Originally Posted by Graham
It sounds like a mixture problem as the car warms up. Could be the coil, but probably not if it happens after 5min.
Have you tried squeezing or blocking off the line from the AAV to the idle valve? After 5 min, the AAV should be partially closed. If it is sticking, it is same as having a vacuum leak. That will cause high rpm. The ECU will cut off fuel over 1500rpm at idle, so then you get surging. I would look at this first.
By setting CO at mid point, do you mean you have a CO meter and measured the CO or did you just set the potentiometer on the ECU to it's mid point? You really can't adjust the mixture on these cars without an exhaust gas analyzer or %CO or AFR meter.
On these cars, the timing should be more advanced. Best to disconnect vac lines and set it at about 30deg BTDC at 3000rpm. This should end up at 5-8 deg BTDC at idle with no vac retard connected. On the '75's, there are two lines to the distributor - one for retard and one for advance. Don't know just how to set that up, but check that the tiny ports in the throttle body are not blocked.
Finally, I would check the manual (available on-line
) sections 07.4 and 07.5 and go through the checks of all components. Especially trigger point operation ad TPS. Make sure the TPS reads zero ohms when throttle is against it's stop.
I am not exactly sure what you mean by "AAV". As far as CO goes, I was referring to the plastic dial on the side of the ECU.
Good news though. I found than when it runs terrible, that the #1 and or #2(depending on its moment) injectors aren't firing. There is no pulse at the pigtail. So if i am not mistaken, the problem is either in the wiring(didn't find anything wrong, even checked resistance from ECU pigtail and injector pigtails), ECU, or maybe the trigger points and or wiring from them to the ECU.
It seems strange that it is erratic and not consistent though.