87 F150 Sharp rpm fluctuations and stalling

Jerad1389
Wed, 17 Nov 2021 19:01:10 +0000
Maintenance/Repairs

1987 F150 V8 302 automatic. 130k miles.

New iridium plugs (gap checked, all correct), wires (tested for resistance with fluke dmm), ignition coil good (tested with dmm), motorcraft distributor cap, rotor, newer injectors, new fuel pump relay, new computer relay, fuel pressure is where it should be (when cranked during crank/ no start condition), newer fuel pressure regulator, new motorcraft fuel filter, pip sensor in distributor changed a few years ago, fuel pump changed 2 years ago, battery good, compression test read between 165 and 180 on all 8 cylinders, newer motorcraft TPS, new motorcraft IAC valve, alternator tests good, ignition module relocated and module itself tested properly. All parts have less than 10k miles on them. It was driving alright with a slight miss, been trying to find it. Today it started like always, idled down to about 750rpm, fluctuated a bunch of times and stalled. It wouldn’t start back up. Today, it would idle smoother for a while, then out of nowhere it will fluctuate like and stall. It’s as if I’m quickly and randomly revving the engine. When it stalls, the key is still on and the fuel pump relay primes a few times.

Recently, I was trying to find possible causes for poor gas mileage (10 mpg) and researched the factory idle reset. It had been idling about 1000rpm and the book says 650rpm, so I got it to 650-700 (followed directions, unplugged IAC, set the screw, etc). Also set timing properly (removed spout as directed). I vacuum tested one of the ports on top of the intake manifold and it registered and held (with minimal movement) in the green/ normal range. Tested 3 injectors that were quickly and easily accessible and they were fine, but I haven’t checked the other 5 yet. Started, RPM shot up, stalled. Repeated 3 times just the same.

8 posts - 5 participants