Well I bought the super clean 1995 F150 this weekend. Its an ext. cab long bed with a 351W automatic OD.
The idle was high at about 1500 rpm when I looked at the truck. After convincing myself it would be a simple fix and knocking the price down a bit I bought the truck. Yesterday as I entered the emmissions inspection station the idle was at a steady 2100 rpm. I tried to adjust the screw where the throttle cable meets at the top of the engine. Then I started messing with turning the distributor. No timing light or anything, just turning it to see what I could get it to do.
Well, as those of you who may know a little about this may have already guessed, I made things a little worse when I got the idle to slow down so I just put it back where it started.
I'm not real good at troubleshooting engines, even with detailed instructions. Are there some basic sensors or other things like PCV valves that I might go ahead and replace that could affect idle while I do a tune up and oil change on this motor?

 

About the worst thing you could do is to adjust the screw where the throttle cable meets at the top of the engine.

The curb idle and fast idle rpms are controlled by the Powertrain Control Module (PCM) and the Idle Air Control (IAC) valve. The Idle Air Control (IAC) valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow this device to effectively control the rpm.

Throttle bodies with sludge tolerant design are clearly identified with a yellow/black attention decal. This decal advises that the throttle return screw must not be adjusted counter-clockwise (backed off), as this will not reduce the engine speed but may cause the throttle plate to stick in the bore in the closed (idle) position. Backing out the screw may be required if the throttle body had been previously serviced (a plug in the throttle plate orifice may be present) or if the throttle return screw has been tampered with (TP sensor self-test output out of range), refer to procedure for details. The decal also advises that these throttle bodies must not be cleaned inside the bore, as cleaning will impair the sensitive coating. The sludge accumulation will not affect the throttle body idle air flow. (The cleaning procedure for the Idle Air Control (IAC) valve may still apply.)


To answer your question a high idle can be caused by any of the following:
1. a dirty, sticking or bad IAC valve
2. vacuum leak
3. binding throttle shaft or cable
4. PCV valve
5. TP sensor (Throttle Position Sensor)

The first thing you need to do is run a self test and then post the codes back here and we will try to help you. If you do not know how to run a self test go here:
http://fordfuelinjection.com/?p=13

Good luck

 

I ran the self test. I believe i'm getting a 12 and a 33 code. I did not understand how to interpret these numbers. (if I was even able to log them correctly in the first place)Speaking of the PCV valve, I bought one with the standard tune up stuff but I'll be darned if I can find it on the motor. I even bought a Haynes manual. I always tell myself I won't buy another one because they really dont have much useful or specific information. This manual proves that, if nothing else, they are consistent. God Bless all on this forum willing to help those of us in need of a little know how.

 

Well the here is what the code mean.
12: System cannot raise engine speed above normal idle.
33: EGR is not opening or is not seated properly.

 

The PCV valve is #87 in this diagram:
http://i54.photobucket.com/albums/g9...pcvvalve87.gif

 

i would start with code 33 if it is an egr code becuase your egr my be sticking open.

 

Aha! Hiding in the back! A guy at work told me it was in the back but I just didn't see it. Thanks for the diagram. That puts it into perspective. I'm digging into the idle problem tomorrow. Had to drive it to work for the last couple of days and used a ton of gas. The egr sounds like a good place to look. Thanks everybody.

 

It idles at around 1600 rpm. I started playing around with the IAC connector and found that when I unplug it it idles at 500 or 600 rpm. Seems to run well and sounds normal when IAC is disconnected.
I know the obvious answer is leave it unplugged..LOL..
Is this indicating that I need a new IAC valve? Or does this mean it is OK?

 

It sounds like the IAC is working OK.
But the engine should die when you unplug the IAC so this means you have problems elsewhere.

Maybe a vacuum leak, throttle plates not closing, ............

 

Thanks Subford. That does make sense. Others have said it should die after unplugging IAC. I guess I'll have to stop looking for a sensor or something and get down to finding a vac leak or similar problem.

 

I had that exact scenario. Truck started to idle at 1500-2000. So I unplugged the idle valve (engine died) and turned in the idle stop screw to keep it at 600 as a temp fix. I eventually got around to pulling the codes and got 123 - throttle position sensor. Replaced that and back to normal.
Maybe the reason your truck doen't die when you unplug the idle bypass valve is because you messed with your stop screw.

 

I'm going to sniff down that trail a little bit now. I almost bought a TPS tonight after Autozone pulled a 628 codefor me. It said something about TPS not matching up with air or something like that.
How in the world do you get to the TPS on the underside of the intake?

 

That fixed it! Replaced the TPS today and it's idling at 900 rpm which seems right. The transmission, which has been shifting funny even when it wasn't slamming each gear, feels perfect now. Shifts real smooth and when it should. It actually had a 121 code refering to the TPS. The 628 code had something to do with the tranny. Thanks for everyone's input. Weighing all info helped to save me from spending tons of money swapping parts.