Quick LT1 idle question
Thread Starter
Racer
Joined: Apr 2005
Posts: 484
Likes: 5
From: Madison Wisconsin
Quick LT1 idle question
I have a 93'. The idle takes a fairly long time to drop down and it never seems to get down to where I'd expect it to be. After the car is warm and I push in the clutch the idle is at about 1,100 RPM. It will slowly drop to about 900 RPM. I tried cleaning the IAC and the throttle body. I also checked for any restriction on the cable. I was able to get it to run a little slower at first, but now it appears the computer adjusted it back to the same spot. Is this normal or is my IAC going bad? I couldn't find anything in my FSM about the stock idle speed.
I really appreciate any tips.
Thanks,
Jim
I really appreciate any tips.
Thanks,
Jim
Instructor
Joined: Aug 2010
Posts: 238
Likes: 0
From: Asheboro North Carolina
I hope someone comes back with a good answer to this as I have exactly the same issue on my '95. I've cleaned the throttle body, checked vacumn and have a consistent 20lbs, replaced questionable vacumn lines, etc. I've cleaned the IAC and MAF sensor, and replaced the O2 sensors. Idle is 100 RPM two high according the the tach. One time just after cleaning the IAC it went down to about 800 but within a short time is was back up to just under 1000.
By the way - ZF transmission.
By the way - ZF transmission.
Thread Starter
Racer
Joined: Apr 2005
Posts: 484
Likes: 5
From: Madison Wisconsin
Thanks for the post. I probably should have mentioned I too have the ZF 6 speed transmission. I'm stumped. I hate to just replace the IAC since it appears to be controlling the idle. I have a few vacuum lines that look a little suspect that I plan to change. Beyond that the only thing I can think of is changing the computer.
Jim
Jim
Team Owner
Joined: Aug 2005
Posts: 34,988
Likes: 515
From: Riverside County Southern California
Co-winner 2020 C4 of the Year - Modified
2018 Corvette of Year Finalist
2017 C4 of Year
2016 C7 of Year Finalist
St. Jude Donor '09 thru '20
I had that issue with The Ghost. I did a IAC reset following the FSM instructions and the problem went away.
If I get the time, I would dig out the FSM and post the instructions here. Try a search, I bet they are already in here.
If I get the time, I would dig out the FSM and post the instructions here. Try a search, I bet they are already in here.
Instructor
Joined: Jul 2011
Posts: 128
Likes: 0
From: Vancouver WA
same problem i had, i even replaced the iac becsaue it was not stepping like it should and i still had the same problem.
I popped off the little metal cover, covering my idel control screw on the throttle body and turned it back. problem solved.
I popped off the little metal cover, covering my idel control screw on the throttle body and turned it back. problem solved.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
IACs go bad all the time but usually don’t show any signs of a defect electrically or physically. Substitution is usually the only way to find out for sure. I have replaced many on several kinds of vehicles when I suspected them to be bad and usually cures the problem.
However I would first do the reset by what PLRX has suggested and look for a possible vacuum leak. Look at the check valve on the right side of the engine under the plastic cover. On some other vehicles, disconnecing the battery and reconnecting has solved the problem too (which is just another form of a reset).
However I would first do the reset by what PLRX has suggested and look for a possible vacuum leak. Look at the check valve on the right side of the engine under the plastic cover. On some other vehicles, disconnecing the battery and reconnecting has solved the problem too (which is just another form of a reset).
Last edited by pcolt94; May 1, 2012 at 09:49 AM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
Did you ever resolve this issue? I have the same issue on my 93 LT1 ZF6. I drop down to ~1000rpm. I am measuring 20-21inHg (on vac gauge) reading from the EGR vac port, My MAP reading corresponds to this in datamaster, my TPS shows 0% at ~.64V in datamaster. ECM is targeting 650rpm according to datamaster. I just tried out a new IAC today and I have the same issue as before. All I can think of is that maybe a PO adjusted that idle screw. If I push on the top of the throttle body valve blades, the idle will drop to what sounds pretty good ( I cant read the tach while I am holding the blades shut) There is no more travel between the throttle and the adjuster screw, I am just stressing the blades shut. How do you go about adjusting this screw, I cant find anything in the FSM about it. What tool do I need? Is it a screwdriver or allen or torx? Do I have to remove the throttle body? The outside end is flat, I it must adjust some other way there is a hole I can access the other end, but none of the tools I have tried seem to engage.
- anyhow the other one is related to the same subject.
