(Fixed!) High Idle

I might have defrost on. Sometimes I had AC on and sometimes I didn't. idk it seemed like the idle is higher than I've ever seen with AC and defrost on. It's like 1800 once it's warmed up. I'll try idling with those definitely off.

For TPS voltage, Techstream does not show me. I'll check my bluetooth OBDII reader and see if that one will provide me TPS voltage.

Is my MAF reading good? I know MAF at idle is normally lower than my reading. MAF usually rises with RPM. Given my idle is higher than normal, I suspect my MAF is fine, and it's just slightly higher than normal idle due to my idle being slightly higher than normal.

Yes, I'm also starting to suspect the IAC is bad. I cleaned the TB and let the gunk drain into the IAC. I then took the IAC off and cleaned that as well. I didn't blow compressed air into the IAC for fear of damaging it. It's possible I never fully flushed out the carbon buildup that was on the throttle body and IAC which all made its way into the IAC passages. I'll try actuating the IAC with a 12v battery and see if it opens and closes well.

It's also possible I cracked my head. I read one report where the person found their high idle was due to a cracked head. Fingers crossed that's not it for me. I did just disassembled my cam in the wrong order (I left one cam journal totally tight and loosened the others completely, and also the cam sprocket was still connected).

Will the idle normally settle down before the ECU does all its systems checks? My system still has some checks outstanding. For example, the catalytic converter requires a fairly lengthy amount of driving, including some highway, to get a pass result. I haven't done any highway driving yet.

 

MAF will be high with a high idle unless it's due to a vacuum leak.
Have you checked that the IAC moves freely with no binding or sticking?
Idle is generally dependent on engine temperature and load, ususally idle at operating temp is 550-800.

 

I doubt you cracked your head, the iac is now suspect. Don’t worry about the cams, you didn’t damage anything. I would take the throttle body back off, (get an iac gasket kit) and take a close look at it. While doing this remove and clamp the battery cables together. When done, make sure all accessories are off, start it and let it idle 10min. The idle will be quite high but eventually should slowly drop. Turn it off, give it a little while to cool then start and drive it under a range of conditions. You can find more info on that by using the search feature

 

It was the IAC. Resistance tested fine and it even showed some values in tech stream which looked sane.

got the IAC off the truck and hooked it up to a 12v (power tool) battery per the FSM. The IAC would not open or close.

I suspect when I did a half ass job of cleaning it I created a paste of carbon. Once it dried I suspect the carbon paste glued the metal part of the IAC that opens and closes. I cleaned the part and it would open but not close. I had to clean it a lot more and then it would close a little. Even more cleaning and now it closes the correct amount (which I believe is mostly but not all closed). One tip if you go this route is hook up the battery to help it close, then use one a tip to rotate it closed, and use another q tip to wipe it. I was a little nervous to destroy the motor but I didn’t have much to lose since mine was a brick if I couldn’t fix it. After I got it moving nicely I sprayed some cleaner and actuated the motor both ways a million times.

Lesson learned, if it works, maybe don’t touch it (unless you don’t mind getting a replacement). And if it doesn’t work, the metal part that moves has to be shiny metal, no carbon allowed at all.

Honestly I’m surprised mine worked before I cleaned it with so much gunk.

Also I can see daylight on my throttle body. It seems like it may need to be adjusted to be able to rotate closed just a hair more closed. I’m going to leave my throttle body as-is since I suspect the IAC was the cause of my problem given it was totally stuck.

the pics show after cleaning the IAC. I think I cleaned the throttle body a little more maybe after the pic, can’t recall.

I’ll confirm the fix worked later this week. I want to get a gasket for the IAC since mine is looking a little tired. I have to wait for that part.

 

Great job! We knew you could do it! Hey, you need to tighten up that plate though while you have it out. Move the throttle stop so it’s just fully shut under its own spring pressure.

 

Awesome!

Also on the iac cleaning, to really get it clean, sometimes you need to remove the two screws in the plastic portion and separate. I've seen a few threads on here where people have shelled out the big bucks for a replacement when a through cleaning most likely would've worked.

 

Thanks, yes I considered taking it further apart. I wanted to work progressively more aggressive to avoid the risk of breaking it or accidentally reassembling it wrong. I did consider taking apart all the plastic (if possible) to see if I can get it down to just the metal. If I could get it to just the metal than maybe I could toss it in the ultrasonic cleaner.

 

Thanks! Which screw should I adjust? It seems like a lot of the screws are set at a position where there’s free play in the assembly (either free play at the screw or in the linkage)

 

If it's working I would leave the throttle adjustment alone unless it becomes a problem.

 

Mines a 2.7.... one of those is physically holding that plate open right now (that’s not wear) perhaps one with a molested paint mark because that plate should be shut thus why you have an iac circuit.

 

Smart thinking.

 

Guys, she’s running like a brand new truck!!! Omg what a journey. Thanks for the tips. So yes, confirmed, stuck IAC was the cause of the high idle.

Now with all that I’ve done, the truck idles lower than it ever has in my ownership. It’s so quiet and smooth at idle, I can’t believe it. It does have new injectors, plugs, wires, coils, valves adjusted, air filter, etc etc. hard to say what all contributed but it seems less keen to stall despite the super low idle. I hope this truck lasts a while longer

Video of idling warmed up. Pardon the windshield wiper and rain noise. It’s raining here.
https://youtu.be/gHpKPOhETXg

 

Glad you got it fixed! I just fixed my bad idle yesterday too. Same thing, bad iac valve.

 

bad idle valve causing idle problems. Who woulda thought haha

 

The truck shifts better now than it ever has. The little things keep adding up. I just wish I had owned this since new so I knew what it was supposed to run like.

 

How long after you cleaned the IAC did the idle go back to normal? Right away or did it take a few days?

 

I cleaned it twice. The first time I didn’t clean it well and no amount of time would have fixed it. The second time I got it working perfectly (I tested by using a battery to activate the rotating silver drum/cylinder) and the idle was fixed quickly after that. I don’t remember how long but I think it was the first drive

 

Ok interesting, I just had a shop replace my IAC and they told me to wait a few days for the idle to relearn, since there's no noticeable difference right now; not sure if theyre just saying this, or if it's actually fixed the issue.

 

There’s some truth to the relearn, give it some time, but it may not be the fix, lots of causes for high idle.

 

MAF sensor cleaned, throttle body cleaned, IAC replaced, no codes, idle cable seams fine, I'll give it some time but running out of causes.