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Please Help!!! GTP surging idle

Damon318

Damon318

New member
Hey everyone, i'm new to this forum but i've read great stuff from all you guys i hope you can help.
First of all i have a 98% stock 98 GTP with 185k i've replaced the crankshaft sensor, MAF,Plugs and wires, K&N air filter, Thermostat, Battery and all the fluids (except the super charger oil, going to do soon).
on start up things go great. It fires up right off and the tach goes up to about 1100 rmps but then it starts to drop very slowly until it reaches about 500-700 rpms then it just sits there ROUGHLY idling. The needle on the tach barely moves up or down but hardly noticeable just bouncing from 600-800 rpms but its almost like the car is shaking slightly. i've been running low octane fuel for about six months but recently switched back to 91 (after reading this forum!).
All symptoms are GONE above 1100 rpms and everything runs great except for my idle, it's awful. i cleaned the sensors on the TB with TB cleaner and replaced the MAF and i don't know where to go next!?
ps. no codes at all cleared them after replacing the MAF and nothing so far.
 
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Idle misfires are not uncommon on these cars when theres no load on the engine (in park or neutral). If its bouncing from 600-800 rapidly though Id be looking for a possible vac leak
 
thats what i was leaning towards, how do i check for vac leaks? and have you ever used seafoam? i hear it works wonders?
 
Check all of your vacuum hoses and connections. Could be a that something disconnected/dry rotted/pinched/cracked, etc.
 
My 06 malibu and 05 GTP both display the same idle issues as what you describe. Both cars a very well kept and have properly gapped plugs and new wires, they still have a slightly stumbling idle. I think it's just that these cars and other GM V6's are prone to an idle misfire condition like mentioned earlier.
 


dang not what i wanted to hear :( i did a seafoam tonight and changed the fuel filter cleaned the plugs and it worked great car runs amazing! just idles like sh**!!!! im thinking about taking it to the dealer to get it tested but its like $75 just for a diagnostic!!!
 
no luck for the vacuum leaks but i found a cracked tube on my SC! i replaced it tonight now my boost feels amazing. but no luck on the idle. i hear a hiss but i looked for hours with no luck. any good methods of searching? besides like a smoke machine (way expensive!)
 
Damon318 said:
no luck for the vacuum leaks but i found a cracked tube on my SC! i replaced it tonight now my boost feels amazing. but no luck on the idle. i hear a hiss but i looked for hours with no luck. any good methods of searching? besides like a smoke machine (way expensive!)
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Water bottle with a high soap/water mix. spray it around the lower intake/throttle body/Sc/Injectors and see if you hear it get sucked in or see it bubble
 


Alright i feel realy stupid asking this but i sprayed the carb cleaner and my idle went right back to normal so i figured im on the right track it a vacuum leak! i thought this was great news until i traced it down to a machined whole on the engine side of the TB( WTF!?) Im no motor head and have no idea what this whole is? its sucking in air and when i spray it with the carb cleaner my rpms go right to normal? i dont know what this means but i dont think its a vacuum hose leak? maybe check the other sensor on my TB?
 
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alright im at a total loss! i replaced my plugs wires maf iac fuel filter oil and filter did a sea foam clean checked for vac leaks tore apart my TB and cleaned it from top to bottom cleaned all the new sensors let my car run with out the maf (still a problem so its not the new maf) put in new gas and injector cleaner checked my throttle positioning and i still have a horrible idle below 1000 rpms! and now when im driving at highway speeds and let off the throttle my rpms drop to 1000 and then bounce back up to around 2.5!? any help at all would be greatly appreciated.
 
Oh my, test, don't guess man. Did you ever fix the hole that you mentioned in your previous post? Why don't you post a pic of the hole that you are talking about. Most of us work better when we can see what you are talking about.
 
Take a pic of that hole and show it to us. There should be no hole in your TB that you can spray and have it change idle. There's only one vaccum port on the TB and it should be going to the evap.
 
ill go take a pic right now its a machined hole i thought it was to the iac or something but like i said im just learning i really appreciate the help guys!
its on the sc side not the TB my mistake
 


this is the whole and if i spray it my car idles perfect. its on the supercharger side but i looked and it connects to the TB i thought it was something to do with the iac for adding extra air if there was a problem but thats a shot in the dark?
any ideas?
mail
 
My phone is not bringing up a pic, and my work computer's firewall is blocking the image hosting site as well. I can't help you out with the picture man, sorry :(

You are changing too many variables at once. Test one thing at a time. You should put your old sensors back on and make sure the tps that you messed with is set back to the same position that it was in before you messed with it.
 
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