Sounds like a high RPM flu going around. Just yesterday my 1991 300CE started a high 1700 idle after a short road trip of 100 miles. I did use cruise control which I don't often use. It worked fine. After a few starts and stops, the RPM drifted down to a steady 1200 at idle and by evening it settled in at 1000 RPM idle and about 800 RPM in gear with foot on brake. Prior to this the engine had a normal idle of about 750 in neutral and 650 in gear. There is no ABS light condition. The 10 AMP fuse on the OVP is fine. I have a new OVP that has two fuses on the top instead of one. I changed the ICV with a used unit about 2 years ago. With my model car is there an idle control unit that needs to be checked? I guess the first thing to try is the new OVP. I stil have the old ICV that I think is still good.

Anything else to check?

Thanks,

glenmore
1991 300CE
2000 C280

As suggested a resolder of the OVP will normally work . Mine had a cold solder joint near the zener tip.
mak

Well, swapped in a new OVP and no change to the idle situation. Still stuck around 1000-1200. Next up, swapping out the ICV.

glenmore
1991 300CE
2000 C280

High idle could be caused by a vacuum leak, or a bad connection at the idle control module.

Be a shame to replace a part (again) only to have the same problem.

Might want to check your coolant temp sensor as well.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

I have a used ICV that I believe is good and will swap it in. Labor is free! Is the idle control module a different part and where is it located?

Thanks,

glenmore
1991 300CE
2000 C280

ICM is what controls the idle control valve. On later engines, it's integrated into the ECU, on older engines it's a stand alone unit that apparently can be fixed by a simple re-solder job. Check your firewall. I'm guessing since your's is a '91, it's probably integrated.

What kind of voltage do you get from the wire at the idle control valve connector? If it's 0, it's not the ICV, but it could also just be bad wiring or a faulty/corroded connector.

And labor is not free - even yours.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

As a "test" while my engine was idling high, I took a toothpick and used it to gently push the contacts on the OVP relay together, and the idle went down to normal, no problems! As a further test (ok, I mean jerry-rig) I put a cigarette butt in their to keep the relay contacts closed, and drove the car to work, etc., and it ran like it used to before the problem. All solder joints were re-soldered, I checked the zener diode with a multimeter, it measured ok, but I guess it could be breaking down under an actual load, I even cleaned the female part where it plugs in, checked some ground wires (?) at some block or junction behind the OVP, but the only thing that fixes the high idle is the before mentioned "fix". I'm pretty sure the relay is bad (diode or whatever) The dealer wants $90.00 for a new one, I guess I'll have to get one unless someone knows where to get one cheaper. I have to drive the car to Houston tomorrow (235 mi. from me) I sure hope my jerry rig doesn't screw something up!

I guess it's the OVP, as I have nothing else to check. Also, someone must have had the instrument clester out for somereason,as the ABS light doesnt come on at all just some unmarked light to the immediate left of it. I wonder what that light is for?

Thank you for your help. Swapping out the ICV made no difference. From what I can tell, both ICVs are OK, they have a nice clack clack when voltage is applied. The short hose on the right of the ICV had a crack in it. There is just enough room for a hose clamp but it didn't seem to make much difference. The little hose is $28! With the ignition on, a voltmeter at the ICV plug showed 1.92 volts. With the engine running and the plug pulled out a little, the voltmeter on the two ICV pins showed 6.2 volts.

Thanks,

glenmore
1991 300CE
2000 C280

Replace all the ICV hoses. Even small leaks cause big problems. Sounds like the idle control is working just fine.

As a test, with the engine running, disconnect a vacuum fitting or two (that comes directly off the engine) and watch the ICV voltage. If it doesn't change, it's probably maxed out, indicating a leak somewhere.

Also, check to make sure your cruise control isn't tugging on the throttle. While running at idle, the throttle should be fully closed. If you can close it more with your hand and get a normal idle, then that's a definate clue that something's going on with your cruise control or the linkage to it.

Heck, could be as simple as something stuck behind your gas pedal. Believe it or not, I've seen it more than once.

__________________
A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.

Thanks for all the responses (original poster) I have read all responses and learned a lot, haven't had a chance to try any fixes till today, this is an extra car, cleaned ICV hooked power to it. it opened and closed ordered a ICU-- here Tues checked Relay fuse is good pulled out of car idle dropped from 1700 to 1200 will try to re solder You people are very helpful --really surprised by all the replies Thanks again

No shortage of information here, sometimes, you get a little more than you bargained for, but it all helps in the end. My mercedes, I know inside and out, thanks to the folks here on the forum.

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450

Ditto on the thanks to everybody! I'm still having my high idle issue, but I am learning a lot about this car ('87 560sl), and I can't wait untill I have some kind of knowledge to share, right now, I am still in the learning stage!
My previous 'Benz's have all been diesel, and I never had a problem I couldn't figure out. Not so with gas-powered Benz!

I know what you mean..didn't have Vacuum leaks to contend with when I had my 300SD on the road. The possibility still exists that I may do a swap at some point.

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450

I am waiting for ICV hoses and assorted vacumn parts before moving ahead. On short drives my car will settle in at different RPMs. Sometimes at 1500, sometimes at 1200 and sometimes at 1000. Sometimes it will go back to normal idle of 750 for awhile and it would appear that nothing is wrong. Then with the next drive the high RPM would be back. Does this behavior narrow the focus to any particular part?

Thanks,

glenmore
1991 300CE
2000 C280

That still points towards the ICV and ICU. Even my older ICV would do that before I freed it up a bit, it's the old coolant type. which I may bypass for manual.

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450