This may be a stupid question, but my truck is the first automatic vehicle I have ever driven, so this may be completely normal..

Anyhow, when I put the truck in park and leave it running, it idles at between 1000-1200rpm.. and every 15-40 seconds, it will rev itself like 300-400 rpm is all..

Is this normal or no? I just cleaned the TB and TB Elbow and replaced the IAC Valve yesterday. I know for a fact it did this idle rev thing before I did that, but today it seemed like it did it way more often, but that may be placebo effect of me having done the work I did yesterday..

Any help?

 

Did you reset your pcm? if not it could be confused and needs to relearn whats going on.

 

Check for a vacuum leak.

 

Only way for idle to change is extra air 'after' the throttle body.
Vacuum leak, IAC moves futher open, loose mounting bolts, gasket etc.
A change in fuel does not result in very much of a change in RPM if it cannot be burned with exta air.

 

So then I take it that it is not normal? hah..

I didn't notice any broken or punctured lines or anything like that when I was cleaning the TB... the IAC is brand new like I said, Hmm..

 

You sure its not just the AC compressor kicking on and off at idle? That's what mine does.

 

Don't think so.. I didnt have the AC on..

And today, I drove it 150 miles, for approximately 10 hours and it didn't do it at all today.. And the only difference between yesterday and today was that yesterday was like 85 degrees outside and today was like 60... But I don't see how that would effect anything..

I dunno. I'm confuzzled.

 

To make sure that your ac dosen't kick on you have to have you heating system complatly off, so if you still had your defroster on it will still kick one for a little bit.

 

Nope.. didn't have any air on. Had the selector in the Off position.. Just had the windows down

 

I had a problem with the vacuum tube on the fuel pump, it was clogged to the point of it turning hard as cement. I remember my truck used to do the rev up/down thing you described, and I don't think it does it anymore now.

Easiest way to check if that's the problem is to open your fuel cap. If it seems like there's a lot of pressure in the fuel tank, and it hisses out at you when you open the cap, that's the problem.

-Ryan

 

My trusty ole f150 was doing the same is not normal as it just started doing it there was a small vacuum leak that I fixed and the choke was sticking as well I used 5.56 lube can on it and it stopped I would say yours is a faulty choke issue.

 

An 01 doesnt have a choke - it has fuel injection and a IAC.

 

101 on starting and idle;
The PCM pulses the IAC controller in response to the OX sensors feed back signal that control amount of fuel injected.
A closed loop function.
If the IAC is sticky and/or temp sensitive you will get varying idle because it can't smoothly control the air intake function.
What also happens is the OX sensors detect this and get into the act of varying the fuel and the whole thing becomes magnified and unstable.
Any other air leak that is subject to a varying amount will cause the same kinds of reactions.
For cold start; the temp of the air is sampled by the PCM thru the temp sensors at key turn-on and before the motor ever cranks over..
This sets up a program in PCM that richens up the fuel and opens the IAC wider for higher idle and adjusts the ignition timing. In about 45 second the Ox sensor heats up with help from it's electric internal heater to about 600° and takes over the normal fuel control, then the idle slows down to the normal 850+/- rpm and should stay nearly rock stable.
On FI motors there is no choke function.
A choke function uses engine vacuum to draw fuel. This is not needed in fuel injection where the fuel is force fed through injectors under pressure.
Any hunting , stumble, high idle after about a minute from cold start, is a fault.
This is the big difference between a carbed motor and FI system. Not even close for overall fuel control and performance when no faults are present.

 

^^^ Good explanation.

You might also try picking up some CRC cleaner from your local auto parts store and cleaning your MAF sensor. Good luck with it.

 

Hey all, I appreciate the replies..

The problem actually appears to have fixed itself, after that one day it hasn't done it anymore.. And that one day was the day after I replaced the IAC valve.. so I'll just chalk it up to a new part working better and the engine adjusting or some BS like that.. Idle also smoothed out since I replaced the PCV Valve.

Again, thanks for all the responses...