92 300E idle problem
 

Hi,
I just bought a 92 300E last week. I got a good price on it because the ABS light was on and it had no A/C. Turns out that the A/C had a unplugged wire and when I plugged it, it started to work just fine but my engine wouldn't accelerate when the compressor went on. Last Saturday I was taking a cruise on my car when I decided to hit the overdrive and see the responce on my car. As the car accelerated into overdrive it suddently stalled. I had to get it towed back to my house. I thought that it might be the fuel pump or the fuel pump relay. So someone posted something about the the fuel pump relay getting a loose solder point or something so I removerd the relay and there was nothing wrong with it. I did however clean the contact points because they were a little dirty. To make the story a short, the problem was the rotor and the distributor cap. I replaced them and the car started up fast and the ABS light went off. When I turned the A/C on the cars idle rose tocompensate for the lose, "something it wasnt doing before", but it's out of control, when the car is cold the idle works fine but when the car is hot the idle goes out of control and it turn off on red lights or on stop signs. Anyone have any ideas....."I ran out of ideas"....lol

I have looked deeper into this and I found out that it works fine on cold but when the engine gets to the the normal hot temperature, the idle control valve stops working. then I turn the engine off and re-start and it starts to work again for 15 or 20 more minutes.....any ideas? I think that the power to the control valve stop getting to it....it's not really the control valve...

Possibility the over Voltage Protection relay is faulty....it lives behind the rain cover back of the battery...has a red 10 amp fuse on the top.
Check the date on it...older than 5 years it's due replacement.

The frequency control setting is very critical for warm idle control.
Target speed is 800 rpm +/- 50 rpm.
If the c/o value is off, this will overdrive the fuel mixture control and cause the idle to fluctuate or stall.

You need to check c/o frequency...should be 50% and fluctuating a little...............
the coolant temperature sensor also sends a signal to the ECM to tell it what the operating
temperature of the engine is to adjust fuel and timing.

Cold....pin to ground....2000ohms or more.
Warm...380 to 360 ohms.....both pins should read the same....it's a two pin sensor at the rear of the cylinder head next to the number 6 intake runner.


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ok, I'll look into that tomorrow because when I bought the car the idle control valve was not working but it really didnt stall untill I turned the A/C on. It would cold start good and run good when hot. But just last sunday I was looking behind the battery and noticed that the relay you mention had no fuse and I placed a 10 amp fuse in it. I really didnt know what that relay was for but I noticed that when I started the car that the idle did change. When I turned my A/C on the engine did jump 800rpm's....or so. So tomorrow I will remove the relay and clean the pins good and also remove the idle control valve and clean it to make sure its not sticking or something......

The original OVP's are a known bad part.

Use the search function to find the part #.

If yours is the old, bad part #, then change the part. Cleaning it will do nothing.

Pull the OVP and shake it. If you hear rattling, it's a goner.

Be sure to hold the flap down while you're shaking the OVP. This is not a conclusive OVP test, but a lot of the older ones will rattle when shaken, indicating something is loose inside.

yeah guys, I took the realy out today and lloks to be ok. I did also take out the idle control valve and clean it with carburator cleaner and oiled it with wd40. I also replaced the peace of hose that goes from the carb to the valve, I was going to replace th other one that goes to the injector......but it was too complicated. After putting everything back together I started the car and noticed that the valve was responding faster and with more precision. So far so good. I'll post some more when I take the car for a spin tonight.

The OVP's always look good. A visual inspection is worthless.

If you have an original OVP with the original part number, replace it. They are cheap, anyway.

You can't tell by looks. ABS light on is a good indicator the OVP relay has problems. Cracks in pin solder joints inside the case is the usual failure, and they can be reflowed if you are handy with soldering equipment, once you take the case off. Else, buy a new one. Pulling and re-inserting the OVP might get you going briefly, but it won't last.

Steve

Damn, the ABS was on, because when I bought the car there was no fuse in the relay and the ABS light was on. After I installed the fuse the ABS light went off and the control valve started to work. I'll just replace the relay and avoid further trouble!!