911SC with 964 engine idle bouncing at start up

[yelcab1]

I am trying to solve a cold idle issue on a 82SC with a 92 3.6L engine from a 964. Its idle is bouncing wildly up on cold start up and after a couple of minutes, it settles out steadily at 850 RPM and then runs fine.

So far, I have exhausted all things known to me.

1. Idle Valve cleaned, no difference.
2. Idle Valve swapped with a known good one, no difference.
3. Fuel pressure rock steady at 50 psi.
4. Smoke test, no intake leak, no vacuum leak
5. Idle switch works, well adjusted, clicks when throttle cable is off idle, changes resistance when switch is activated.
6. Swapped out ECU for one from a 89 964, no difference
7. Swapped out vacuum switch at the intake manifold, no difference.
8. AFM removed, cleaned, and it seems to solve the problem, and then it came back after a couple days.
9. AFM board replaced with unit from China, it does the exact same thing with no difference.

I have the Durametric but it does not do Idle Adaptation.

I will try to find another AFM and see if that makes a difference.

Does anybody have any other suggestions?

[991gts6s]

o2 sensor >??

[yelcab1]

Originally Posted by 991gts6s

o2 sensor >??

Already replaced with a new one. No change.

[yelcab1]

So the long battle seems over.

It was the Air Flow Meter that was tampered with to be way too rich and the car was hunting trying to adjust to it. After I opened up the top, adjusted the toothed disc by 15 teeth CW, the bouncing idle completely disappeared.