Something is loading down the engine while the AC is on. As always 1st check the battery & alternator voltage. Next I would start looking for a vacuum leak somewhere in the CCV system. This could be a cracked vent pipe, or a bad diaphragm on the CCV valves. I would also check to make sure the oil cap & dipstick are both firmly seated.
Yes that would apply to the 650 as well. If you carefully pop the caps off, you can inspect the diaphragms for damage. They are easy to remove & inspect. I would also inspect the CCV vent tubes for cracks. Be careful moving them around. If they are old they can crack easily, & cost around 85.00 each.
Did you check the voltage to make sure the battery is ok? Have you used INPA to see if any cylinder is running rougher than any other? It is a little early for spark plugs, but it can't hurt to see what the plugs look like.
If you go into INPA & connect the car, run the analog values on the engine. It will show you a graph on each sensor, & cylinder. Look at the post by Tripleblack, he has some INPA graphs in his post. If INPA acts funny, keep pressing the keys to you get your values. I do not know why ISTA did not incorporate this into its program, or I do not know how to get to it?
I would try reloading INPA, & install in English UK I think. Sometimes crossing different versions can cause this also.
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