Idle and Running Problem
Thread Starter
Staging Lane
Joined: Jan 2007
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Idle and Running Problem I swapped a 1999 LS1 from a Vette into a 1981 Trans Am. I bought a customized factory harness from a 2000 Z28 off of EBay. I had the engine running fairly normal, but it turns out that the power brake booster was leaking the whole time. I replaced the booster (fixed the vacuum leak), and now the car runs terrible. It wouldn't stay running unless I pulled the vacuum line from the booster and reintroduced the leak. I looked at the wire diagram for the IAC motor and saw that the 2 green wires were switched in my harness. I figured that the guy who customized it maybe screwed up. So, I switched the 2 green wires back to where they should be according to the factory wire diagram and now the car idles at about 2500 rpm and smells really rich. I replaced the IAC motor with a new one, just to make sure that my old one was good and it was. The car reacted the same way with both IACs.
Does anyone know what might be going on? The car is running terrible and I cannot control the idle.
Does anyone know what might be going on? The car is running terrible and I cannot control the idle.
Are you getting a check engine light?? What exactly was "customized" on the harness you bought? Have you tried to pull power to the pcm for a few hours and let it idle relearn?
If you are getting a check engine light, that can help. If you arent, and you tried to reset the PCM to no avail, I would say something in the wiring is causing an issue. Im just wondering if the motor learned to cope with the vac leak and now that you took it away it is all screwy. I could be totally off base tho... Im sure someone else will chime in with some ideas.
Justin
If you are getting a check engine light, that can help. If you arent, and you tried to reset the PCM to no avail, I would say something in the wiring is causing an issue. Im just wondering if the motor learned to cope with the vac leak and now that you took it away it is all screwy. I could be totally off base tho... Im sure someone else will chime in with some ideas.
Justin
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 59
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The customization to the harness was basically the deletion of all emissions equipment and anything else not needed to run the engine in my car. It also was made to only use 2 oxygen sensors, not 4. I have another PCM that I'm going to try. It just feels like something is very wrong though. I'm also worried that the 2 wires I switched to the IAC were in the right place to begin with and that the wiring diagram in the service manual is wrong. I'll try to find a diagram from another publication to compare it with.
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 59
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Originally Posted by ghettocruiser
Are you getting a check engine light?? What exactly was "customized" on the harness you bought? Have you tried to pull power to the pcm for a few hours and let it idle relearn?
If you are getting a check engine light, that can help. If you arent, and you tried to reset the PCM to no avail, I would say something in the wiring is causing an issue. Im just wondering if the motor learned to cope with the vac leak and now that you took it away it is all screwy. I could be totally off base tho... Im sure someone else will chime in with some ideas.
Justin
If you are getting a check engine light, that can help. If you arent, and you tried to reset the PCM to no avail, I would say something in the wiring is causing an issue. Im just wondering if the motor learned to cope with the vac leak and now that you took it away it is all screwy. I could be totally off base tho... Im sure someone else will chime in with some ideas.
Justin
Originally Posted by 451stroker
By the way, I don't know if I'm getting the check engine light because I don't have it hooked up yet.
Knowing what codes you are throwing, if any, will really help you to diagnose your problem.
As for the switched wires, chances are if all the person who made it did was delete wires for emissions and rear o2 sensors, then the wires were in the right place to begin with. Usually when you do that, you just pull wires from the PCM connectors, but you leave the rest of the harness alone and in its factory configuration.
If you are still confused and curious about the wires, just trace them from the PCM connectors. Make sure the wires are in the correct spots on the PCM connectors...if they are, then they should be correct. Because I doubt the person switched the wires at the plug...atleast they had no reason to.
Let us know if you figure things out or if you need some more help!!
Justin
Thread Starter
Staging Lane
Joined: Jan 2007
Posts: 59
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I switched the IAC wires back to their original positions. The 2500rpm idle is gone, but the car is back to not really idling. I have to feather the gas to keep it running. I also checked the codes with my OTC scanner and there are none. I even tried my other PCM and there was no difference. Could this be a tuning issue at this point?
You are using a vette motor...and an IAC so I assume you are using a cable throttle body??
If so, is it a stock or aftermarket throttle body? Couple things I would try as long as its a cable TB. Ide try resetting the PCM by pullin the fuse for a few hours. They usually will idle funny at first after this, but will eventually learn the idle.
If it still isnt idling high enough, you can use the set screw on the throttle lever to bump the idle up. I think you have to reset the TPS after that though. There is a procedure around here somewhere for doing that as well.
Other than that, I would say its a tuning issue. Sounds like your IAC wires are correct now. Since you arent getting any codes, I would check the small things and then worry about it being a tune issue.
Justin
If so, is it a stock or aftermarket throttle body? Couple things I would try as long as its a cable TB. Ide try resetting the PCM by pullin the fuse for a few hours. They usually will idle funny at first after this, but will eventually learn the idle.
If it still isnt idling high enough, you can use the set screw on the throttle lever to bump the idle up. I think you have to reset the TPS after that though. There is a procedure around here somewhere for doing that as well.
Other than that, I would say its a tuning issue. Sounds like your IAC wires are correct now. Since you arent getting any codes, I would check the small things and then worry about it being a tune issue.
Justin
