Got a 95 351 F350 5 speed that idles to high, don't know how high as I don't have a tac. I've replaced the TPS, IAC, neither helped. Replaced all the vacuum lines that I can see. Still idels high. Funny thing is when I unplugged the IAC it went back to normal and ran fine. Also the check engine light came on right after I changed the TPS which involved removing the throttle body etc. I know I need to get the codes and I will I just wanted to know if anyone had any ideas or had this happen to them before and knew of a solution. Thanks.

 

Sounds like someone messed with the screw on the TB. This in a NO, NO.

The engine should die (or very close to it) when the IAC is unplugged.

 

Well I can I say I've never touched since I've owned it since 1997.

 

Then you have a vacuum leak somewhere.
Time for a smoke test.

 

^x2...don't touch the idle screw. If you think it is possible someone else adjusted it, then you should set it. There is a certain procedure for this so if you just try to adjust the screw yourself, you will want to know the procedure.

And, just like Subford said, the other possibility is a vacuum leak. If you think your lines are OK, another possibility is that the leak is in the intake (gaskets).

 

Yeah I see no reason to touch the screw because my problem has just started happening.

 

Well you said the truck still runs when you unplug the IAC. As Subford said, when you unplug the IAC the motor should die (or just about die). The fact your motor stays running indicates it should be adjusted.

Pull the codes FIRST. Fix any issues there. Then look at adjusting the idle screw properly.

 

Just clarifying; the engine not shutting off with iac unplugged is not an indication of the screw needing adjustment. The screw can be adjusted, but is a last resort only, or to compensate for something that's been changed. Good advice otherwise, just didn't want him to jump to adjusting screw before finding and fixing vacuum leak.

 

Ok I pulled the codes and it gave me a code 22, MAP (vacuum) or BARO signal out of range – MAP, and a 61 which I booked up and is something about the ETC which I know has nothing to do with the high idel, can a bad MAP cause a high idel? Tried using the old cigar smoke test for vacuum leaks as I breath in smoke through the break boster vacuum line, could not see any smoke anywhere. Is there a better place to try the smoke test? Then I used carb cleaner (I know I should not but trying to find answers) and sparyed around no increase in idel. Any ideas? Thanks.

 

Spraying ether or some other highly combustible chemical is just fine to find vac leaks, you'd have to discharge the entire can at once in order to make a fire, it evaporates too quick.

Map definitely causes running issues, so I'd start there and test it. It's possible your engine is too worn and doesn't generate enough vacuum at idle as a result, so hooking up a vac Guage is a good idea as well.

 

The engine may have been cold for the 61 code.

We need to know where you got the 22 code from as there are three different answers for the 22 code. Did you get it from KOEO (DF1), CM (DF90) or KOER (DF7).

 

I have no idea, I simply jumped the ECT and then counted the blinks.

 

I would expect three digit codes on a 1995 truck. Perhaps the 5-speed transmission is why it has two digit codes?

 

Sorry I missed that. Yes the 1995 F-series all had three digit codes.
1994 was the last year of the two digit codes for the F-series.

 

So I was doing it wrong? I need to have a 3 digit code instead of just 2?