erratic idle and surging at low speed
03-01-2009, 08:56 PM
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erratic idle and surging at low speed Hey everyone
i installed a ls6 intake manifold two days ago. Well everything went according to plan...broke my oil pressure sending unit and swore more then a sailor. Well When i started my car up (98 trans am, no internals mods) I noticed erratic idle..the car would idle real low..the 500rpm range. The car never has stalled but gets close. When i let it warm up it will flucuate between 500 all the way up to 2k..however when its in park it ranges from 1k-2k..in gear drops to 500.
I unplugged my maf and the idle stopped searching so much and sounded good at a little under 1k...but then in neutral it was up to 1500..I read here that the IAC could be dirty. It was filthy but after i cleaned it and did a pcm relearn it still searches a lot..with terrible lag in low end throttle response and low end driveability and bad idle quality
...any suggestions will be greatly appreciated
i installed a ls6 intake manifold two days ago. Well everything went according to plan...broke my oil pressure sending unit and swore more then a sailor. Well When i started my car up (98 trans am, no internals mods) I noticed erratic idle..the car would idle real low..the 500rpm range. The car never has stalled but gets close. When i let it warm up it will flucuate between 500 all the way up to 2k..however when its in park it ranges from 1k-2k..in gear drops to 500.
I unplugged my maf and the idle stopped searching so much and sounded good at a little under 1k...but then in neutral it was up to 1500..I read here that the IAC could be dirty. It was filthy but after i cleaned it and did a pcm relearn it still searches a lot..with terrible lag in low end throttle response and low end driveability and bad idle quality
...any suggestions will be greatly appreciated 
03-01-2009, 09:17 PM
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I had a similar problem at the track last year. First rule out any vacuum leaks around the manifold. My IAC was constantly searching after a burnout. If you cleaned the IAC and reseated it, you can also check the TPS, your TB. They all have to work together to send the correct signals. What are you using for a TB?
03-01-2009, 09:28 PM
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stock tb from a 98..stock all the way down to no coolant bypass.....how do i test for a vaccum leak? i disabled my air system..by pulling out the fuses out..so those wouldn't cause a leak would they? also my OPSU broke but that wouldn't cause a problem would it ? how do you check the tps?
03-02-2009, 03:26 AM
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Sounds like a vacuum leak to me too. Use dome lighter fluid, carb cleaner, etc. around the manifold, make sure the vacuum lines are all connected correctly, etc. How did you accomodate the coolant lines under the manifold?
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03-02-2009, 09:55 AM
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ok so i sprayed some maf cleaner around the intake..when i got to the back ..the rpms jumped 1k..i tried this serveral times..so i tugged on the brake booster hose and with a little pulling pressure i could hear a whistle..so i am 99% sure vacuum leak..when i removed that hose from my ls1 intake..it would not budge..so i had to take a flat head screw driver and pry it off...so i wonder if i stretched out the opening too much...also is there a clamp on the intake manifold side of the brake booster ??
03-03-2009, 09:17 PM
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ok it's a vacuum leak and its coming from the protruding fitting on the back..where the hvac and brake booster go into...its gasket is showing ..so my question is how do i remove it/put it back on all the way.. :S
