1988 Ford F-150 Lariat XLT 4X4 Engine Troubles

NICK978

MEMBER
1988 FORD F-150

High, recently I have been noticing a recent decline in my trucks performance. Its a 88 Ford F-150 Lariat XLT 4x4 with a 302 5.0 litre fuel injected engine, and a 5 speed tranny. Its been hesitating and backfiring many times inside the headers while going down the road or accelerating. I thought it maybe the Idle air control valve because when I plug the wire back in, it does worst than if I just unplugged it, also with the IAC valve plugged in, it has a very high idle at like 1500 to 1800 rpms. I wanted to know someone elses opinion on whats wrong with it before I spend 70+ dallors on a new IAC valve.
Thanks

2 Replies

INDYUKE

MECHANIC
416 POSTS

Go to the junkyard and buy an IAC valve off a ford taurus for $5. They're identical. If it doesn't fix your problem, take it back. :Roll:

On another note, I have run into that problem. Ironically it was with an 88 f-150 as well. Not saying this is your problem, but mine turned out to be a bad coolant temp sensor. It read the engine as never warming up, so it kept the cold idle speed (which is significantly higher when the engine is warm than when it's cold) as well as never letting the engine go into closed loop mode. So the oxygen sensor was never referenced in order to correct the cold enrichment fuel trim it was constantly running on, thus a lot of unburnt fuel was being dumped into the exhuast system where it ignited as it pleased. Very annoying.

Just out of curiousity, the oxygen sensor is hooked up, right? I know some guys who unhook them just to get the engine to run richer. Bad, bad, bad.

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Sunday, August 19th, 2007 AT 2:47 AM

NICK978

MEMBER
4 POSTS

Yes, the oxygen sensor is hooked up, but I haven't checked to see if it needed replaced. Ive already replaced the coolant temp. Sensor in efforts to fix my faulty temp gauge to no avail. Ive attempted to time it with a timing light, but found out I need a probe or something to time it correctly, since its such a high idle, the timing must be off a bit. Im not sure if this is normal, but also at high rpms such as 3000 to 3500, the truck begins to smoke. Also, if ran really hot, the engine will smoke from the bottom of the fuel injection system that mounts to the intake manifold, dunno if that has any signifigance though Thanks for the info so far too

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Sunday, August 19th, 2007 AT 3:51 AM