Strange idle problem, also Hello :)

[MikeCoupe]

Hi, Im Mike. Im new here. I have a '94 E200 coupe (w124 i think maybe perhaps). Ive not had it long but its idling strangely.

Basicly, every now and then when in drive, it throttles up a bit. So it idles at around 1200 rpm instead of about 750 rpm. Doesnt sound like much, but it means that it tries to pull forward more, making it difficult to brake (especially on gravel. The front wheels lock up but the rear wheels still try to drive for a short while.). If I shift into park the revs jump up to like 3000-4000 rpm and slowly decrease.

I dont know whats causing it, perhaps faulty ecu or transmission. Anyone else had a problem like this? Should I sell it before it starts to cost me a lot of money?

(its done 74,000 miles)


Any help would be appreciated. Cheers, Mike

 

[kid-jensen]

Mike,

sounds like a sticky idle speed controller (assuming you have one.......I didn't realise MB made a 200 Coupe).

They can normally be cleaned with good results using an aggressive cleaner like Comma Carb Cleaner. You may get away with a good squirt whilst still on the car, but you're more likely to fix it long-term if you take it off for a proper clean.

Re-lubricate any moving parts because the cleaner will have blasted the lubricant away....

If this doesn't fix it, you're into spending more substantial amounts of money....

 

[MikeCoupe]

I meant 220 coupe lol. It does it occasionally, just seems to be becoming more frequent

 

[television]

It will be the switch contacts inside the air flow sensor

 

[MikeCoupe]

It will be the switch contacts inside the air flow sensor

cheers. Easily fixable?

 

[television]

cheers. Easily fixable?

These contact are the ones that switch over to the idle circuit, what hapens is thet they wear so that they no longer close.

By taking off the top of the sensor plate top, the contacts are on the inside, they wear so that they cannot close, and the cure is to file away the stop part so that they can close.

This can be proved by take off the plug on the sensor and start the engine where it will run at 1200 rpm, take a peice of wire and short the two conacts in the plug together and the reve should drop to the idle speed

 

[MikeCoupe]

I see. How come it does happen constantly? Or will that follow if its left un...filed?

 

[television]

I see. How come it does happen constantly? Or will that follow if its left un...filed?

well to double check before yu do anything, short out the wires in the socket that plugs into the airflow sensor, its the only one there

 

[MikeCoupe]

Anyone able to tell me where the airflow sensor would be and/or look like?

Might give it go today while Im free

 

[aybracers]

Surge on Tick over

If you only experience the problem when you brake to a halt and the car is in gear(Or drive) it may be the same as the problem I had with my 1993 220e. It was the EGR valve.It's on the right hand side of the engine behind the ABS controller. It has two vacuum connections and a push on electrical connection on top and there is a left pointing arrow with the letters MOT(For motor/engine) in front of the electrcal connection. It has a rubber casing that locates on a metal flange attached to the bodywork.If you remove it and check the movement of the valve through the holes in the bottom you may find that the valve pushes down but does not return. They cost about £70 from MB BUT.. you can prise off the bottom cover and carefully remove the diapragm valve,cap and spring. A squirt of WD40 and a quick clean and re assemble and now you should find that the valve works both ways and that upon re installation you hunting/serging at idle has gone away.

I found most of the answer here and on other forums but it had baffled my local MB specialist who was starting to talk about Air Mass sensor replacement.