHere is the EA computer in the engine bay, and where is the actual throttle actuator itself??

I guess I'll have to go to the dealership or my mechanic and have those codes scanned.

I appreciate all the responses.

Matt

The EA/CC/ISC computer is inside the car under the passenger carpet. ON your application it controls cruise control & idle speed adjustments. IF your car has ASR then it also controls that feature as well.

The throttle actuator is mounted directly to the "lower" section of the intake manifold.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Last night I had a weird incident maybe related to this idle problem of mine. I was driving on the freeway at 70-75 mph and while I was exiting off the car had no response from the accelerator. It just coasted, but the car stayed on. A total helpless situation. I went through a green light (thank goodness it was green), and pulled onto the shoulder. When I tried to accelerate, the car's idle oscillated quickly (2-3 times/second) between 1000 and 1500 RPMs. Even when I floored it, this oscillation happened. I turned off the car, turned it back on and drove another 15 miles home with no problems. I drove to work this morning and had no problem. It reminded me of when my wiring harness failed on the freeway and the car stalled (no response from the accelerator.) Anyone have any ideas??

Damn electrical gremlins again!!

Thanks,

Matt
94 E320
151k

My car has exhibited the weird idle oscillation (between 1000-1500 RPMs) several times in the past month. The common link between all of the incidents is that it happens the day after it has rained. It has only happened about once a week, and right after I start the car in the morning. The RPMs will go up to about 1400-1500, then the engine seems to shut all fuel flow off, until the RPMs drop down to 1000-1100. Then the engine jumps to life until ~1500 RPMs, dies, then kicks back in at ~1000. I noticed that when it happens, a hissing sound (like a blowoff valve or something) is coming from the back of the engine (towards the passenger compartment). The whole process repeats continously until I restart the car. Once I turn off and restart the car, the car runs normally.

I have a couple other issues that have to do with a surging idle. They are: low idle, surging idle while switching from P to R/D and when the engine is under load (a/c on), hesitation, rough idle, and a mostly non-operational cruise control.

I've read some of the older posts on this topic, and am worried that this could easily lead to a mechanic just recommending change the MAF sensor and/or the Throttle acutator without checking other, simpler things first. I wonder if the hissing noise from the rear of the engine could indicate a vacuum leak, or something else related. I just had the 150k service 2k miles ago, with new spark plugs and fluids. I was also having a hard start problem about a month ago, but that has sinced worked its way out on its own. Oh, and the wiring harness was replaced a year ago.


I appreciate any advice, as I plan to go to the mechanic in the next week or so.

Thanks,
Matt
1994 E320
152k

ovp?

replaced that with the wiring harness about a year ago.