I would make sure the basic adjustments are made at the throtle body so that you know the micro switch and full throttle switch are set correctly. I doubt the O2 sensor is the issue. I would lean towards the Cylinder Head Temperature sensor or a good vacuum leak. From the sound of it, it runs terrible till the full throttle switch engages and the DME runs on the separately programmed full throttle map.
This is from another thread and shows how you can check the sensors with an ohm meter to try and narrow it down. It also would not hurt to look inside the often neglected distributor to make sure it is clean and weights are moving freely. Put a little oil on the felt pad.
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Originally Posted by E Sully
If it were a bad reference sensor the car would not even start. If a bad speed sensor I would think you would have problems throughout the rpm range. They can be checked with a continuity meter, last picture.
It runs good at high rpm, have you looked at the the idle micro switch and the full throttle switch to see if they are set correctly? These affect the fuel and ignition map the DME uses.
The old single wire temperature sensor can cause problems. Later sensors are 2 wire type.
The distributor may need to be looked at. Timing is set by the DME, but it still has centrifugal weights for rotor phasing. If the shaft has play it will affect timing. It is very easy to remove and reinstall, just get a new o ring.
Have you checked it at idle by removing the oil cap to see if the idle drops yet? If the idle does not drop you have a vacuum leak.
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