Diagnosing Idle Control Valve
 

86 560sl

High idle. Put 12v directly to the valve for a couple of secs and got a nice click from the valve. I then tested the normal voltage with the engine running. Got 4.0v.

If the valve clicked with 12v, is it good?
Is 4.0 a proper reading while running? Meaning the electronics are good? or?

Idles about 12k in Neutral, about 10 in Drive.

thanks.

JB

I can't help with the voltage question, but idling at 12k does sound a bit high :)

OK, not quite that high...
 

1200 not 12,000. Anybody?

JB

4V is a good reading. The spec at idle is 5V +/- 1V, but at 1200 rpm, it should be higher because the relay should be trying to increase the voltage to bring the idle down.

4V should control the idle. I would look for air or vacuum leaks.

No air, no vacuum leaks...
 

that I can find. Did the ol' spray WD40 around the motor and nothing changed the idle. Only thing that works is slightly pressing on the air intake.

I may try to adjust it but my gut tells me that it isn't the problem.

Thanks.

Jb

What do you mean "pressing on the air intake"? Do you mean the airflow sensor plate?

There is a bunch of other stuff to check. Send me an email and I'll send you the chapter off the CD.

Yes-the sensor plate.
 

Depressing it slightly brings the idle down. I have a copy of the CD but I may be looking in the wrong place. If you have a specific chapter or section I'd appreciate seeing it.

Thanks.

Jboggs

I'm having similar issues, and thought that maybe I also have a problem with the idle control valve. Where is it located, or what section of the CDRom should I look at?

Still working on mine....
 

but the idle control valve is the tube looking thing right in front of the air intake just to the left of the distributor. I've just about decided that mine is bad. If you have multimeter, check and see what voltage you are getting with the motor running? Mine gets 4.0-4.2 and apparently the valve is warn to the point that 4v isn't enough to move it all the way.

Keep in touch.

JBoggs

okay, I think I found mine. Is it about 3 and half inches long, and a little more than an inch in diameter?

This is going to sound really dumb:
I do have a voltmeter, but I am very unskilled with it. How do I use it to check the voltage with the engine running?

No, no, not dumb...
 

I'm no wiz with on it either.
I'll walk you through it. First of all, be careful-you are standing next to the fan and it can take a finger off pretty easy, work from one side or the other. Put th ebrake on also.

Slightly loosen the wiring connection to the valve. Insert the probes from your meter so that one touches one pin one the other. Alligator clips work the best. Set you meter to DC scale 200 I think. Start the car. If your meter reads negative, reverse the leads. Should should get a reading around 4 volts. That's what mine reads. If it's not reading anything, make sure the leads are touchingn the valve but not each other.

Report back your results.

JBoggs

I tried getting the voltage across it, but I can't get it to read anything but zero. The entire time I tried, the car was idling too high. Maybe something is shorting out?


I did pull out the idle control valve and tested it across a battery. The little sliding door opens and closes perfectly with a resounding click.

Did you completely disconnect the wiring harness?
 

The trick is keep the wiring harness connected to the valve while touching the posts with your meter. If you disconnected the harness all the way, the idle would indeed go way up.

If you put the battery to the valve and it clicked, that isa good sign. Mine does that too but the idle is still to high. I'm still trying to solve the mystery as to whether the relay is bad or the valve is bad or something else.

You should also check for vacuum leaks around the engine. Check all your vacuum hoses for tight connections, if nothing is obvious, spray a little WD40 around the top and see if it changes the idle at all. If it does, try to isolate where and fix that.

JB