Hey fellas,
My 98 gt has been talking back to me lately. Its got 115,000 miles on the motor. Problem is a high idle and a slow return to idle. Ill typically idle anywhere from 1300 to 2000rpm. If i rev hard or accelerate hard the rpms take forever to return to "high" idle. Ive replaced the IAC and EGR thinking that would alleviate the problem because it worked last time. I have not upgraded/replace any fuel system components, no chips or intake either. Any ideas at where to trouble shoot next? Some have said it is the computer??
Thanks
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1998 GT black
Flowmasters on Pypes Off-Road X-pipe
Steeda Double Hook Clutch Quadrant, Firewall Adjuster and Adjustable Cable, King Cobra Clutch
Eibach Pro-kit, Mach 1 tokicos
Steeda Tri-Ax Shifter, BBK UCA's & LCA's, All polyurethane bushings and isolaters
"I don't know which is louder...my exhaust or my stereo..."
Before jumping to expensive conclusions, check the rest of the basics. Idle set screw on the throttle body could have rotated a bit, it doesn't take much. You could also try resetting the ECU by disconnecting the battery. Also check it for any codes, while a check engine light hasn't appeared there still may be some codes.
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Sometimes I think that government fits that old-fashioned definition of a baby: An alimentary canal with an appetite at one end and no sense of responsibility at the other.
- Ronald Reagan
and possible the TPS, if its out of adjustment the computer might kick the idle up. also sounds like could be a vacuum line. a leak has been known to do that.
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2000 GT VERT-- Far from stock, far from where I want it...
AS already stated, check for any vacuum leaks, dried out brittle hoses are the usual bad guys. If you can, use a vacuum guage to get an idea, next would be the TPS, it may not throw a code but still be off. A good parts store can usually scan it for you or you can disconnect the positive terminal overnight and see what happens when you reconnect it, good luck.
Just out of curiosity, how much vacuum should we be seeing at idle? Blue, how much are you seeing with the KB? Sorry bgt98, not trying to hijack or anything!
At idle I still see 23 inches of vacuum. Steady speed with cruise control set I typically stay between12-20 inches, depending on ambient temp, speed and grading.
I agree with the vacuum leak assessment. It's pretty odd that a vacuum leak can cause a high idle instead of stumbling and stalling, but it wouldn't be the first time I've heard of it happening.
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Sometimes I think that government fits that old-fashioned definition of a baby: An alimentary canal with an appetite at one end and no sense of responsibility at the other.
- Ronald Reagan
- check for vacuum leaks (check every line)
- back out the idle screw until the throttle blade starts to stuck in the throttle body, then give the screw half a turn to open up the blade again.
- check the TPS voltage at idle (center pin to ground, ignition on, engine off -> 0.95 - 0.98 Volts)
- Check TPS for flat spots
If that did not do enough, get a 1/2" copper plug with a 7/16" hole in the plug, and put this plug in the idle by-pass hose attached to the intake plennum (right after that small black plastic box).
Important: make sure that the plug can't get sucked into the plennum!
Important: make sure that the plug can't get sucked into the plennum!
That should do it
Yeah, that'd be a really bad day if it happened.
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Sometimes I think that government fits that old-fashioned definition of a baby: An alimentary canal with an appetite at one end and no sense of responsibility at the other.
- Ronald Reagan
well i checked the vaccuum lines and did find one line slightly loose on the intake tube. pushed that in and it seemed to drop the idle by about 100rpm.
checked the TPS voltage and it read .6V. Does that seem low? I haven't gotten it to idle high for about two days, however, it only enjoys doing that when i ride it hard. still searching though....any more ideas?
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1998 GT black
Flowmasters on Pypes Off-Road X-pipe
Steeda Double Hook Clutch Quadrant, Firewall Adjuster and Adjustable Cable, King Cobra Clutch
Eibach Pro-kit, Mach 1 tokicos
Steeda Tri-Ax Shifter, BBK UCA's & LCA's, All polyurethane bushings and isolaters
"I don't know which is louder...my exhaust or my stereo..."
well i checked the vaccuum lines and did find one line slightly loose on the intake tube. pushed that in and it seemed to drop the idle by about 100rpm.
checked the TPS voltage and it read .6V. Does that seem low? I haven't gotten it to idle high for about two days, however, it only enjoys doing that when i ride it hard. still searching though....any more ideas?
.6 is fine at idle... rev the motor, and watch the voltage draw up. It should be a steady rise to 5V and back down as you let off the throttle. If it sticks or stays in 1 spot, it's bad.
Have you tryed cleaning the MAS??? A dirty MAS can cause all sorts off problems. Clean it and disconnect the battery for 15 min. Heres a good website showing you how. http://www.geocities.com/smfoushee/
high idle and i cant figure out why 
