LT1 idles too fast
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Teching In
Joined: Sep 2012
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From: Tallapoosa, Ga.
LT1 idles too fast My 1997 Formula with the Bandit ll package and performance modifications from Arizona Speed and Marine idles when warm around 1300 RPM in park and about 900 RPM 'S in gear. Is there any adjustment at all that is easily adjustable to lower the idle?
Thanks
Thanks
I would start by making sure there is not a lot of carbon built up where the IAC valve pintle moves to allow more/less air flow into the throttle body.
Bandit II package must be a nice one! lol
Bandit II package must be a nice one! lol
Are you going by the factory tach? They are always wrong, always indicate higher than actual. If so, you need to verify that with a scan tool. I get this all the time, "my idle is high", my WOT shift RPM is too high ", etc, etc. Shift itchy 6600, looks like 7000. 800 idle looks like 900 to 1000.
A GOOD scan tool will give you the "Desired Idle" RPM, and the actual RPM. If the RPM at idle is higher than Desired, your IAC counts should be very low. Maybe zero. Desired Idle is what the program calls for. Percent TPS HAS to be zero percent for the PCM to use Desired Idle RPM. If the scan tool shows more than zero percent TPS, you HAVE to fix that. Close the throttle blades. If TPS is zero, RPM is higher than Desired Idle, it is getting air from some where.
Anytime you are checking IAC counts ( or comparing RPM to Desired Idle RPM) make certain it has idled at Least 5 minutes from start up. RPM will be higher at first , as the RPM "decays" (GM's term) after start up. Idle air is added at start up. If you don't wait long enough you are going to chase your tail trying to nail it. This is all on the sheet I send out.
A GOOD scan tool will give you the "Desired Idle" RPM, and the actual RPM. If the RPM at idle is higher than Desired, your IAC counts should be very low. Maybe zero. Desired Idle is what the program calls for. Percent TPS HAS to be zero percent for the PCM to use Desired Idle RPM. If the scan tool shows more than zero percent TPS, you HAVE to fix that. Close the throttle blades. If TPS is zero, RPM is higher than Desired Idle, it is getting air from some where.
Anytime you are checking IAC counts ( or comparing RPM to Desired Idle RPM) make certain it has idled at Least 5 minutes from start up. RPM will be higher at first , as the RPM "decays" (GM's term) after start up. Idle air is added at start up. If you don't wait long enough you are going to chase your tail trying to nail it. This is all on the sheet I send out.
Thread Starter
Teching In
Joined: Sep 2012
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From: Tallapoosa, Ga.
Appreciated very much, I am going by the seat of the pants tach as well as the car tach. After the car is well warmed up it jerks when put into drive or reverse and it will pull up the slight incline from my shop to the road
I have been a Hotrodder all my life and have owned almost fifty noteworthy cars some purchased new and some when they were four or five years old ie. 409 and 427 SS Impalas, 18 Corvettes, five Z/28'S three were new a Hugger Orange car, after reading about the upcoming new 1993 Z//28 for a year I ordered one as soon as available from my dealer himself, my Wife says I had to tell him how to order it but I wound up with a door, window, and power seat delete and order the G92 Perfformance package. My only problem is after having a heart attack followed within a month by three strokes I suffered 100% memory loss and spent two years in a wheelchair. Doctors told my family I would never be any better but after developing my own series of therapy exercises about two hours worth to break loose frozen joints and stretch and strengthen leg muscles I was able to walk with a walking stick more because of my Parkinson's Desease and Rheumatoid Arthritis than anything. Eight months after getting out of the chair I set my first of six Landspeed records in 2010.
I just traded for the 97 Formula Firebird which was all a ground effects and graphics package but the car came with the original window sticker and the Bandit ll came as an option from Pontiac
I have been a Hotrodder all my life and have owned almost fifty noteworthy cars some purchased new and some when they were four or five years old ie. 409 and 427 SS Impalas, 18 Corvettes, five Z/28'S three were new a Hugger Orange car, after reading about the upcoming new 1993 Z//28 for a year I ordered one as soon as available from my dealer himself, my Wife says I had to tell him how to order it but I wound up with a door, window, and power seat delete and order the G92 Perfformance package. My only problem is after having a heart attack followed within a month by three strokes I suffered 100% memory loss and spent two years in a wheelchair. Doctors told my family I would never be any better but after developing my own series of therapy exercises about two hours worth to break loose frozen joints and stretch and strengthen leg muscles I was able to walk with a walking stick more because of my Parkinson's Desease and Rheumatoid Arthritis than anything. Eight months after getting out of the chair I set my first of six Landspeed records in 2010.
I just traded for the 97 Formula Firebird which was all a ground effects and graphics package but the car came with the original window sticker and the Bandit ll came as an option from Pontiac
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Landspeed
did you do modifications, like a Throtle Body, or did the car just start to idle high?
if the later, check for vacume leaks
Also as Ed notes, factory tach is not exact and typically read higher than actual.
did you do modifications, like a Throtle Body, or did the car just start to idle high?
if the later, check for vacume leaks
Also as Ed notes, factory tach is not exact and typically read higher than actual.
Thread Starter
Teching In
Joined: Sep 2012
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From: Tallapoosa, Ga.
I took the car in on a trade for my 37 Chevy HotRod truck which was my daily driver. The car is immaculate inside and out with 71,000 miles and original paint. I have left a message for the original owner to find what performance changed have been made. I know it has an Arizona Speed and Marine mass airflow sensor and throttle body. Equal length headers and a new stainless exhaust, then it has all kind of Hotchkiss suspension components on it. I am going to change it over to synthetic oil, stop a horrific exhaust rattle and drive it. It has a new set of General directional tires. I think it should have a 3:43 rear gear so I might do some test and tune runs, I am guessing mid to low 14'S and I might even do some track events and autocross with it. There is a rattle in the engine when it is cranked cold but it seems I read somewhere that the LT1 engine suffered from piston slap from the time they were new, is that correct? It holds almost 60 lbs. of oil pressure cold and a constant 40 lbs. when warm. I love the body lines and the way it handles, wish it had a little more HP but for my go to daily driver it's not bad
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I cant remember if you have a stick or automatic, but either way you should be low to high 13s, depending on how aggressive you are driving.
For your issue, sounds like you should search the "drill mod" as you are probably missing the idle air passage in the throttle body which can be drilled with an 11/64 drill bit. I dont know much about it, but do a quick search, there were a ton of threads on it recently.
For your issue, sounds like you should search the "drill mod" as you are probably missing the idle air passage in the throttle body which can be drilled with an 11/64 drill bit. I dont know much about it, but do a quick search, there were a ton of threads on it recently.
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Landspeed
Did this high idle problem just happen or has it done it since you got the car?
scan car for IAC counts. If they are higher than 30-35 at idle, car warmed up, you need to make TB adjustments to bring down.
The "drill mod" and cracking open TB blades slightly are two ways of doing that. Again you need a scan tool to read IAC counts while making these adjustments to see how far to adjust/dril. If you do drill your ASM TB, start with 1/8" hole and go 1/64" larger if needed. take baby steps, 1/64" makes a big diffrence.
with a aftermarket TB & MAF the car should have a aftermarket PCM tune to accomadate those and possibly cam, larger injectors, etc. if the motor has those upgrades. The car doesn't need a larger TB or MAF without heads/cam, cu in so I assume you have them.
if your idle issue just occured and was fine before than check for vacume leaks
Did this high idle problem just happen or has it done it since you got the car?
scan car for IAC counts. If they are higher than 30-35 at idle, car warmed up, you need to make TB adjustments to bring down.
The "drill mod" and cracking open TB blades slightly are two ways of doing that. Again you need a scan tool to read IAC counts while making these adjustments to see how far to adjust/dril. If you do drill your ASM TB, start with 1/8" hole and go 1/64" larger if needed. take baby steps, 1/64" makes a big diffrence.
with a aftermarket TB & MAF the car should have a aftermarket PCM tune to accomadate those and possibly cam, larger injectors, etc. if the motor has those upgrades. The car doesn't need a larger TB or MAF without heads/cam, cu in so I assume you have them.
if your idle issue just occured and was fine before than check for vacume leaks
If the throttle angle does not show zero percent on the scan tool it will not slow down. The PCM will be using the throttle follower IAC position number tables, not using the base idle speed Vs Coolant Temp tables.
High idle speed, with high IAC counts means the PCM is not trying to make it idle at the Desired Idle number on the scan tool.
If it idles too slow, that is when it needs more air. If the PCM is trying to make it idle down to the Desired Idle number displayed on the scan tool, the IAC numbers will be very low, down to zero or close.
High idle speed, with high IAC counts means the PCM is not trying to make it idle at the Desired Idle number on the scan tool.
If it idles too slow, that is when it needs more air. If the PCM is trying to make it idle down to the Desired Idle number displayed on the scan tool, the IAC numbers will be very low, down to zero or close.
Thread Starter
Teching In
Joined: Sep 2012
Posts: 29
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From: Tallapoosa, Ga.
Thanks for all the advice all of you are very knowledgeable
About the LT engines, I could set the time and adjust a Holley or Carter AFB from the first time I ran down a dragstrip in a Corvette when I was 16. Having landspeed raced a Chevy truck with a LQ9 engine and dragraced it and my Corvette with an LS motor I have at least gotten familiar enough with them I can talk the talk but I have to leave the tuneups to the guy with a dyno and a laptop.My Corvette makes over 400 HP to the rear wheels and will get 26 MPG on the road a far cry from the days of a car that would not idle at a traffic light, foul spark plugs and get 10 MPG or less. Maybe I need to take the Firebird to my Tuner and let them check it out. I love the way the car handles and it runs pretty strong, feels like more than 275 HP. I know the Bandit ll package sounds kind of corny but that ground effects package looks great on the car.
This forum has so many forums within I am not sure where to go on certain items I would like to run an 8 to 10 MPH top speed loss after adding 75HP to the high RPM range to the experts and I would love to find a volunteer to post some pictures of the Firebird in an appropriate place, any suggestions?
Thanks everyone
Oh , don't know if there are still any NASCAR fans left but I have a NASCAR history and connection and in a time of weakness I used to drive a drag race car for a dealership.
About the LT engines, I could set the time and adjust a Holley or Carter AFB from the first time I ran down a dragstrip in a Corvette when I was 16. Having landspeed raced a Chevy truck with a LQ9 engine and dragraced it and my Corvette with an LS motor I have at least gotten familiar enough with them I can talk the talk but I have to leave the tuneups to the guy with a dyno and a laptop.My Corvette makes over 400 HP to the rear wheels and will get 26 MPG on the road a far cry from the days of a car that would not idle at a traffic light, foul spark plugs and get 10 MPG or less. Maybe I need to take the Firebird to my Tuner and let them check it out. I love the way the car handles and it runs pretty strong, feels like more than 275 HP. I know the Bandit ll package sounds kind of corny but that ground effects package looks great on the car.
This forum has so many forums within I am not sure where to go on certain items I would like to run an 8 to 10 MPH top speed loss after adding 75HP to the high RPM range to the experts and I would love to find a volunteer to post some pictures of the Firebird in an appropriate place, any suggestions?
Thanks everyone
Oh , don't know if there are still any NASCAR fans left but I have a NASCAR history and connection and in a time of weakness I used to drive a drag race car for a dealership.