OVP, vacum leaks, mis adjusted air flow door (disc, plate whatever you want to call it), idle switch (this is behind the airflow sensor housing on top of the intake), fuel mixture way off and coolant temp sensor come to mind.
Check the OVP per Gillys instructions.
Check the duty cycle (pin3 and ground, DVOM on duty%) mine run good at 55% idle and 45% @2500 with the a/c on. Fully warmed up, I take mine out and drive them a couple of mines then set them.
Check the idle switch, open with open throtte and closed with closed throttle if I remember correctly.
Then the fun begins, EHA ma draw tesing and hunting vacum leaks including internal leaks from sticking egr valves. My 92 wagon had a leak from a freeze plug in the back end of the intake causing it to fall flat on its face on accel and surge at speed, my old 88 wagon had several vacum leaks under the intake, a badly misadjusted a/f plate and a coolant temp sensor WAY out of range. I had a 90 model 260e with a badly frayed and corroded harness at the back of the head causing it to stall on accel and sometimes restart, other times play dead.
I never will forget the sl with the restricted filter in the tank, thing had a peice of what looked like saran wrap in the tank. (kids put all kinds of stuff in there playing in the garage. However this one had a screaming fuel pump when it sucked up the plastic and closed the screen.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.