NEED HELP: mysterious miss
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Tuned
Joined: Feb 2003
Posts: 426
Likes: 4
NEED HELP: mysterious miss
I posted this previously on the 300CID forum. Having gotten no answer after a few weeks, I wanted to try again on this larger forum.
My truck is an '87 F250 with the inline 6. It runs great when warmed up but idles terribly. Here is the mysterious part. If I start the engine without touching the gas, it will idle perfectly until warmed up. If I touch the gas, though, it will begin to miss really badly and continue missing until the engine is warm. This engine has all new (or nearly new) sensors, IAC valve, plugs, wires, distributor cap and rotor. I have replaced the EFI plenum gasket, throttle body gasket, and EGR gasket and have cleaned throttle bore, etc. The computer says the truck is fine; it has set no codes.
Does anyone have ANY hint as to what might be going on? This is driving me crazy.
Thanks
My truck is an '87 F250 with the inline 6. It runs great when warmed up but idles terribly. Here is the mysterious part. If I start the engine without touching the gas, it will idle perfectly until warmed up. If I touch the gas, though, it will begin to miss really badly and continue missing until the engine is warm. This engine has all new (or nearly new) sensors, IAC valve, plugs, wires, distributor cap and rotor. I have replaced the EFI plenum gasket, throttle body gasket, and EGR gasket and have cleaned throttle bore, etc. The computer says the truck is fine; it has set no codes.
Does anyone have ANY hint as to what might be going on? This is driving me crazy.
Thanks
Senior User
Joined: Jun 2003
Posts: 352
Likes: 1
From: Tillamook, Ore
When it's missing, pull your plug wires off the cap one at a time. This will tell you if it's a certain cylinder. If you lift a wire and it doesn't change the way it runs, you'll know where to start. I had an injector go bad on my 351 and it acted like a bad spark plug.
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