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Discussion Starter #1
First of all, I am new to this forum. Thank you in advance to anyone who offers their opinion!

I have been having issues with the idle on this car. Start the car, idles fine for about 5 seconds, then jumps to around 2000-2200 rpm, then sorta moves up and down from there back down to 1000 rpm. Also seems to hesitate and sorta sputter when it's given any sort of gas. Mass air flow sensor already replaced...

My only thought, mainly from reading all sorts of stuff on the web, is either the Cat itself, or the O2 sensor. Any ideas? I already have a stock down pipe/cat off my old 2001 Grand Prix with the same 3800 motor that I may try to swap out. According to any diagrams I have seen, they are the exact same part... Anyone have any info on that as well???

Again, thank you for any advise!
 

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Any vacuum leaks? Also I know on other cars there is an idle air control valve that can sometimes act up in the manner you are referring to.

BTW, any trouble codes, in other words is the check engine light on or been on recently?
 

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Discussion Starter #3
Any vacuum leaks? Also I know on other cars there is an idle air control valve that can sometimes act up in the manner you are referring to.

BTW, any trouble codes, in other words is the check engine light on or been on recently?
It doesn't "sound" like there are any vacuum leaks... The engine light was on before replacing the air flow sensor, but not since. I plan to take it to have the codes checked, but I am hesitant because I have to drive it further than I really want to drive it at this point... I may just try to swap out the Cat first and see if it helps. Then if it runs a little better, I will get it somewhere to have the codes checked.
 

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Discussion Starter #4
I let it run for about 15 minutes tonight... I guess it wasn't dropping down as much as I thought it was. It goes up to about 2000 rpm and stays sorta steady between there and about 2200. I'm going to replace the Cat and the upper/front O2 sensor, because the lower/back sensor is only a year old.

Anyway, still really makes me wonder. When it idles high, I can kick the gas and it will drop down to about 1000-1100 rpm, but goes right back up to 2000. Funny thing is that when I kick the gas, it bogs way down, like it can't breathe or something...

Any more opinions??? Thanks!
 

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the cat isn't going to cause a high idle. It sounds like you have a vaccum leak. Spray around the intake with some carb cleaner and see if it sputters. Check the hose after that MAF sensor make sure its tight and not torn or anything. If all seems well... check the MAP sensor located on the top of the intake on the passenger side. Unplug it and see if anything changes.
 

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Discussion Starter #6
the cat isn't going to cause a high idle. It sounds like you have a vaccum leak. Spray around the intake with some carb cleaner and see if it sputters. Check the hose after that MAF sensor make sure its tight and not torn or anything. If all seems well... check the MAP sensor located on the top of the intake on the passenger side. Unplug it and see if anything changes.
Thank you! I will try the things you suggest. Do you have any pics of the 2 sensore you are referring to that I can check? This is my g/f's car so i'm unfarmiliar with it and the sensors... Thank you!
 

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Discussion Starter #8
Thank you! The links don't appear to be working. Does aryone have an actual picture of where the MAP sensor is located??? Or is there a diagram sticker somewhere under the hood???
 

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Thank you! The links don't appear to be working. Does aryone have an actual picture of where the MAP sensor is located??? Or is there a diagram sticker somewhere under the hood???
Sorry about that.. I have fixed the links so if you click on them now they should work. I don't know where the map sensor is exactly but it should be close to the intake manifold, prolly around the driver side.
 

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Discussion Starter #10
I found a vacuum leak and plugged it, now the idle is back to normal. But I took it out for a drive and now the CEL is on... Will post that in a new thread. Thank you guys for your help!
 
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