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Throttle Body to vacuum line connector '99 Grand Prix (Also, erratic idle issue)

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killswitch83

New member
Hello everyone, I'm new here and kinda stumbled across this forum, glad to have found it too :). I have been having erratic idle issues with my '99 Grand Prix 3800 non-supercharged engine (ie will surge to 3000+ then drop hard to around 500 RPM). I pop the hood and find the vacuum connector that comes from the side of the throttle body and joins together 2 hard vacuum lines is completely split up the middle. First, what is this thing called, and second, where can I get it? I've looked on Advance Auto's site and couldn't seem to find it. I'm also thinking the IAC is beginning to cause problems too, as the erratic idle begins a short time after cranking up (2-3 minutes) though it will run fine on the road and after you first crank it up (I plan on replacing the IAC as well). Also guessing I'll need to pop off the air cleaner assy and clean out the TB while I'm at it too from what I'm seeing here......Thanks in advance everyone!
 


Awesome, yep that's what I'm definitely looking for, and I see sites that have it as low as a couple bucks, so time to order I suppose. Much better than paying $35 for it at the dealership
 
Well, I just got the connector in today, and it is a different style from the 2 to 1 reducer that was originally on it. Guess it's time for a little "engineering" to get it to work (fingers crossed lol)
 


I had a similar problem with that connector being split but the idle on my car wasn't surging up and down I just took another connector like it from a junk car in the local junk yard (got their permission first) now...no more split connector.
 
Yeah I'm kinda thinking the next step's going to be cleaning out the TB and replacing the IAC considering how it's running and all
 
Anyway, so I got the vacuum connector to work, solved the vacuum leak I had, however I still have the erratic idle issue. I've already checked the TB, air box and all appears to be clean (air filter still looks clean as a pin as well). My first thought was that the IAC was done, but then I remembered I got a CEL sometime ago for Bank 1 O2 sensor that I never did resolve (which I'm hoping it's just the sensor and not a clogged cat). Would a fouled O2 sensor cause this issue, or what would do you guys think?
 
U cleaned the tb? It's possible that if u took it off, the gasket could be cracked, and just need a good changing. Or maybe check all the other evap lines for crack. The tps is also another thing I would check
 


Had to do an engine swap at 184K due to a borked oil pump, this engine currently has about 150K on it, car itself has about 242K........I suppose I didn't get a good enough look into the TB though the screen looked only a little bit dirty, is it a pain to take off? Kinda new at this stuff but I have basic tools.
 
tb isnt bad, just a few bolts. watch though, a little coolant will come out when it comes off. 150k is right around the time for the cats to go bad, tho u most likely didnt change the cat when you did the engine, so it is probably pretty old. but i dont know if that would cause surging. front o2 can cause this i think. also, try running the car with your maf sensor unplugged and see if theres a difference.
 
I will unplug the MAF next time I start her up to see if that's it, elsewise I'm going to replace the O2 sensor to see if that helps. I wonder something though: would gutting the cat adversely affect performance if it is indeed a bat cat? I know some cars require that pressure from the cat to run properly. Also, when you say relearn, do you mean a simple reset via disconnecting the battery, or are we talking a flash? Thankfully this isn't my DD just something I'm trying to get together for a friend to drive (apparently he doesn't like his gas-guzzler of a pick-up lol)
 
Yea, just keep the battery unhooked overnight. I could be wrong, but I think the vacuum leak could have affected the tps, so maybe a relearn could fix it. Don't quote me on that though lol. And I don't think gutting the cat would cause negative effects, except u wouldn't pass inspection. But based on ur symptoms, I doubt that it's the cat.
 


Oh ok, I'll definitely disconnect the battery then, although the car's been sitting for a bit and the battery's now junk (was going when I parked it 4 months ago, been jumping it to crank her up each time). Therefore, will give the TB a good cleaning, change the O2 sensor, and swap out the IAC if necessary. This is a good start and is much appreciated :)
 
How about resurrecting a dead thread eh lol........Welp, I got a suggestion at work for what might be my problem, which was the MAF sensor. I noticed something was amiss when the engine ran the same without it being connected as it does when it is, so I got some MAF cleaner and pulled my MAF sensor. Needless to say, the elements on the inside of it were tarnished a bit, and overall the sensor looked like it needed cleaning, so I did. When I reinstalled it and cranked her up, at first she had a little bit of an erratic idle, but then as the engine was getting to operating temp, it started and kept running fine, albeit rich (which of course I need to replace/clean the O2 sensors). We'll see if she keeps running well, as my GT isn't my daily driver anymore and I'll have time to diagnose and repair as necessary. Thanks for all the input guys!
 
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