Idle Control Module Unplugged; No Change
I apologize for troubling everyone but I've searched the forum and cannot seem to find a discussion I saw a while back on high idle and Idle Control Unit/Module.
Once the car has warmed up it idles at about 1500 to 1800 and I've tried all the initial replacement/repair/clean steps to no avail. Now I'm digging deeper.
I unplugged my ICU but there was no change. I remember seeing a discussion about possible link to temperature sensors but cannot locate that information.
Can someone point me to it?
Sort by Oldest first 1,032 posts · Joined 2011If you are lucky, the Overvoltage Protection Relay, above the fusebox is faulty, if so, the ABS warning lamp should be on. (unless someone removed it). Have had this problem about 3 times in nearly 30 years, all cases was a faulty ICM, replacing the output transistor usually helps.
The temperature sensor, gear position, AC compressor and vacuum sensors would only change the idlespeed by 200 rpm. Attached is the wiring diagram.
Attachments 41.8 KB Views: 4,285 3,162 posts · Joined 2011Sure you have the right idle control module ?
81 is different from all years following.
Ned to recheck the idle air controller as well.
rockyx Discussion starter 54 posts · Joined 2013thanks for the feedback.
I had already replaced the OVP relay with no improveent.
I have a remanufactured ICM in hand ready to install but didn't want to open the package until I could confirm I had addressed everything else. I'll have to better understand the "output transmitter" so more digging.
benzbarz, thanks for the caution on having the correct ICM. I will confirm. You also reference an "idle air controller". Is that the same as the idle control valve on the front of the engine? If so, I've taken it out checked it and cleaned it and replaced it with all new hoses. If not, can you tell me where it is located?
Thanks for the help. Back under the hood/dash today to see what I can do.
3,162 posts · Joined 2011High idle usually represents air leaks, aside from obvious throttle linkage adjustments, first obvious step to check the idle air valve/controller/slide whatnot.
A cheap Swisher Sweet can provide smoke for testing the system as well, just pucker up and blow.
You can do that, can't you Rick ?
2,182 posts · Joined 2009The 1981 380 has an extra relay in the system the later models do not, it is the voltage supply relay. I had posted on this years ago, and all I can say is the relay is not located with the rest of the relays, but appeared to be behind the glove box and above the idle control unit to the right, but never had it confirmed. The last person that had this problem just jumped a wire to provide 12 volts to the ICU.
Check pin socket #2 of the Idle control unit for 12 volts with the ignition in the on position. If not there, jumper 12 volts to it, and try the system and see if it works properly. I will post a diagram of the 81 in a bit but have to change computers to find the file..
If I knew I was going to live this long, I would have taken better care of myself and saved more money
rockyx Discussion starter 54 posts · Joined 2013The 1981 380 has an extra relay in the system the later models do not, it is the voltage supply relay. I had posted on this years ago, and all I can say is the relay is not located with the rest of the relays, but appeared to be behind the glove box and above the idle control unit to the right, but never had it confirmed. The last person that had this problem just jumped a wire to provide 12 volts to the ICU.
Check pin socket [URL=http://www.benzworld.org/forums/usertag.php?do=list&action=hash&hash=2]#2 [/URL] of the Idle control unit for 12 volts with the ignition in the on position. If not there, jumper 12 volts to it, and try the system and see if it works properly. I will post a diagram of the 81 in a bit but have to change computers to find the file..
Rockcrusher, I found the voltage supply relay but have to ask how in the world you get it out. How would I test it in place.
Also, sorry for my brain density, but exactly how do I test pin #2 on the ICM? I put a meter on the pin and then grounded it to the car and got nothing. then I closed the circuit by putting one test wire on pin#2 and the other in the #2 pin socket of the plug that goes to the ICM, still nothing.
I hope that makes sense. So is my conclusion, since I got no power on the #2 pin, that the ICM is bad and should be replaced?
Thanks for your help.
2,182 posts · Joined 2009Here is a diagram for the 1981, and the 1982 and on.
The extra relay is #29 in the 1981 diagram..
Attachments 62.1 KB Views: 4,545 71.1 KB Views: 4,084If I knew I was going to live this long, I would have taken better care of myself and saved more money
2,182 posts · Joined 2009The 1981 380 does not have the over-voltage protection relay with the piggy-back fuse either, it has the fuse built-inside the relay. and that's all I know about that.
If I knew I was going to live this long, I would have taken better care of myself and saved more money
3,162 posts · Joined 2011The OVP on 81 is usually a red ice cube relay, has a small hole on the bottom where a thin internal wire can be seen. supposedly how the fuse is checked.
32,795 posts · Joined 2008My first thought was if you have a high idle and unplug the idle control with no change the ICU is bad.
2,182 posts · Joined 2009Unless it's not getting power to begin with. I believe the idle control valve is powered by the same 12 volt input through the Idle control unit.
If I knew I was going to live this long, I would have taken better care of myself and saved more money
rockyx Discussion starter 54 posts · Joined 2013Thanks for the additional info, diagram, and test procedure. All will be put to use this weekend.
How long does an ICM last? The one on the car right now has "remanufactured" stamped on it so it is clearly not OE? I'm thinking I should just go ahead and install the new one since I have it in hand. Then I'll know it's good and eliminate it as the problem. But first I will test that it's getting proper power.
2,182 posts · Joined 2009Just got back from the fall color ride.
You need to check for 12 volts in the plug that attaches to the Idle control unit, I don't have a pic, it should have numbers by all the sockets the pins of the ICU plug into.. stick the positive probe of the meter in the socket, ground the other lead, turn the ignition to the run position not start position, and check for 12 volts.
Where did you find the power relay. take a pic if possible.
Voltage comes from the battery terminal block to pin 1 of the over voltage relay, then out of pin 6 to pin3 of the power relay, out pin 1 to: pin 8 of the lambda unit and pin 2 of the Idle control unit.
If I knew I was going to live this long, I would have taken better care of myself and saved more money
rockyx Discussion starter 54 posts · Joined 2013Ok. I went back and retested the #2 socket and made sure I had a good ground and this time I clearly got 12v on the meter. So I now know the ICM is getting proper power.
It's idling about 14k to 15k in park.
I'm going to retest it, but I think I have a bad temp sensor on the back of the engine. It was mentioned in this thread that replacing this would likely bring the rpm down about 200. So that would get me down to about 12k to 13k.
I also sprayed some carb cleaner around the engine in several key places to see if I could spot any vacuum leaks and I found a spot on the front of the air flow boot. I put on a new boot several months ago but apparently was not very careful to make sure it had a good seal.
So if the vacuum repair and the water temp sensor replacement together bring the rpm down to 10k to 11k I'm getting closer to spec. If the ICM is bad, which it seems like it may be, then I believe I should be able to bring the high idle down to a proper level.
Now I'll need to deal with hesitation and stalling at acceleration. I understand that the above fixes may address that as well so I'll keep my fingers crossed.
Rockcrusher, here are pics of what I believe to be the power relay. It's above and behind the ICM. The pictures are taken looking straight in from the glove box opening.
Attachments 84.7 KB Views: 1,073 99.2 KB Views: 748 7,567 posts · Joined 2004. about 1.4k to 1.5k in park. about 1.2k to 1.3k. . rpm down to 1.0k to 1.1k I'm getting closer to spec.
Hope this is what you meant .
Vacuum, Vacuum, Vacuum. Can't over-emphasize the importance of a tight system.
Where is it again that we are going. And why are we in a handbasket? Show more replies 32,795 posts · Joined 2008 Pull the relay and post the MB part number. I don't know what you a describing as a power relay. 1,032 posts · Joined 2011I agree with Rowdie, probably the Idle Control Module. Repaired/replaced 3 times in 30 years on my car. Verify that it has the same part number and install it, worst case: You have a spare ICM for future use, best case: Your idle RPM is down to 650, and you have not spent a lot of time fixing it.
Don't think the temp sensor is your problem, but easy to check, open and short the wires, check for change in rpm.
4 posts · Joined 2022I am in the middle of dealing with the same problem with my 1982 380 SL. I found the attached troubleshooting helpful, except that when I started the troubleshooting (p60), I did have 12 V to the ICV. Oddly enough, even though I had a 12V reading, the valve did not operate. Before replacing the ICV, I tested the ICV with direct 12 V and it operated. This led me to believe that even with a 12 V reading there wasn't enough amperage. I continued to p 61 and jumping the terminals at the ICM the ICV operated. This also mean that the OVP relay is operational. I would assume that with the ignition in the ON position, if I plug in the ICM I should hear the ICV operate. This leads me to believe the the ICM is the culprit. With the ICM connected or disconnected, the car starts fine, but as soon as it warms up it idles at 1500 RPM. I hope this information helps and if anyone can chime in on my troubleshooting, it would be greatly appreciated. Can anyone recommend a reliable ICM remanufacture?
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