I’m working on a 1987 Ford F150 that’s cutting out at speeds above 45mph. The ignition system and fuel pressure checks out OK, but it still cuts out at speed. Today I noticed a new symptom and a rather bizarre one at that. If you slam a door or hood, the engine speeds up 500 rpm and then settles back down. Any ideas?
Loose or corroded electrical connection, or loose vacuum line or gasket.
Try poking, prodding & tapping under the hood.
If the engine idle speed changes from the act of slamming a door or hood, the problem might be with Idle Air Control valve.
Fords are notorious for this.
To see if that’s the problem, with engine at operating temperature and idling, take the handle of a screwdriver and rap on the IAC valve. If the engine idle speed changes replace the IAC valve.
But stalling at speed I think is totally different problem.
Tester