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High RPM's? Idle air control opens?

This is a discussion on High RPM's? Idle air control opens? within the Computer & Tuning forums, part of the LSx Technical Help Section category; Hi everyone! I have a 2000 LS1 in a 33 Ford street rod. And I cannot get it to idle! ...

  1. #1
    Junior Member Shannon2356's Avatar
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    High RPM's? Idle air control opens?

    Hi everyone!
    I have a 2000 LS1 in a 33 Ford street rod. And I cannot get it to idle!
    It has a wiring harness and from Streeet and Performance. And NOW has a computer from them too.

    For some reason the Idle Air Control Vavle opens?

    OK! This is what I have done so far!
    I have had 3 people look at it. 2 came to my shop with scan tools. Both did NOT get any codes that would tell them what was causing it. But we did find out that I didnt have a vacuum leak. Or anything worng with the enigine.

    I can unplug the IACV and remove it. Pull it out by hand reinstall it. And the engine will idle as long as I leave it unpluged. As soon as I plug it back in the computer will open it.

    We took it to a Chevy garage. And they pointed to a bad computer. Since the computer we were using (at that time) was a used on. And also found out that it was out of a 98 Firebird V6.

    So we just spent $500.oo on a new one. From Street and Performance. That would be programed to our engine and transmission.

    Just installed it! And it is still idling high!

    So what do you guys think it could be????????????????

    Hope someone on here can help me out!
    Thanks Shannon Anderson
    Last edited by Shannon2356; 03-29-2009 at 08:05 PM.

  2. #2
    TunedbyFrost.com Tuner Frost's Avatar
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    I'm sorry that you had to go to S&P , I could get you a loaded PCM that was programmed custom for YOUR setup for under $200...

    The IAC is supposed to open and operate in a feedback loop to provide the proper amount of idle airflow for the vehicle.

    The scan tools of those shops are not very helpful, being in front of a tuner with real software would be a lifesaver if he is competent. He would be able to troubleshoot the IAC to ensure it is wired and functioning properly as well as set the base airflow requirements for the TB.

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    Veteran 0rion's Avatar
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    it would be nice to be able to log it and see what the IAC counts are. Just to clarify you have a pcm out of a 2000 f-body now? Are you running the MAF?

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    Junior Member Shannon2356's Avatar
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    Yes I am running a MAF. And I also have to add that the IACV is also new.
    This is what I know.
    Everything is from Street and Performance. But the engine and transmission are both from a GM dealer. The engine is a 2000 LS1 Corvette and the trany is a 4L60E. NOW everything else is for a 98. The IACV is from a Camaro. The computer and wiring harness is also from a 98. So it looks like the only thing that is a 2000 Corvette is the engine.

    OK! What you were saying about the Throttle stop. I have NOT touched it. And it is not hanging open. And I don't think it is out of adjustment. Because I can get the engine up to running temp. Then remove the old IACV. Pull it out by hand. Reinstall it. Leave it unpluged from the harness. And the engine will idle VERY good.

    ?????????????
    What tells the comp. to open the IACV?

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    Veteran 0rion's Avatar
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    frost will have to chime in on this one. The 98's were cable driven and the 2000 vette was a drive by wire. I think that's where your problem is. What throttle body do you have? Cable driven or drive by wire? If it's drive by wire I don't think you need the iac motor because it'll use the throttle body blade.

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    Junior Member Shannon2356's Avatar
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    NO! It does not have ANY of the emisson stuff on it. That is the only codes we were getting when we hooked the scan to it. We also got 2 fan codes and check engine light. Witch we dont have either.

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    If the Vette motor is "fly by wire" wont he need the Vette harness? I would think the 98' Camaro harness would be different at the throttle plenum. Also would'nt he then need the Vette Comp too? Some things not addin' up here. If the comp is tuned for a cable thottle, it would seem to make sense that he could use the Camaro thottle body in place of the fly by wire one. Because there would'nt be plugs there for fly by wire on the 98' Camaro harness. Unless something else is totally different between the two motors and sensors besides the fly by wire setup. I dunno. Just seems something is missing. Probably something simple...

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    Junior Member Shannon2356's Avatar
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    OK! It is a cable. And I think that everything is from a 98. The only thing that is a 2000 is the engine itself. The throttle is from a Camaro. I just replaced the IACV. And the 98 Camaro matched it. So everything electrical is from a 98.

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    Junior Member Shannon2356's Avatar
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    I dont think I can remove it all together. The engine idles very low. And does not ilde at all if its cold. And I also think that the IACV work like a choke when the engine is cold.

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    Veteran 0rion's Avatar
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    Quote Originally Posted by Smittro View Post
    Just A hunch but I bet Without the EGR then you probably no longer need the IACV. If it codes with it unpluged but idles good you maybe able to tune it out and then figure out how to close off the IACV pintle passages.
    the EGR doesn't effect the IAC

    Quote Originally Posted by Shannon2356 View Post
    I dont think I can remove it all together. The engine idles very low. And does not ilde at all if its cold. And I also think that the IACV work like a choke when the engine is cold.
    the IAC works off of a few different tables in the pcm. Here's a screen shot with the IAC tables in the right hand side.


    I'd be tossing guesses to help you with much past just making sure there's no unmetered air getting into the car ie. vac leaks, throttle body set screw backed off, or one thing is since it's from a 98 do you know the history of the throttle body? Perhaps it's been drilled out for a cam or something like that. There should be a hole in the center of the throttle blade but it's popular for people to drill that out larger when doing a cam. You're really going to need to get it in front of a tuner that can log the car and see exactly what the airflow is doing.

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    Junior Member Shannon2356's Avatar
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    The throttle body is stock. And is untouched. Everything on this engine is NEW. And has 0 miles on it. Just run time only.

    Let me ask you guys something alse. Sincfe we are talking about the throttle body.
    There is a water bypass tube. That runs under and through the throttle body.
    Now since I installed this engine in a 33. I had to drill and tap the flat area of the water pump (beside the throttle cable) for a water outlet. NOW instead of running the water throught the throttle bady. I ran a hose behind it and over to the water bypass tube outlet.
    So there is NO water running throught the throttle body.

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    Yeah sorry doing ten things at once,LOL. I totally forgot the function of the IAC.

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    Veteran 0rion's Avatar
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    Quote Originally Posted by Shannon2356 View Post
    The throttle body is stock. And is untouched. Everything on this engine is NEW. And has 0 miles on it. Just run time only.

    Let me ask you guys something alse. Sincfe we are talking about the throttle body.
    There is a water bypass tube. That runs under and through the throttle body.
    Now since I installed this engine in a 33. I had to drill and tap the flat area of the water pump (beside the throttle cable) for a water outlet. NOW instead of running the water throught the throttle bady. I ran a hose behind it and over to the water bypass tube outlet.
    So there is NO water running throught the throttle body.
    that's actually popular for people to do. They bypass the TB to keep the hot coolant out of there. It's only function was to keep the blade from icing up in the winter. Not needed unless it's gets really cold where you're at and you plan on cruising in a 33 ford when it's that cold.
    What intake is on the engine? Does it have the open port for the EGR just behind the TB? If so how did you block that off? You went over all the lines and checked for vac leaks right? If those tables are stock and you have no unmetered air entering the engine I'd probably take a hard look at that throttle body. Like I said before though, I'm guessing at this point.

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    Junior Member Shannon2356's Avatar
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    There is a line comming out of the intake behind the TBS. And goes to a sensor on the pass. side head. It is between the first two injectors. There is a wire pluged into it. And the vacuum is pluged off at that point.
    The reason I dont think its a vacuum leak. Is because it idles to good and smooth. If you pull out the IACV and leave it unpluged. When you unplug it. The engine will run at what looks like 800 rpm's. And sounds great. But when you plug it back in. The rpm's go up.

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    Quote Originally Posted by 0rion View Post
    that's actually popular for people to do. They bypass the TB to keep the hot coolant out of there. It's only function was to keep the blade from icing up in the winter. Not needed unless it's gets really cold where you're at and you plan on cruising in a 33 ford when it's that cold.
    What intake is on the engine? Does it have the open port for the EGR just behind the TB? If so how did you block that off? You went over all the lines and checked for vac leaks right? If those tables are stock and you have no unmetered air entering the engine I'd probably take a hard look at that throttle body. Like I said before though, I'm guessing at this point.
    Agreed on the bypass. As to the other thing I mentioned before, I bet it's something simple we're just not putting our finger on. Startin' to make me crazy and it's not even my 33!LOL

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    Junior Member Shannon2356's Avatar
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    Trust me I know! I wish it had a carb on it. LOL!
    And I have been saying that since the beginning! Its something stupid! Once I find out what it is. I will be kicking myself in the A**!

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    I'm begining to wonder when you bought the new IACV if they gave you the wrong one at this point. Just dont make sense why it's doing what it's doing.

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    Junior Member Shannon2356's Avatar
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    NO! LOL The reason I bought a new one is because the first guy I talked to and had look at it. Told me that it mnaybe sticking. I bought a new one. It is only about 3 weeks old. And the new computor I just installed yesterday. Really thought it would fix it. LOL!

    I want to thank all of you for all the help so far!

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    ʢ ൧ ൨ ൩ ൪ ൫ ൬ ൭ ൮Ր Ց Ւ Փ Smittro's Avatar
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    Quote Originally Posted by Shannon2356 View Post
    NO! LOL The reason I bought a new one is because the first guy I talked to and had look at it. Told me that it mnaybe sticking. I bought a new one. It is only about 3 weeks old. And the new computor I just installed yesterday. Really thought it would fix it. LOL!

    I want to thank all of you for all the help so far!
    No prob, I know what it's like to have a nice set of wheels you cant drive because of something you cant put a finger on. Then you figure it out and feel like hitting yourself in the head with a rubber hammer.LOL

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by Smittro View Post
    Reason I say that is because the comp only knows that the IACV is a "stepper motor" and moves the pintle in and out and cycles between to meter the air flow. It doesnt actually know where the pintle is unless it is fully closed or fully open or hung.....

    This is not true. I don't even log desired position, I log actual...


    Quote Originally Posted by Shannon2356 View Post
    ....
    The reason I dont think its a vacuum leak. Is because it idles to good and smooth. If you pull out the IACV and leave it unpluged. When you unplug it. The engine will run at what looks like 800 rpm's. And sounds great. But when you plug it back in. The rpm's go up.
    If it's a stock motor and you remove the IAC or run it open and the motor idles fine rather than climbing to over 1K, it sounds like the minimum airflow screw on the TB is set too low.

    You know when it's right because the IAC will be at 60-80 counts at hot idle. You need a scan tool to see this. I'd start by looking at TPS with a scan-tool and key-on, and adjust that screw in the TB untilt he blade is open to about 2%. Now turn the key to off, unplug the TPS, turn the key to on and wait a few seconds and turn it back off. Plug the TPS back in and turn the key back to on. Verify with a scan tool that the TPS is reading 0%. Start the motor up and get it as warm as you can; keep the fans forced off. At hot idle you want 60-80 counts on the IAC, and you know that you have it in a proper place in it's operating range.

    Are you sure that your PCM was flashed for a CABLE operated TB? If you told them vette, they may have assumed DBW instead of cable...

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