Erratic Warm Idle Finally Solved
 

I have been chasing a rough warm idle dragon for literally years. I worked around it through various methods but I never had a smooth running car, even after a complete rebuild.

I have fixed or checked every possible vacuum leak.
I have replaced the fuel injectors.
I have replaced fuel filters.
I have check fuel pressures.
I have replaced wires and plugs and had the distributor rebuilt.
I have checked WUR, AAR, AAV.
I have checked the O2 Sensor Relay.
I have pulled and check the air box for separation
I have fine tuned the mixture at idle... perfect at warm up and warm, the rough idle could not be corrected.

I have even resorted to checking the cupboard for more 12 year old Scotch to give me the strength to keep at it.

Well... I finally found the issue and I wanted to share it because I am sure I am not the only one with the issue.

I replaced the CAT in preparation for an upcoming smog test and decided to replace the Oxygen sensor at the same time. The new Bosch unit did not have a connector, so I snipped off the old connector to attach a new bullet connector and there it was... there was the issue, such a simple thing and I never thought about it being an issue.... wait for it...

My 1980sc uses a Coax for the oxygen sensor lead from the ECU. Outside is grounded shielding, inside is the positive lead. Some jacka$$ long before I bought the car stripped the wire of the coax and put on a new connector using both wires of the coax.. shorting out the two wires. The Oxygen sensor never could send a signal to the ECU.

After sobbing like a little girl (other CIS owners can appreciate)... I carefully separated the coax wires and clamped on a new connector. Vvvvrrooooommm!

Well.. the car is so smooth and quiet now, I thought I stalled it this morning because I didn't hear or feel the engine with the radio on.

Now with all my free time I may start listing all the parts I have replaced on ebay!

Sweet! Great job.

Just talking. I think the O2 sensor sent a signal but it was off the scale (one way or the other - rich vs lean) causing the Lambda box to try to correct a totally bogus signal.

Now you have the opportunity to dial it in.

Just for discussion, I think the 1980 box is morphed from 944 box. In 81 it got a 911 number. There may be an upgrade from 81 to 83, maybe?

It's not an ECU engine management box but it's the best CIS had in the later SC's.