90 FC Convertible: Thought I'd post since I wasted so much time troubleshooting. Car ran perfect when I dropped it off at a body shop to fix some rust around the windshield frame, but when I picked it up it had various issues with pulsating idle, would die at lights, when I turn it would die but seemed to run fine as long as I was driving giving it gas. As soon as I let off the gas it would try to die, but not all the time. Definitely unsafe. Weird, but I found two manifold plugs that had deteriorated and fell off. So look for these plugs since your car is around 30 years old. I put a few pictures but they are hard to see 1) one is behind the manifold near the firewall (see with inspection mirror), and the other plug right next to the ACV (see tiny red dot in picture between the air hoses). Both these plugs were missing - Plugged and runs perfect again!

were gone. Runs perf

 

Same here.. weeks of going CRAZY. Wound up being the plug behind the water pump... little metal clip was missing and wasn’t fully seated. Put a new clip and pressed in to make connection car ran MINT again.