strange idle problem

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Sep 1, 2002 | 07:22 PM

2manyFbods

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From: Arizona

strange idle problem

A Friend of mines 98 SS M6 started having a problem after the Cam/intake were installed. With the engine cold it will idle at 900. After letting it warm up to temp, the idle will climb to ~ 2100 RPM for 20 to 30 seconds then goes to about 900. Then it keeps repeating this cycle up and down. Power falls off at ~4000. It hits the rev limiter at ~6200 even though the limiter is set for 6600??

- PCM has been tuned by 2 different vendors.
- TB, TB sensors and MAF have been swapped.
- O2's 990mv+ WOT
- Codes po171.po174, p1336

Problem still exsists. He has LS1 Edit now to make any changes. Mods are: TR224, LS6 intake, longtubes, ported TB and SLP MAF

Any help would be greatly appreciated.

Larry

Sep 2, 2002 | 01:00 AM

NoGo

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From: Mass

Re: strange idle problem

Vacuum leaks will raise your idle and make the car slow to returning to idle. If large enough, they can cause surging. I don't know about surging to 2100 rpm for 20 seconds!

Anyhoo, if it started after your intake install it should be something to check for. Get some carburator cleaner (or starter fluid, basically some highly volotile ****) and spray it around the intake. If the idle goes up, you know you have a vacuum leak.

Make sure you do this when the car is STONE COLD. There's nothing like the fireball that errupts after starter fluid hits a hot exhaust <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Good Luck
<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Sep 3, 2002 | 08:13 PM

NastyWS6

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From: SoCal

Re: strange idle problem

Definitely sounds like it is a vacuum leak.

Sep 3, 2002 | 09:48 PM

wrencher

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From: Chicagoland

Re: strange idle problem

Try this method to look for a vacuum leak, propane bottle torch tip removed 2 foot 1/4 inch vacuum hose on end of bottle, turn on & check works great & no fires hot & cold engines. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Sep 4, 2002 | 01:15 PM

2manyFbods

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From: Arizona

Re: strange idle problem

We have tried looking for leaks around the manifold. Richard came to my house one day when it was idling high, we swapped the TB and MAF from my car to his and the problem went away.(we only left my parts on for a few miles) He has since bought a TR Ported TB and already had a SLP MAF that had not been installed yet. The problem still exsists with the new parts. Any further ideas?

We have also found the "Bad VSS" rev limiter set for 6200 in the program which my explain why the car hits the Rev Limiter at 6200 instead of 6600.

Sep 5, 2002 | 09:32 PM

2manyFbods

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From: Arizona

Re: strange idle problem

Well........We went back to square one...... and found a vacuum leak. <img border="0" title="" alt="[Embarrassed]" src="gr_emb.gif" />

Larry

Sep 6, 2002 | 02:36 AM

slick98ta

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From: O'Fallon-MO.

Re: strange idle problem

Where was your vacum leak at? I put on a LS6 intake and going through the same thing right now and getting the same codes as you are.And my idle surges bad for 900rpm's to about 1500rpm's

Thanks
Mark