SL/R107: Idle Control Module question
Thread Starter
Junior Member
Joined: Sep 2018
Posts: 20
Likes: 1
1992 300CE, 1983 380SL
Idle Control Module question
Sorry for long post, but not sure where to go with this...
Two weeks ago, I purchased a 1983 380SL with 111,000 miles on it.
Took it for a 150 mile cruise though mountain roads and ran nicely, if not a little underpowered. I know the 380 isn't exactly a workhorse, by my 300CE 6 cyl has more power.
Anyway, reading through paperwork that was given to me by seller, they took the car into an independent mechanic in May complaining of "sputtering" on takeoff.
Mechanic checked for good power and ground going to the idle speed motor and found good ground, but no power.
An additional test was done and found no power coming from the idle speed control unit. Paperwork says "tech needs to perform testing of ISC control module and module inputs to determine source of failure.
This sounds like it could get expensive, quickly.
Is there a way to chase this power issue at home, or is this something that needs to be done by a mechanic with the correct tools?
I guess I could just replace the idle control module for about $200, but I really hate just throwing money at problems... but at that price, that's probably an hour's work at the shop...
Two weeks ago, I purchased a 1983 380SL with 111,000 miles on it.
Took it for a 150 mile cruise though mountain roads and ran nicely, if not a little underpowered. I know the 380 isn't exactly a workhorse, by my 300CE 6 cyl has more power.
Anyway, reading through paperwork that was given to me by seller, they took the car into an independent mechanic in May complaining of "sputtering" on takeoff.
Mechanic checked for good power and ground going to the idle speed motor and found good ground, but no power.
An additional test was done and found no power coming from the idle speed control unit. Paperwork says "tech needs to perform testing of ISC control module and module inputs to determine source of failure.
This sounds like it could get expensive, quickly.
Is there a way to chase this power issue at home, or is this something that needs to be done by a mechanic with the correct tools?
I guess I could just replace the idle control module for about $200, but I really hate just throwing money at problems... but at that price, that's probably an hour's work at the shop...
Junior Member
Joined: Aug 2016
Posts: 24
Likes: 4
From: Danville, CA
1988 560 SL
Idle control unit
I had the same car, '83 380 SL and bought it, 20 years ago, with just about the same mileage.as yours. One thing your want to check is has it had the timing chain upgrade to a dual link chain. The original single link had chain had failures and the engine was then good for a boat anchor.
I replaced the idle control module with a rebuilt one from https://www.programainc.com. Good quality built from original units. I have used them a couple of other time for Ford and Toyota control units.
Another thing I learned was to use CRC contact cleaner and CRC Electronic Lubricant on all electrical connection I could find. Also replaced all the fuses and all rubber vacuum connectors. Also the usual stuff of muffler, fuel pump, lifters, power steering pump, heater valve.....
After all that it was a great car and I put over a 100k miles on it. I sold it when I inherited a 560 SL with 24k miles. Had to replace the timing chain and plastic guides in that car merely due to age.
I replaced the idle control module with a rebuilt one from https://www.programainc.com. Good quality built from original units. I have used them a couple of other time for Ford and Toyota control units.
Another thing I learned was to use CRC contact cleaner and CRC Electronic Lubricant on all electrical connection I could find. Also replaced all the fuses and all rubber vacuum connectors. Also the usual stuff of muffler, fuel pump, lifters, power steering pump, heater valve.....
After all that it was a great car and I put over a 100k miles on it. I sold it when I inherited a 560 SL with 24k miles. Had to replace the timing chain and plastic guides in that car merely due to age.
Thread Starter
Junior Member
Joined: Sep 2018
Posts: 20
Likes: 1
1992 300CE, 1983 380SL
Thx Bill. I guess I'll try replacing the ICM...
I've got a couple little issues... it has an aftermarket alternator and is putting out about 13.5 volts, which is making the dash light go on/off.
I had a voltage regulator lying around and swapped that in, but same result, so time to get a good Bosch unit.
I knew about the timing chain issue... Previous owners said that it had been changed, but had no documentation.
I told them I wanted to take it to Mercedes and have them put an inspection camera in through the valve cover to check it, or no deal.
They actually took it to an independent shop in town (that I've used in the past) and had the scope done... I have a picture of the dual chain.
And I think it needs shocks... it kinds of rolls in and of long turns (winding mountain roads), and it's pretty easy to bounce the rear corners of the car.
Overall, I'm pretty happy with the car. Top is good (not perfect), no cracks on the dash which amazed me, interior is great... although the seats could stand a little restuffing, and overall it runs pretty good.
I've got a couple little issues... it has an aftermarket alternator and is putting out about 13.5 volts, which is making the dash light go on/off.
I had a voltage regulator lying around and swapped that in, but same result, so time to get a good Bosch unit.
I knew about the timing chain issue... Previous owners said that it had been changed, but had no documentation.
I told them I wanted to take it to Mercedes and have them put an inspection camera in through the valve cover to check it, or no deal.
They actually took it to an independent shop in town (that I've used in the past) and had the scope done... I have a picture of the dual chain.
And I think it needs shocks... it kinds of rolls in and of long turns (winding mountain roads), and it's pretty easy to bounce the rear corners of the car.
Overall, I'm pretty happy with the car. Top is good (not perfect), no cracks on the dash which amazed me, interior is great... although the seats could stand a little restuffing, and overall it runs pretty good.
Junior Member
Joined: Aug 2016
Posts: 24
Likes: 4
From: Danville, CA
1988 560 SL
ICM
Sounds like you found a nice car. I can say that the electronics and charge system is very sensitive to voltage. My car had original alternator and regulator but sounds like similar electronic issues. I finally put in a Mercedes battery and problems ended! Evidently it was the compatibility with the charging circuit.
Enjoy it!
Enjoy it!
Thread Starter
Junior Member
Joined: Sep 2018
Posts: 20
Likes: 1
1992 300CE, 1983 380SL
Sounds like you found a nice car. I can say that the electronics and charge system is very sensitive to voltage. My car had original alternator and regulator but sounds like similar electronic issues. I finally put in a Mercedes battery and problems ended! Evidently it was the compatibility with the charging circuit.
Enjoy it!
Enjoy it!
This for the info, much appreciated!
