Some further notes:
The open throttle switch is non-functional and giving a reading of 50K ohm all the time, without change on any throttle position. The idle contact, the pin#2 works fine, closed (2 ohm) and opens as soon as you touch the throttle.

If the ECU sees 50K (which is pretty high resistance) as contact made, there is an issue.

Went to our parts car TPS (throttle sw) and it is open ckt all the time. So I am looking into that one at the moment.

I'll give the O2 trick a try as well - I didn't know that you had to be one-step ahead of the ECU to fool it.

Thanks a lot for the help. I think we are on the right track here.

PS I did swap ECU's and MAF's - exact same behavior.
Because unplugging the MAF = decent running, this tends to rule out ignition faults (like 4 cyl op) and points to sensors that function when the MAF is operational.

 

Did you check the idle switch function als o when engine was warm?
Heat might affect the cable adjustment enough to trip the idle switch if the cable is tight on the limit when cold.

/Peter

 

Soldered up the O2 sensor leads tonite and she's running real sweet now.

The O2 was connected with butt connectors, quite corroded. This came apart for the trans job I am pretty sure.... but have to talk to (nameless) first before labeled guilty.

Anyway, all three "green" connectors were clumped together, not attached to the actual O2.

I've been running various 928's (87, 90, 93, 82, 87, 88, 83) over a 10 year period and never really had an engine problem. I have had fuel pumps go and idle stabilizers stick. This 90 we had to replace the MAF a couple of years ago but that's about it.

The throttle switch WOT is also defective. I was successful in fixing the one from our '89 parts car by injecting electrical cleaner.

Thanks for the replies - they did the job.

 

if your going to go to the trouble of replacing the tPS switch it might be better to replace the switch with a new one , congrats of finding the O2 wires fouled up, thats just my thought

 

Appreciate the follow-up post; glad you fixed it!