Temperature related problem?

[JMitchell]

I recently posted a temperature related problem I have been having with my 84 911 Carrera.

Car runs fine for about 20 minutes. Then without warning as though a relay switches the car starts to run rough, backfire and cough. Seems to be on the lean side. Will not run smooth above idle. after it cools for a few hours the car runs fine again until normal operating temperature.

Could this be a computer issue? Is there a shop that could bench test mine?

These are the items I have replaced:

DME relay.

Cylinder Head Temp Sensor.

Cap and Rotor.

Disconnected the O2 sensor.

I live on the Big Island and the local shop is not familiar with 911's. Would like to trouble shoot myself. Any ideas would be appreciated.

I do have a chip installed. Car has been running fine for years with this chip.
Thank you,

John

[SchnellSchweitz]

STARTERS (Easy check):

1) See if your head studs are loose. I have heard of broken or loose cylinder head studs creating a vacuum leak once warmed up. Vacuum leaks cause lean conditions and higher temps. Do this by poking your finger into each head stud hole and wiggle the stud.

[DRACO A5OG]

Find a 3.2 buddy and place your dme into his to elimnate that as a culprit.

[kodioneill]

Check the reference and crank position sensor resistance when hot.

[JMitchell]

Originally Posted by kodioneill

Check the reference and crank position sensor resistance when hot.

Good call.

[JMitchell]

Originally Posted by DRACO A5OG

Find a 3.2 buddy and place your dme into his to elimnate that as a culprit.

Plan on shipping mine to Steve Wong to have it bench tested.

Thanks.