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Engine idling at >2500 only when hot???

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Old Feb 23, 2010 | 09:18 PM
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Default Engine idling at >2500 only when hot???

My wife`s `98 Trans am is trying to keep itself at 2500 rpms or above, but only when the engine is hot, atleast above 180º. When the engine is cold, it runs perfectly. There is no loss of power, in fact, in runs quite strong. When it starts acting up, I can completely let off the gas in 4th gear and it will maintain speed indefinitely. Slamming down on the gas has no effect, except what you would expect when you slam down on the gas. The engine still drops back down to 2500 rpms or so. Once we let the engine cool down, it runs fine again. It just started doing this. It also seems as though the charge voltage is down, just under 13 volts, when it happens. It also sounds as though the electric fan motors are struggling, which makes me think it is related to that.
Any ideas?
Thanks!
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Old Feb 23, 2010 | 09:25 PM
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Have you recently done any mods? Sounds like it could be tuning related? Maybe your base running airflow table set way to high in the upper engine temps? It just started happening out of the blue, without any changes being made to the car? Hard to know with given information. Not trying to be a DH just need more information.
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Old Feb 23, 2010 | 09:28 PM
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Originally Posted by LeftySS
Have you recently done any mods? Sounds like it could be tuning related? Maybe your base running airflow table set way to high in the upper engine temps? Hard to know with given information.
Yeah, in fact she just had the engine replaced. However, it was a stock LS1 block with the only changes being an LS6 cam and springs. Other than that, stock from the airbox to the tailpipe.
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Old Feb 23, 2010 | 09:32 PM
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So did it drive fine once she got the car back? Or has it done this ever since the engine was replaced?
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Old Feb 23, 2010 | 09:41 PM
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Originally Posted by LeftySS
So did it drive fine once she got the car back? Or has it done this ever since the engine was replaced?
Yeah, the car seems to have been driving great until this. We`ve only had it back since Saturday though. But she has been driving it alot, as she is really excited to have it back.
About the DH thing, no worries. I just appreciate the help.
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Old Feb 23, 2010 | 10:26 PM
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Hum. Who changed the motor out? Did they do anything to the tune being that there is a different cam. I would think a stock tune on that cam wouldn't do that, but I am not sure. Have you checked all the vaccum lines? I am not sure if the AIR or EGR system could cause something like this or not? Sounds to me like it is something in the tune, a leak somewhere that gets more pronounced as the car heats up, or maybe the IAC is on the fritz. I am racking my brain trying to think. Maybe someone else that has had this happen will chime in. I will keep thinking but kinda at a lost. Sorry.
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Old Feb 24, 2010 | 06:14 AM
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Could it possibly be the electric fans shorting out and draining the voltage, and the computer is trying to compensate and keep it running by raising the rpms?
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Old Feb 24, 2010 | 07:57 AM
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Also forgot to mention.....it is hard to start the car just before this happens, sorta like the battery is just about dead. If I have a hard time starting the car, I know it is going to act up, and it does start acting up immediately.
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Old Feb 24, 2010 | 08:00 AM
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Yeah possibly. Could be your alternator. Was it replaced with the engine? That would be the cause of the battery feeling like it is almost dead.
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Old Feb 24, 2010 | 10:36 AM
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I would pull the battery and take it somewhere to have it checked.

I was just reading another post last week I think where these cars do wierd **** when the battery is taking a ****.
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Old Feb 24, 2010 | 10:41 AM
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def sounds like a battery / alt issue. did the old engine overheat and die? if fans were bad they would blow fuse
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