Excessively high idle after trans Install. ?!?!

[greengrandam84]

I just finished replacing the transmission in my 00' grand am with one from an Alero that had approx 52k miles on it. Got it all back together last night only to hear this awful rattling noise. (IIRC it was idle'n fine last night) Narrowed it down to the tensioner, replaced the drive belt tensioner this afternoon at work. Afterwork i buttoned everything back up and started it up. seemed fine. took it for a drive around town. ran ok, but then i noticed the idle was around 900 while sitting at a stop light, so i put it in park to see what happens and the idle goes up to like 1200 rpm. Kept driving it around town for about 35 min doing the same thing. ONLY ONCE did i come to a stop and the idle went down to normal range but once i rev'd it, it only came back down to around 900. THEN I come home open the hood check everything, all seems good and plugged in. I turn it off for a few min, start it again idles even higher this time around 1500. I rev it a bit then it stays around 2000 rpm, then i get so pissed I go inside get the manual out and see what it says, wasnt much help so Now im asking you all !!! haha.
What do you think is the problem? Could it be anything with the new trans? Oh yea its a 00' GA SE2 3.4L 155k miles. never replaced the fpr or any other sensors under the hood. Except the oil pressure sensor and a Crank position sensor. Thank you for any and all ideas.!!!!

[Sonyman]

You gotta vacuum leak some where. Either a line or a intake manifold gasket. Check'em both out.

[greengrandam84]

Im gonna start with the idle air control valve. if that doesnt fix it then I'll know its a much larger issue. I hope its nothing serious though. That trans and steering rack and other parts, made me broke..

[greengrandam84]

UPDATE:: its about 1:12pm around 65 deg here, i just went outside to move my car for a co worker and now the engine seems to be idling just fine, around 775-850ish i guess, i didnt let it warm up and see what happened, but now im confused as to why it's acting like this.

[3400-95-Modified]

Did you have the ECM unplugged for a while when you were doing the trans swap? Or just the battery unplugged? And how long has the car been run for idle durations since the trans install... such as have you let it sit there for a while and just idle, or have you driven it on a 30-45 min ride?

[greengrandam84]

I've let the car Idle quite a bit after the trans install. Prob a good 4-6 times for like 15-25 min each time. Yes the Battery was out of the car for about 1.5-2 wks.

UPDATE::: last night they guys and I took a look at the car while at work. It was idling fine when i brought it in. only thing we saw is that i forgot to tighten the intake duct clamp, so i tightened it and went out and drove it around town. i get home about 25 min later out it in park and the rpms jump up again, so there in my driveway i installed the idle air control valve. Started the car again ran fine. went inside took a break for about an hr or so. Then went and drove around town for 20 min before going to the gym, the whole time the idle was fine. THEN when i leave the gym, i start the car and its idling at like 1500 rpms again. SO it's obviously not the IACV. Now im super confused as to what it might be. OH and still no codes.

[3400-95-Modified]

do you have a scan tool to connect to it and see if you can read the MAP value at idle? that reading should help you find a vac leak if there is one.

[CobraCDR]

Sounds like a vac leak to me as well either that or you have a sticky throttle blade? If you tap the gas does it return to normal idle? What is the condition of your TPS?

[greengrandam84]

Im going to try one of the scan tools here at work, not sure if it'll work or not seeing as how its a Hyundai scan tool. What should the MAP reading be for normal?
As for the sticky throttle, no if i tap the gas it changes nothing, goes right back to where it was idling. im going to clean the TB and the mass air flow meter today though, see what happens. Keep yall posted.... Thanks for the help/ideas.

[CobraCDR]

use a spray bottle of water and start spraying the vacuumn lines, if you hear the idle change you found your vac leak

Ken

[greengrandam84]

Well im not sure what exactly the problem was but it seemed to fix itself i guess. I replaced the IAT sensor anyway since I had bought it. Last it happened was in the morning on the way to work on thursday. But by lunch time when I started it, it was fine. Brought it into the shop after work, checked for Vac leaks, didnt find anything. replaced the IAT sensor, unplugged the battery for about 15 min. Hooked it all back up and its been fine ever since, *KNOCK ON WOOD*.