TBI Rebuild, now have high idle. I know what your thinking..

[2003Xtreme]

Long story short.. After disassembling my tbi on my 99 tbi 350.. I have a high idle.. I am sure your first thoughts are that I have a vacuum leak.. or the base of the tbi is leaking.. Well I did the ole trick of spraying carb cleaner on the base of the tbi, on all the vacuum hoses leading to the tbi.. no change in idle. Next though was.. the IAC is stuck open or something along them lines.. which is where I think my problem lies<< I also checked my base timing just for ***** n giggles and it is spot on. The truck had low idle before.. in park or in gear it ranged from 500-700 the whole time I would say. After rebuilding.. at idle it is about 1100rpms and in gear around 800 I would say. So I guess what I might be asking is what is a normal idle range on these trucks? was my tbi that stopped up that it was causing a low idle and it is at a normal idle now? You ask well why did I rebuild the tbi?? well it was due to a flat spot in the throttle when it is cold. The truck has no flat spot now or anything.. ran decent before and still runs great now.. just feel like there may be an issue with the idle? is my idle range now normal or is it a little excessive?

 

[ChrisAU]

That is high. Did you do an IAC re-learn?

 

[2003Xtreme]

No... lol I have never had any of them do that.. first time if that is my problem. lol I disconnected the battery to reset the computer and it didnt change anything.

 

[ChrisAU]

Take a paper clip, make it straight, then bend it in half. Jump the two terminals on the OBD1 connector below your dash all the way at the top right together with the paper clip, and leave it in. Turn the key forward and wait. If you got the pins right, your service engine soon light should flash once, then pause, then flash twice, and repeat that cycle. They say to leave the key turned for 30 seconds, but I don't believe that. What the computer is doing is cycling the IAC back over and over so the computer now believes it is all the way at the farthest back position, it is a dumb system in that the computer doesn't know how far the pintle is extended, it just moves it back and forth from an assumed position.

After 20-30 seconds turn the key off, then pull the paper clip out. Then put your key back in and crank the truck. The ECM should crank with the understanding that your IAC is in the full recessed position, and the IAC should be unless it is very gummed up. When doing procedure you can actually hear and feel the pintle moving back if you touch the IAC valve body.

Hope this works!

 

[DRAGGIN95]

Take a paper clip, make it straight, then bend it in half. Jump the two terminals on the OBD1 connector below your dash all the way at the top right together with the paper clip, and leave it in. Turn the key forward and wait. If you got the pins right, your service engine soon light should flash once, then pause, then flash twice, and repeat that cycle. They say to leave the key turned for 30 seconds, but I don't believe that. What the computer is doing is cycling the IAC back over and over so the computer now believes it is all the way at the farthest back position, it is a dumb system in that the computer doesn't know how far the pintle is extended, it just moves it back and forth from an assumed position.

After 20-30 seconds turn the key off, then pull the paper clip out. Then put your key back in and crank the truck. The ECM should crank with the understanding that your IAC is in the full recessed position, and the IAC should be unless it is very gummed up. When doing procedure you can actually hear and feel the pintle moving back if you touch the IAC valve body.

Hope this works!

Word, it defintily sound's like a IAC issue, I have even had to swap IAC's because of this issue.

 

[ChrisAU]

Word, it defintily sound's like a IAC issue, I have even had to swap IAC's because of this issue.

Yeah I think thats actually where I'm going next if my rebuild didn't fix my issues...my IAC is the only sensor on my entire truck that isn't Delphi, and only one is AC Delco, which is my CTS which is my other suspect...

 

[2003Xtreme]

I didnt realize it was that easy! Lucky I have one of those key deals to put in those first two prongs to read out my codes. very good info. I figured disconnecting the battery would rest the cpu. If this fails I will switch it out for a different IAC I have laying around. I will definitly try that! Thank you!

 

[2003Xtreme]

So once you put the clip back out and start the truck back up.. the pintle will begin to move outward to seat in the tbi correct?

 

[ChrisAU]

It will do what the computer tells it to, and the computer believes it is fully back, and the only reason it wouldn't be after that procedure is if it is badly gummed up.

 

[ChrisAU]

Basically lets say the pintle has 5 positions. Lets say you cut your truck off with the pintle in the 3 position, so ECM believes it is in the 3 position when the truck starts. Even after a computer reset, that goes back to factory settings, and who knows what that is. So, if you do the re-learn procedure, the ECM now believes it is in the 1 position and the IAC should be in the 1 position. Without it, it is very easy to move the pintle when you have the TB apart for a rebuild, lets say it moved to position 4. ECM only knows it needs to move it to a certain position based on what is happening in the engine, but it thinks it is in a different position than it is, so it moves it too far or too little or not all when it should be moved.

Big downfall of the TB engines, lots of dumb sensors that don't talk back to the computer, only one way communication. The TPS is actually like that too, but harder to mess up as most people put them on with the least resistance when it will actually go on the other way and someone may not know any different.