Time to dynamite my LT-1
Thread Starter
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Time to dynamite my LT-1
I've been fighting a high idle problem on my 93 LT-1 6 spd. engine idles at 1000 rpm, 750 to 800 with A/C on. I'm at a loss to find the cause. Doing minimum idle adjustment I can back screw away from throttle blade and idle wont drop below 500. I think its a a vacuum leak but where????
Things I've done.
Cleaned throttle body and IAC enclosure, new gaskets.
No leaks at throttle body shaft
New IAC
New TPS
Removed (2) vacuum lines from intake and capped fittings for test, no change
Removed and capped evap control line from solenoid, no change
Replaced PVC valve and lines
Sprayed intake with starter spray to look for leaks, can't find any.
WHAT ELSE IS LEFT??
Wild a*s guesses.
Intake manifold leak, even though spray doesn't show it. No water or oil leaks.
A/C request signal to ECM even though A/C is off
Sponge TPS gasket leaking, even though spray doesn't show it
Either I find an answer or I get out the dynamite
HELP.
Larry
Things I've done.
Cleaned throttle body and IAC enclosure, new gaskets.
No leaks at throttle body shaft
New IAC
New TPS
Removed (2) vacuum lines from intake and capped fittings for test, no change
Removed and capped evap control line from solenoid, no change
Replaced PVC valve and lines
Sprayed intake with starter spray to look for leaks, can't find any.
WHAT ELSE IS LEFT??
Wild a*s guesses.
Intake manifold leak, even though spray doesn't show it. No water or oil leaks.
A/C request signal to ECM even though A/C is off
Sponge TPS gasket leaking, even though spray doesn't show it
Either I find an answer or I get out the dynamite
HELP.
Larry
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Sure sounds like the IAC is going bad. Some times you can clean them and make them work. Other times you just have to replace them because they just don’t take the commands from the ECM correctly. When I have those problems I just like to change them and be done with a high failure rate item. 
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Originally Posted by Red Dwarf
Isn't there a procedure for the TPS re-learn (idle speed) when this component & the throttle body are replaced?
Thread Starter
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Thanks for suggestions so far.
IAC is new. Problem exists when doing minimum air adjustment with IAC disconnected from ECM.
IAC was set at 28mm per spec before install
TPS is new but problem existed before I changed it. TPS is not adjustable on LT-1. I did not reset with an Tech-1. I don't recall seeing that in manual.
I did not check EGR vacuum. I would expect to see trouble code if EGR was sticking. Am I wrong? Idle is not rough which is what I would expect with a stuck EGR. Its smooth but high.
Thanks for help. Keep ideas coming.
Larry
IAC is new. Problem exists when doing minimum air adjustment with IAC disconnected from ECM.
IAC was set at 28mm per spec before install
TPS is new but problem existed before I changed it. TPS is not adjustable on LT-1. I did not reset with an Tech-1. I don't recall seeing that in manual.
I did not check EGR vacuum. I would expect to see trouble code if EGR was sticking. Am I wrong? Idle is not rough which is what I would expect with a stuck EGR. Its smooth but high.
Thanks for help. Keep ideas coming.
Larry
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Thread Starter
Pro
Joined: Apr 2005
Posts: 590
Likes: 0
From: Boynton Beach, FL
Originally Posted by Red Dwarf
Just a suggestion, but see if you have a code stored for DTC 21 or 22?
Larry