My 88 5 speed sedan which is on loan to my Son has developed an issue. He called me 3 days ago and the car would only rev to around 1300-1400 rpm, it would buck, skip and pop if you tried to go any higher, if you let off on the throttle and bring it down to around 1000 rpm it would run fine. It was pouring rain out so I suggested it was probably wet, he limped home to his apt a couple miles away and had lunch, when he started it again around 1/2 hr later it ran fine. Yesterday he took it on a 2 hr drive and it ran fine on the way there, today when he started for home it did the same thing, he pulled over and shut it off, re-started it immediately and it ran fine all the way home and is running fine now. I will get the car in the next day or so to try to figure out problem. My 1st thought is the AMM might be going south, I have a spare everything so I can check everything by changing out components, my problem is if it is running fine when I get it I won't know if the component change out works unless I drive it for awhile. I got the car from a local junk yard (had a blown clutch) threw in a used disc and its been running fine for the last 13k miles. What would re-set by shutting the car off? could the fuel filter be plugged and when you shut it off the fuel drain back a little to temporarily relieve the pluggage? What should I check 1st or do I have to wait until it does it again?

81 Bertone intercooled turbo , 92 940 turbo wagon, 84 (300k) dl wagon mint, 88 DL sedan 5 speed, 90 DL sedan, 85 GL sedan, 89 5 speed dl wagon (winter beater)