1988 300E Duty Cycle Reading
 

I have a reading of 30.6 with ignition on engine off. Was looking for 70%. 1988 300E. Do I have a bad controller? Engine will crank with the idle control valve disconnected, but will die if rpm goes below 1500. What next.

With WOT does the reading change?

1988 300E Duty Cycle Reading
 

Yes it reads 80.7 with engine off wot. I think I might have found the problem in the coolant temp sensor. I disconnected sensor and I have the 70% Federal I was looking for. Also the engine starts much easier with sensor off, but will not idle. Thanks

Replace the temp sensor, plug back in, and try starting. I bet it will work. If not, check the idle control valve for proper operation.

1988 300E Duty Cycle Reading
 

the idle control valve clicks a couple seconds after ignition on. thanks for the help.

just to be clear what pins do you use to measure duty cycle, 2+3 or 1+3?

This is a trouble code. If I can find my FSM CD, I'll try to look it up for you.

pin #s
 

Its #2 and #3. pins for duty cycle .

1988 Duty Cycle Reading.
 

Hello Oracle12345 and mac, I used pin# 3 and 2. Also I replaced temp sensor with no changes in duty cycle. Found I only needed to remove the one sensor connector that goes to the KE control unit on the two pin coolant temp sensor to get 70.6% duty cycle. Wires from temp sensor check ok to control unit (N3) and ezl unit 4 pin sensor connector. Will start easily if temp sensor unhooked and idle control valve removed from hoses. But must run at least 2000rpm or engine labors and stalls. Thanks.