Hey, guys. New here, but not to owning Blue Oval trucks.

I have a problem with my '95 F-150, extended cab. It's a 5.8, auto and 136,000. It runs pretty well and has been relatively trouble free until now. I am the second owner. It does have a couple mods I have done, K&N Generation I air intake and custom installed dual exhausts with low resistance cats.

What the truck is doing is that the idle will not drop back to where it should be. This is a very recent development. It definately idles way too fast at any temperature. I have replaced the air bypass switch (which the old one was badly carboned) on advice from a mechanic friend, but to no avail. I have also ruled out a cable issue or anything of the like. There are no "Check Engine" lights. There is a minor hesitation also, but I don't know if it is related. The truck is only getting 12mpg which seems a bit low. It is due for plugs which I am planning to replace within the next week or so along with a new set of Accel wires.

Other than the above, it doesn't run badly at all. Starts crisp and doesn't stall, etc.

I was hoping to pick a few brains before I have to resort to take it to the shop. I'm pretty much out of ideas myself and the POS Haynes manual is no help. We use it to tow our 24' travel trailer and it's going to Charlotte in May so I want it to be right. It doesn't get driven every day, but I don't let it sit too long.

I'd really appreciate any insight anyone has.

Thanks!!

 

Im not too great with the electronics in the trucks but I was having very similar problems with mine and it was the Throttle Position Sensor.

 

I'd suspect a vacuum leak. With the engine running, try unplugging the IAC valve. The engine should die. If it doesn't, the valve is either stuck (you replaced it so that shouldn't be an issue); or there's a vacuum leak. If it does run with it unplugged, get spray carb cleaner in suspect areas. The engine should die when you find your leak. Areas to check are the vacuum line harness, gasket between the lower and upper intakes (common for your symptoms), and lower intake gaskets.

Check codes too. Sometimes a code can be stored without the check engine light coming on.

 

I'll second the vacuum/air leak idea, but suggest you use an unlit propane torch to try to sniff out the source, test all gaskets, vacuum lines, vacuum resovoirs and the brake booster.

 

Thanks, guys.

I did first unplug the electrics to the IAC and the idle gets very slow but the engine still runs.

I'll check for the leak tomorrow after I get the new rad in my Jeep.

I never heard of using an unlit torch. How does that work? I do know about using carb cleaner.

 

It's the same idea, a gas is more easily pulled in than a fluid so it should make the problem easier to find.