L98 High idle issue
Thread Starter
Heel & Toe
Joined: Nov 2015
Posts: 23
Likes: 0
L98 High idle issue
hello i have an 87 L98, the idling is everywhere, it goes really high to high haha, ranges from 1800-1500RPM. ive been checking for vacuum leaks, but cant seem to successfully find any. i did go through the readjustment process of the accelerator screw, because the previous owner did mess with it. also adjusted the TPS. any idea on what it could be, or what i can do to find out what the problem is?
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Hook it up to a scanner and see if it is really doing that RPM or whether you think it is doing it. See IAC counts. If it is 0 and you unscrew the adjustment screw, rev and it doesn't go up, you have a leak.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
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Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
First off, that procedure is only good for a car that is 100% working. No air leaks, no bad wires, plugs, dirty injectors and most importantly, 100% accurate tach. Kinda why I usually dismiss the FSM method. If your tach is off, you adjust off. You don't really know what the ECM is seeing unless you have a scanner. If so, why not go the entire way and adjust via IAC counts which are going to be better and give you a good hint of an air leak?
Thread Starter
Heel & Toe
Joined: Nov 2015
Posts: 23
Likes: 0
First off, that procedure is only good for a car that is 100% working. No air leaks, no bad wires, plugs, dirty injectors and most importantly, 100% accurate tach. Kinda why I usually dismiss the FSM method. If your tach is off, you adjust off. You don't really know what the ECM is seeing unless you have a scanner. If so, why not go the entire way and adjust via IAC counts which are going to be better and give you a good hint of an air leak?
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
I cannot understand why people are so adverse to putting a scanner on their cars and prefer to rely on guessing games to tell what is going on. Someone who tunes can tell you whether the MAF is getting a plausable value or what the ECM sees the engine temp is. With a timing light, we can see if the distributor has been moved or have an idea as to whether the Harmonic Balancer is suspect. Timing can affect idle as can air leaks. Engine temp can also affect idle. Fuel pressure should be checked. Ask someone in the scan and tune section what the plausible values for MAF is. If your IAC counts are 0, you either have an air leak or turned the screw in too much. That is a possibility worth mentioning.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Because most of the members here don't have a scan tool laying around and a volt meter was common and cheap to get if you don't have one.
I use a scan tool but again most don't have them. Especially for obd1. Obd2 is cheap and plentiful but obd1 is expensive and much harder to even find these days.
I use a scan tool but again most don't have them. Especially for obd1. Obd2 is cheap and plentiful but obd1 is expensive and much harder to even find these days.
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
The idle procedure is a pita. But it have all steps followed.
I unscrew the screw out before starting the procedure. I think you need to
Idle the car at 450 or so just so the computer can idle the car up, because it can't idle the car down. So thus it barely running during the procedure. I posted the procedure a few times here with tips and haven't had to adjust it over a yr now. Tps sensor must be reset anytime the throttle screw is moved because the computerneeds to know when your foot is off the gas. Pretty basic computing .
I unscrew the screw out before starting the procedure. I think you need to
Idle the car at 450 or so just so the computer can idle the car up, because it can't idle the car down. So thus it barely running during the procedure. I posted the procedure a few times here with tips and haven't had to adjust it over a yr now. Tps sensor must be reset anytime the throttle screw is moved because the computerneeds to know when your foot is off the gas. Pretty basic computing .
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Because most of the members here don't have a scan tool laying around and a volt meter was common and cheap to get if you don't have one.
I use a scan tool but again most don't have them. Especially for obd1. Obd2 is cheap and plentiful but obd1 is expensive and much harder to even find these days.
I use a scan tool but again most don't have them. Especially for obd1. Obd2 is cheap and plentiful but obd1 is expensive and much harder to even find these days.
My scanner is an Auto X-ray for both and I also have a Snap On Brick and I also have Datamaster. Although I don't care for it much. Still like the Auto X-ray better than the Datamaster.
Thread Starter
Heel & Toe
Joined: Nov 2015
Posts: 23
Likes: 0
The idle procedure is a pita. But it have all steps followed.
I unscrew the screw out before starting the procedure. I think you need to
Idle the car at 450 or so just so the computer can idle the car up, because it can't idle the car down. So thus it barely running during the procedure. I posted the procedure a few times here with tips and haven't had to adjust it over a yr now. Tps sensor must be reset anytime the throttle screw is moved because the computerneeds to know when your foot is off the gas. Pretty basic computing .
I unscrew the screw out before starting the procedure. I think you need to
Idle the car at 450 or so just so the computer can idle the car up, because it can't idle the car down. So thus it barely running during the procedure. I posted the procedure a few times here with tips and haven't had to adjust it over a yr now. Tps sensor must be reset anytime the throttle screw is moved because the computerneeds to know when your foot is off the gas. Pretty basic computing .