epowers777

Ok been on another forum and sent me here. My 86 Mercedes 300e inline 6 with 80,000 miles is having an idle problem. I bought the car and it ran good then idle went to poop. The mechanic (previous owners) pinched the temp sensor ( green 3 prong) in between the air filter housing and the wire grounded out. SO I fixed the wire changed the temp sensor, Cold start valve, idle valve, checked the red top fuze relay (opened and check solder seemed good) and checked fusses. Also my aux fan wont kick on. The car starts and idles at around 800 flat (doesn't rise when cold) and goes to about 550 when put in drive. (pretty ruff in drive). The car drives great really smooth when on freeway. So I think its electrical so please tell me what controls the idle? relay fuse? Also whats suppose to happen when you unplug your temp sensor? I know that controls idle and when I unplug mine it does nothing just keeps idling crappy!!!

PLEASE HELP!!!!!!!
Compared to my buddies 92 mine should rise idle at cold start and compared to his mine idles ruff!!

epowers777

http://www.mercedesforum.com/m_99017/tm.htm
My old posting if you want to read.

YNVDIZW124

The fuse on the OVP may be ok but i would replace it. That temp sensor is only for the aux fan and the temp gauge. The CIS-E temp sensor is actualy black 2 post towards the back of the engine by the 6th cyl injector. You might want to also check your idle control valve. Take it off and clean it off with some brake cleaner. Also, if you can replace your O2 sensor.

epowers777

The 02 sensor is brand new. I already cleaned out the idle valve. The last sensor near the 6 injector is a injector sensor I thought. Is it? the second one is for the guage and third one (green top 3 prong) is the temp sending unit.

YNVDIZW124

That black temp sensor tells the EHA valve to enrichen the mixture for 3-5 sec when you start the car. How does it idle when running after warming up?

epowers777

the black temp sensor?? the one by six or the gauge sensor. It runs the same when its warm no difference.

YNVDIZW124

So far what have you done to the car and what is the history or parts that you've replaced? ...It's the one by the 6th cyl injector.

epowers777

i bought it from a guy he said it sat around for a long time because it never ran right from factory ( thats what main owners said) so He took it to Mercedes and they kept it for a month flew some dude out to look at it and found out it had wrong computer in it so they put a new on. They put new computer, radiator, cap, AC Compressor.
I put on new o2 sensor, green 3 prong temp sending unit, idle valve, spark plugs, cold start valve, new fuze for aux fan. oil change.

epowers777

checked out the sensor on cylinder 6 is green top to with female fittings and the wires are male . One had white residue on it when I pulled the plug so cleaned it with wd40 plugged back in started ran same unplugged sensor and it dropped idle to 500 ran way ruff plugged back in and ran like usual.

SO when you start your car cold what are the rpms? What does the thermal vac valve do?

YNVDIZW124

When you start the car when cold it should be at around 800-900 then it slowly goes down to 500-550. I would change the distributor rotor and clean the cap with a flat screw driver. Buying a multimeter is a must for these cars to check if the electronic components are working properly.

shdoug

It sounds like there's no power to the idle control valve. The Red/Yellow wire from OVP terminal #87 supplies power to the idle control valve. Check OVP fuses, or OVP itself.

epowers777

Well kind of good news. I started and it started idle at 550 then it rose to 900 for about 50 seconds then dropped back down 800 and got ruff again. I spraid the end of the wires with wd40 then plugged them back in. The rotor sometimes makes a noise but looks brand new. The thing that spins doesn't look that good. How do I test the wires? Can you test the cap?
There are juice going to the idle valve I plugged in my spare and it moves while the car is running. thats what I wanna do this is about what im ready to do!!!

epowers777

Anyone?

shdoug

If the cap looks like it was in a fire it is probably bad. Otherwise it's probably OK. The cap and rotor go bad over a very long time, usually. If your problem started immediately then I would look at something else.

tokleman yanass

I just replaced my distributor (86 300e 88K miles) - might be about that time. mine put me on the side of the road though. The two pin coolant temp sensor at the rear of the engine sends a resistance signal to the ecu which drops over about 10 minutes as the engine heats up - if its faulty then the car will start and run for about 10 minutes then start missing and cutting out. the other temp sensor sends a signal to the temp gauge in the dash and controls the aux fan.

tunayballa

I'm having an identical problem in my 190e. How does yours idle? I know rough, but does it surge up and down? How does the car go from a stop light when you step on the gas? Does it kinda shake before finally taking off or some sort of hesitation? Also, how does your car start? One start or you have to crank it for a couple seconds?

epowers777

My 3 prong geen top sensor was bad. When that was bad once it was warm I would stop at stop light and when I took off the car would spudder. After that fix it was my wires and the red top relay were bad thats why my idle was bad

Patz

This happens on my 95' E320 (95k miles) every once in awhile. Also, when I'm stopped at a light and I have the A/C or heat on, the car starts to shake the idling gets so rough. Is the shaking the kind of "rough idle" that you all speak of? I know this has been a typical problem with the W124 as I see people posting about this all the time.

I am mechanically challenged so I probably wouldn't be able to do the above fixes. Anyone know how much those might cost at a shop? Trying to sell my car, and don't want to give the buyer a false estimate on necessary repairs.

Thanks - off to search for more "rough idle" threads.