Idle Control Unit Board and associated components
01-17-2019, 11:38 AM
#1
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1985 500 SEL w126 (11/84) - 1991 560 SEL w126
Idle Control Unit Board and associated components
Hi Folks,
I have been stuck on this high idle and finding information about the actual ICU and the ICV functionality in detail for a while. I have been reading through like crazy but while bits and pieces of the information are helpful, I cant find specific information or specifics for my particular issues. There's a thread on here that shows a close up of the ICU board and replacing three transistors. It was hard finding the exact matching pieces but I found them from Germany. There is another board pic, looks like it shows one of the resistors changed out for a switch or something that two wires are soldered in going somewhere. There was no description of the pic. Anyone know what that is?
I have tested the ICV by applying 12vdc directly and find that it drops my rpm to a stall. I am confident that the ICV is functioning. I have two ICU's, one is original from vehicle and the other is a used unit. Both have same part numbers - 002-545-33-32. I removed the back of the wire harness on the ICU to measure readings at the pins.
Current original ICU
PIN:
2 = 12v (battery voltage)
4 = GRD
6 = 12v (bv)
8 (not sure what to measure but there is no voltage)
pins 1 and 5 control ICV
1 = (no voltage to ground or to pin 5) but I get battery voltage to + terminal as if pin 1 were a ground
3 = 6.25~6.4 volts
5 = same as pin 1
7 = same as pin 8
9 = same as pin 8
The other used ICU that I tried had the same pin results except that across pins 1 and 5 there was .25~.30 volts.
Still have the high idle. I checked all the temperature sensors and grounded/jumpered them to be sure. Looking at other suggestions, I also replace the three transistors on the original ICU board and re-soldered what looked like a couple of cold joints, there was no change. It seems that the ICU is the problem, I want to verify and repair it somehow.
It would be great to have a detailed component schematic of the ICU so I can continue to test the parts on the board plus it would show me the functionality of the board. My scope is down right now but I can follow through with some other component testing. I have not found a reasonable price for a ICU yet, otherwise, I would just purchase another. I have two ICU's here and no reason why I can't get one to work, I hope. It would also be great to find or get an understanding of how the ICU and ICV work together and how the other surrounding controls are integrated in functioning all together.
Does anyone have any ideas, information or direction to share?
Much appreciated !!
'85 500 SEL 117.963
I have been stuck on this high idle and finding information about the actual ICU and the ICV functionality in detail for a while. I have been reading through like crazy but while bits and pieces of the information are helpful, I cant find specific information or specifics for my particular issues. There's a thread on here that shows a close up of the ICU board and replacing three transistors. It was hard finding the exact matching pieces but I found them from Germany. There is another board pic, looks like it shows one of the resistors changed out for a switch or something that two wires are soldered in going somewhere. There was no description of the pic. Anyone know what that is?
I have tested the ICV by applying 12vdc directly and find that it drops my rpm to a stall. I am confident that the ICV is functioning. I have two ICU's, one is original from vehicle and the other is a used unit. Both have same part numbers - 002-545-33-32. I removed the back of the wire harness on the ICU to measure readings at the pins.
Current original ICU
PIN:
2 = 12v (battery voltage)
4 = GRD
6 = 12v (bv)
8 (not sure what to measure but there is no voltage)
pins 1 and 5 control ICV
1 = (no voltage to ground or to pin 5) but I get battery voltage to + terminal as if pin 1 were a ground
3 = 6.25~6.4 volts
5 = same as pin 1
7 = same as pin 8
9 = same as pin 8
The other used ICU that I tried had the same pin results except that across pins 1 and 5 there was .25~.30 volts.
Still have the high idle. I checked all the temperature sensors and grounded/jumpered them to be sure. Looking at other suggestions, I also replace the three transistors on the original ICU board and re-soldered what looked like a couple of cold joints, there was no change. It seems that the ICU is the problem, I want to verify and repair it somehow.
It would be great to have a detailed component schematic of the ICU so I can continue to test the parts on the board plus it would show me the functionality of the board. My scope is down right now but I can follow through with some other component testing. I have not found a reasonable price for a ICU yet, otherwise, I would just purchase another. I have two ICU's here and no reason why I can't get one to work, I hope. It would also be great to find or get an understanding of how the ICU and ICV work together and how the other surrounding controls are integrated in functioning all together.
Does anyone have any ideas, information or direction to share?
Much appreciated !!
'85 500 SEL 117.963
01-17-2019, 07:09 PM
#2
Out Of Control!!
I think you have to understand the electromechanical aspect of the IAC before you go screwing around with the idle control module which you no doubt have ruined
01-17-2019, 09:21 PM
#3
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Join Date: Dec 2018
Location: The Lone Star State
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1985 500 SEL w126 (11/84) - 1991 560 SEL w126
01-18-2019, 08:05 AM
#4
Out Of Control!!
There is only one reliable and correct information database on your older MB control units and that is MB WIS---all others are the FUYAA scenario.
