Idle control valve - PeachParts Mercedes-Benz Forum

mhingram · #1 12-12-2002, 02:06 PM

Does anyone have an idle control valve that they know is good that I can test with. I will pay shipping and handle each way. Just want to test if my wierd idle is that or a bad injector. I have a 91 560sel
Thanks
m

ILUVMILS · #2 12-12-2002, 07:41 PM

What's weird about your idle?

mhingram · #3 12-12-2002, 08:01 PM

Lumpy, worse in p then in d which makes sense, as the least amount of fuel enters the system in Park. Not electrical as far as I can tell scope looks excellent, plus I have new plugs, cap, rotor and wires. I am down to my idle control valve or a bad injector I think. I wanted to test the idle control valve before I blue print the injectors to determine the bad one or ones.
m

mhingram · #4 12-13-2002, 09:45 AM

anyone out there with a loaner please?

sbourg · #5 12-13-2002, 10:03 AM

If it is a rotary idle control valve, it is easy to check for smooth operation. The angle of the shaft and thus the size of the port opening should vary smoothly and consistently as you vary the current to the terminals. Any stickiness in action, and you should clean it in solvent, using wood-stemmed cotton swabs to work off any tougher deposits. I used rubbing alcohol.

Not much else can go wrong with it, but lots of opportunities for air-path leaks elsewhere in the rubber plumbing.

Steve

mhingram · #6 12-13-2002, 12:37 PM

I will try that thanks
m

mhingram · #7 12-13-2002, 01:58 PM

I have replaced all the rubber by the way and it is not a bad idle just enough to be annoying. I can hardly notice iy anything but P. I think is a bad injector but wanted to make sure with a tester.
I will let you know if cleaning helps.
m

ILUVMILS · #8 12-13-2002, 08:37 PM

I'm not exactly sure what you mean by "lumpy". If the idle is slightly rough, then I think checking the injectors should be considered. Most idle air valve problems will result in an incorrect/fluctuating idle speed. Check the "Llambda" before you go any further. This is a good way to determine if you have a rich or lean condition. I've seen a few 116/117 engines that develop vacuum leaks at the rubber boots that seal the upper and lower sections of the intake manifold. Keep in mind that there are many vacuum leaks possible, so check the easy stuff first. As you said , the ignition system is good to go, so look carefully for vacuum leaks. Other things worth checking if all else fails: 1. Carbon build-up on intake valves(you can check for this if you remove the injectors). 2. Cylinder compression(It's free if you do it yourself, and it's conclusive). 3. Timing chain stretch. Good luck

mhingram · #9 12-14-2002, 01:57 PM

check the lamda and it is on the money, did check for vacuum leaks have not found one yet. Did the direct injector blowout with 3 cans of cleaner and the engine is clean as a whistle. So I hope it is the injectors been avoiding that as much as possible but looks like it is all I have left.
m

steveholz · #10 12-22-2002, 01:45 PM

Did you solve your problem? I had the same problem before my idle went high. It would come and go and fuel injector cleaner and running on the road seemed to help.

mhingram · #11 12-22-2002, 11:52 PM

not yet, it really is not to bad in D, I am still not sure if it is the injectors or the idle valve. I am going to soak the idle valve next week and see if that helps.
m

pmizell · #12 12-23-2002, 12:39 AM

How did you go about checking for leaks? Visually or with starter spray?

If former, buy some starter spray and spray all around the hoses and listen for increase idle. Some cracks are so small in those rubber hoses that you can't see them.

I had an idle surge problem that was cured by cleaning the idle valve with laquer thinner (fill it up and shake it well) and then lubricated with WD-40.

G'luck :p

ILUVMILS · #13 12-24-2002, 04:42 PM

A word to the wise about looking for vacuum leaks by spraying anything at potential problem areas. The propellant in the spray can will find it's way into the air intake and cause a momentary change in idle speed/quality! Don't ask me how I know this!!! You can waste a lot of time chasing ghosts unless you eliminate this possibility. I've used a rolled up piece of cardboard to act as a snorkel over the air intake. Depending on what engine you're dealing with this takes a bit of imagination, but it's worth the effort.

mhingram · #14 12-29-2002, 02:08 AM

Okay cleaned the idle valve this weekend after I did the oil and transmission fluid and filters. My Idle in Drive or reverse is marginally better. However, my idle in park is worse. First, the idle rpms picked up to about 850 rpms and it fluctuates around 750 to 950, very strange. I am begining to believe my idle problem is the idle valve. Anyone think I am barking up the wrong tree.

ILUVMILS · #15 12-29-2002, 07:05 PM

Check the throttle valve switch. The connector is on the intake manifold at the front, slightly to the left, and has three pins. This switch tells the control unit when the throttle plate is at idle, or at full load. I don't remember the color of the wires, but it's easy to test with an ohmmeter. A quick way to check this is to determine which pins are for the idle signal. Just bridge the appropriate wires and see if it makes a difference in idle speed/quality. What you're essentially doing is fooling the control unit. Make sure you determine the correct wires before you do this. The great thing about this test is that it's quick, free, and CONCLUSIVE.