High/Low idle - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
 
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post #1 of 10 (permalink) Old 01-22-2017, 10:45 PM Thread Starter
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If got an interesting case hear (1994 z28 6mt) car loves to idle high! First start of the day ( second attempt car Nevers starts first try starts second try effortlessly) car idles at 1500 rpm and won't go down no matter how long I sit their !maybe it will drop like 100-200 rpm if I'm Lucky. I have a 58mm bbk tb I've messed with the adjustment screw I've sprayed the entire engine (all vacum lines) with carb cleaner in hope of finding a vacuum leak but found nothing my only other guess is the IAC possibly. It does not end there when turning off the engine it makes a lot of noise because its getting so much gas due to the high idle but the weird part is when I start the car hot it idles extremely low to the point where I have to peddle it so it doesn't die and then eventually it goe back to idling at 1500 at hot start it idles about (200-600 rpm). Me and my dad are puzzled. Recently changed the fuel pressure regulator and fue pump is a new Bosch one. Any input is appreciated. Car is drivable but drinks a load of gas which isn't cheap filling up with premium.

Last edited by frankmolinas; 01-22-2017 at 10:53 PM.
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post #2 of 10 (permalink) Old 01-23-2017, 12:18 PM
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aftermarket TB's generally have idle issues. If you have the stock TB....might want to put that back on to see if your issue goes away.

A scan tool that reads IAC counts will help. If they are pegged at 160, especially when your idle does drop, you need to do one of two "fix" methods to the 58 mm. This requires a scan tool to read IAC counts as you mod the 58 mm. You either drill a hole where the stock one has one or crack the TB blades open and then drill/slot the TPS housing. The later I don't endorse but people have done it that way. Do not blindly do either without having the ability to scan/read IAC counts

IAC counts want to be 30-35 (32) at idle with engine at operating temp. TPS volts want to be .67 vdc blades closed and 4.5 vdc full open. volts should increase evenly and smoothly when you open the TB blades

also after you start the car and it runs for a moment, shut off, and then pull the rubber elbow from back of FPR....is there any sign of fuel in it? if yes FPR is bad....although not really why idle issue is FU. More the fuel smell you have and hard 1st start attempt.
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post #3 of 10 (permalink) Old 01-23-2017, 12:59 PM
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Do you have the cable and the proper program to hook up to the car? Scan it and see what it wants you to know.

1995 LT1 Wagon. ERE 383
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post #4 of 10 (permalink) Old 01-23-2017, 07:05 PM
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I agree with AtlantaDan, if you don't scan it, you are just guessing and could spend a lot of money and time not on the solution. There is a Free download called Scan94/95 that works really good, but you need a specific cable and a Laptop.

To download the Free software and read the info on how to hook it up and the cable, go to the 4th Gen F-Body forum at this website and go to the Sticky with the Free Download from Gary Doug on OBD1 software. This is the link to the website that the download is at https://www.mediafire.com/?0elo4c935uc5s

Also, go to http://shbox.com/page/index.html for a lot of info with pictures and testing and all kinds of stuff.

Hope you get this figured out, it can be really frustrating.

95 Z28, Automatic, Stock except for CAI, Throttle Body Bypass, Flowmaster Exhaust. 2:73 Rear, SLP Fan Control, 145k Miles - Runs Great

Last edited by garybo; 01-23-2017 at 07:37 PM.
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post #5 of 10 (permalink) Old 01-24-2017, 07:03 AM
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You can download the scan program called "scan9495" in the 4th gen section sticky threads. The program reads regular codes, ABS & SIR codes. Does running sensor scans and will log data to a file for later playback. It also tests engine & auto trans actuators. And it's free.

You will need a cable to connect your pc based computer to car's aldl. Get at OBD Diagnostics

You might also want to check your fuel injectors for proper spray pattern and leakage. Use new o-rings after pulling fuel rail out of engine.
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post #6 of 10 (permalink) Old 01-25-2017, 09:34 PM Thread Starter
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Quote:
Originally Posted by BALLSS View Post
aftermarket TB's generally have idle issues. If you have the stock TB....might want to put that back on to see if your issue goes away.

A scan tool that reads IAC counts will help. If they are pegged at 160, especially when your idle does drop, you need to do one of two "fix" methods to the 58 mm. This requires a scan tool to read IAC counts as you mod the 58 mm. You either drill a hole where the stock one has one or crack the TB blades open and then drill/slot the TPS housing. The later I don't endorse but people have done it that way. Do not blindly do either without having the ability to scan/read IAC counts

IAC counts want to be 30-35 (32) at idle with engine at operating temp. TPS volts want to be .67 vdc blades closed and 4.5 vdc full open. volts should increase evenly and smoothly when you open the TB blades

also after you start the car and it runs for a moment, shut off, and then pull the rubber elbow from back of FPR....is there any sign of fuel in it? if yes FPR is bad....although not really why idle issue is FU. More the fuel smell you have and hard 1st start attempt.


So the person that sold me the car let me know that he had an extra intake manifold with throttling body egr valve IAC TPS and MAP sensors he sold it to me for 40 bucks. I swapped out all the sensors and reset my pcm ( left battery unplugged for 15ish minutes) come to start my car and immediately it starts up idling at 1250 cold (way lower than before) took if for a spin and it was idling at about 1500 in neutral at usual than after about a mile of driving I was cruising in neutral and the idle dropped to 1000 ( happiest I've been in a long time) the car stayed idling at 1000 the whole time. I have a vacuum leak in my intake elbow it's the original and cracked to pieces so after I replace that hopefully it idles even lower! Fingers crossed if Tommorow morning it idles at 1250 when cold then 1000 after warming up I'll be confident I fixed the problem! Thanks for the advice guys.
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post #7 of 10 (permalink) Old 01-28-2017, 07:03 AM
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FWIW, an idle of 1,000 is still very high for a stock car. Seems like you are on the right track, though.

1995 LT1 Wagon. ERE 383
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post #8 of 10 (permalink) Old 01-28-2017, 11:25 AM
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Quote:
Originally Posted by frankmolinas View Post
I have a vacuum leak in my intake elbow it's the original and cracked to pieces so after I replace that hopefully it idles even lower!.
that will absolutely cause a high idle if the intake elbow is cracked and leaking
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post #9 of 10 (permalink) Old 01-28-2017, 09:02 PM Thread Starter
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Ported heads, and intake , 58mm TB, long tube headers 1.7 rockers. Would any of those cause a higher than normal idle. Plus I have a vacuum leak from my intake elbow that I need to fix (96 dollars for a ****ing piece of rubber).
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post #10 of 10 (permalink) Old 01-29-2017, 09:23 AM
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Quote:
Originally Posted by frankmolinas View Post
Ported heads, and intake , 58mm TB, long tube headers 1.7 rockers. Would any of those cause a higher than normal idle. Plus I have a vacuum leak from my intake elbow that I need to fix (96 dollars for a ****ing piece of rubber).
As BALLSS said, a vacuum leak will definitely cause a high idle. Intake elbow: I had this one on my last wagon and it was totally fine. $35

What are the other engine specs? A 58mm tb and 1.7's? That is a shitload of air for a street car. Usually those mods come with a fat camshaft, and if that's the case - your idle probably was set in the tune to be 1k or so.

1995 LT1 Wagon. ERE 383
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