I’ve been toying (pun intended) with the idea of replacing my IAC valve.

Overall, the truck performs well, but, every so often, I get a stumble on a hot start. Before everyone says clean the IAC, MAF, do the plugs and wires…etc etc etc. It has all been done in the last 12 months at most.

My idea of replacing the IAC is due to its age and the fact it is original to the motor which is getting ready to turn 224k.

Is this something that can weaken with age?

The last time I cleaned it, which was this past winter, I had a high idle for the better part of three weeks. It does now have inconsistent idle when hot, sometimes it’s as low as 550, and sometimes it’s up to 900-950.

Thanks in advance for your advice,

Scott

Did you clean your Mass Air Flow Sensor as well (MAF Sensor)?

I had similar symptoms even after cleaning my throttle body, IAC valve, and MAF sensor. I finally replaced my MAF sensor with a new Denso unit and everything returned to normal.

Did you not read my post?

Yes, I replaced my MAF sensor as well with a new spare. No different.

Yeah sounds like you've ruled out the things that come to mind like vacuum leaks, MAF, etc. Would a faulty TPS be related? IDK

I'll be following this thread see what you figure out..

I had a low idle issue that happened when hot would drop down to 500 RPM and stumble. From previous experience if the idle drops to the 400 level the engine dies. I bit the bullet and bought an OEM IAC from partsouq.com. I had tried an aftermarket "rebuilt" one and it ran terrible so I hoped a new OEM one would help. It did not, the issue persisted.

A high idle could be an issue with the butterfly valve or even the TPS.

on my old 2000 it had a sticky IAC valve. so when I clenaed it, I had it off the throttle body. sprayed heavy with cleaner, plugged it in and cycled the key several times, cleaned again, repeat. With throttle body off, I cleaned it super well as well. Reassemebled ( cleaned the maf and checked all hoses replaced PCV at the time too). Ive also read several times that cleaning a throttle body with the IAC still installed can dump garbage into them and make them worse.

My only problem then was a flat spot at about 55 mph, replaced TPS with OEM one, and that took care of the flat spot.
My experience with TPS ( on various cars) has been things like flat spots at certain speeds....not idle issuses. But I guess it could go bad and cause idle issues.

Yes I did read your post. I would clean it and verify that MAF its is within factory spec. Sometimes new parts are defective. Besides takes a few minutes and completely rules out the new part being bad and is cheaper then buying an IAC.

When I cleaned mine IAC on my 98 it ran funky for a week or two intermittent higher rpm etc. Then it cleaned out just like you stated your did before

P.S. Your Coils and spark plugs wires would have nothing to do with your rpm idle setting. The RPM is handled by your MAF and IAC.

Coils and plugs wires have to do with misfires issues etc.

Also maybe I missed it and if i did I apologize. Did you use OEM parts or Denso Parts from reputable dealers.

Also do you happen to have your AC or defrosters on as that higher idle maybe needed for the AC pump to run.

Mostly the TPS will throw a CEL Light when they start to go bad. :-) However, they can be checked for factory specs via the FSM to see if they are going bad or not.

Might wanna confirm your not dealing with a worn out throttle body shaft or flap.
Remove the throttle body from the intake and hold it up to a light source. The flap should be sitting in square in the intake throat. And pushing the throttle shaft around shouldn't disturb how even it sits.

I have tested the IAC and the throttle body in accordance with the factory service manual. Everything checked out within spec.

When you key on the pcm looks at the tps position and calls that idle. You can watch the tps position in live data with a scanner and see if the off throttle percent changes while you are driving.

A few here have had a new tps resolve their idle problem.


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My flat spot with my TPS must have been at idle. If I was coasting it would start trying to die on me (can't because the engine was still turning) and as soon as I'd come to a stop it would then die. Before that it was doing some very odd things like poor idle and holding the throttle open on the freeway for a second or so if I let off the gas.

Yes they were all reputable parts. OEM when possible.