230GE M102 duty cycle static at 40%
 

Hello All,

I have a 1987 230GE (M102) and it has a high idle (1200 - 1500 revs once warm) - via the duty cycle measurement I get a static reading of 40% when running which seems to indicate the potentiometer is the problem.

I pulled the old potentiometer and it had worn through the coating where the arms rub, I have also noticed it has a crack on the circuit board and there is no resistance between pins 1 and 3.

I ordered a new one (I have two replacements now as I assumed the first one I ordered was broken) and I read the correct adjustment is 0.7v between pins 1 & 2 - no matter how I pivot the potentiometer I am getting 7.0 to 10.0v at these pins. Idle is still high once the G warms up and I still get the static 40% reading on the duty cycle.

I found an old thread on this board where Durbo20vT had the same problem (high voltage on pins 1 and 2 and 0.7 voltage on pins 1 and 3) and it ended up being a short on the coolant temp sensor (2 pin) - I have looked at mine and don't see the same issue, the two wires are not shorted. I have moved wires around and also tried with various sensors uplugged to see if there is another short/bad contact without luck. I even swapped back to my old OVP relay without change in the voltage at the air-flow POT.

Engine has previously had a head gasket change, new EHA, ICV and OVP relay.

Any ideas?

Fixed! I was reading another forum and a user mentioned they had accidentally swapped the connectors during reassembly after a head gasket change (the connector for the potentiometer is the same as the throttle switch across from it).

Swapped mine and the potentiometer started showing the expected voltage on pin's 1 and 2 - a few adjustments and I am back to a smooth idle at the expected rev's.