High idle at times

[Kevin Gallagher]

I have a 84 380 Sl with a race condition. This fast idle comes and goes. It is 1700rpm then drops to 1100 or the normal 800. Cold or hot winter or summer. Following the form I found the relay area and cannot tell which is which. One says a black large one, another says it's the only one with a 10 A plug in fuse on top. I am confused. I am looking right over the fuse block on the side under the glove compartment

[rememberjeff]

Cant help you with the mechanics, but I had the same problem.
When my mechanic replaced it, the problem was fixed.

[RickM]

This is a very common problem with a few causes.
First, the idle control unit is behind the glove box. Remove the few screws and light connection and remove the box interior/liner. When looking into the cavity, straight ahead, you'll see a few white plastic (Vacuum actuators) canisters and to the left of them a component that resemble a large relay (see below). I believe one screw needs to be removed to unplug and release.

Be careful when buying a used unit. I bought a used one on EBAY and it made the idle condition worse. Convinient that the guy insisted on no returns. Make sure you get a money back guarantee.

Another approach is to disassemble the unit and go over the solder joints. This has worked for many. A search will describe other possible causes and testing procedures.

[Kevin Gallagher]

Thanks Rick. I was looking in the wrong place. I do have a large relay box like that under the foot rest part of the floor. A hinged door comes off and there it is. I will however look where you said. Also do you or anyone know where the idle control is under the hood. I should check that also.

[RickM]

Kevin,

When you remove the air filter housing you'll see the Idle Control Valve hooked up to two rubber hoses and a electrical connector.

I removed mine and used a 12v power supply to confirm proper movement of the piston under power. You must also verify power getting to the unit at the proper time as well by using a Voltmeter at the connector when installed.

While I had it out I cleaned with Brake-Kleen and re lubricated the piston mechanism. It's very easy to do.

[Kevin Gallagher]

Thanks again Rick. I just removed the relay thanks to your picture and what to expect. It is a sealed box but I guess I can get it opened. After that I will follow up on the valve. It will take a day or twoince I spend little time each day on it. I'll keep you posted.

[RickM]

Kevin, Glad to help.

To remove the cover lift the catches on the sides of the relay and put a toothpick under it to keep it opened. When you get most of the way around it'll come right off.

Good luck.

[Kevin Gallagher]

Rick,
I sent you an e-mail by mistake. What I was asking was how to get the valve out of the rubbers. You can read the e-mail for the relay box status.

Thanks,
Kevin

[RickM]

Kevin

I can't remember if there are clamps or not but essentially the tube comes off very easily.

[Kevin Gallagher]

After all is said and done I did remove the idle relay and cleaned it and its contacts. The condition improved to where I can live with it. It is happening anly at times and doesn't last but a couple of seconds. So I know it's the relay. I'm leaving it as is since I have decided to sell the car. It is in tip top shape with all original parts and only 43,00 miles. The only thing it needs is a muffler system. I'm going to look for about $19,000 but don't know how to go about selling it. E-bay? or what

Kevin