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uwanna uwanna is offline
Join Date: Jan 2009
Location: Marietta, Ga (Atlanta)
Posts: 2,914
The symptoms you mention can be caused by a bad connection to
the Cylinder head temp sensor, here's a post I put up when I had
a similar problem, good luck:

964 hard/no start problem
Went to start my '80SC with 964 3.6 transplant yesterday and had
a starting problem. Motor would crank and fire off but would not keep running. Found if I modulate the throttle, I could keep it running and after taking it for a drive it would start AOK, but the idle was a bit up and
down i.e. not steady.

First thought was a bad cylinder head temp sender, so I pulled the
plug at the engine and the ohm reading was right on for a warm engine.
I then let the motor cool over night and checked the temp sensor reading at the motor. It read right in spec at 3.6K ohms. So the sensor seemed OK.
I then used the trouble shooting chart below and pulled the
DME cable connector off the ECU and tested the test points at the connector. Everything tested again at the correct 3.6K ohms.

I then got out my can of DeoxIT D5 connector cleaner and sprayed
the test points. Hooked it all back up and VOILA she fired up just like normal.Everything is now working perfect!

According to the trouble chart, if the ECU doesn't see the correct
resistance it enters "limp home" mode and will run, just not correctly.
It seems that was the problem I was experiencing. So a little DeoxIT
D5 performed like magic and fixed it. I have never experienced any
connection problems with the DME/ECU connection before, but I now think I will pull the connector off again and spray all the connections.
Thank god I had the service manual or I still would be scratching my head!

'80SC Widebody 3.6 transplant Anthracite "The Rocket"
Long gone but still miss them all:
'77 911 Targa, '72 BMW 3.0CS Coupe(finest car I ever had!)
'71 911T Coupe White, '70 911T Coupe Blue
'68 911 Coupe Orange, '68 911L Soft Window Targa
Old 09-10-2018, 11:49 AM
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