C4 L98 Computer
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Joined: Oct 2007
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C4 L98 Computer
I have a 1987 L98. It has a Chevy Hot Cam. It is also in really good shape. It seems to have a computer idle issue – It cycles from 300 rpm to 700 rpm. I think it is the computer. I understand the 1988 computer is the same, but has a higher clock speed – and it reacts faster.
What is the best computer available for this car?
Also, I have a socketed chip that disables VAT and turns the fan on at a cooler temp.
What mods would be easy and beneficial?
What is the best computer available for this car?
Also, I have a socketed chip that disables VAT and turns the fan on at a cooler temp.
What mods would be easy and beneficial?
Last edited by Frank-in-San-Diego; May 28, 2011 at 11:55 AM.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
The idle jumps that wildly or do you mean from 300-700rpm?
The ECM itself is the last culprit to suspect after everything else has been thoroughly checked out. You need a GM Manual to track down these things.
First thing I'd check is TPS voltage, assuming no codes are set. IAC motor next. Spark, fuel pressure, etc.
Do NOT just throw a new computer at it.
The ECM itself is the last culprit to suspect after everything else has been thoroughly checked out. You need a GM Manual to track down these things.
First thing I'd check is TPS voltage, assuming no codes are set. IAC motor next. Spark, fuel pressure, etc.
Do NOT just throw a new computer at it.
Burning Brakes
Joined: Sep 2004
Posts: 869
Likes: 1
From: Bradford Pa
The idle jumps that wildly or do you mean from 300-700rpm?
The ECM itself is the last culprit to suspect after everything else has been thoroughly checked out. You need a GM Manual to track down these things.
First thing I'd check is TPS voltage, assuming no codes are set. IAC motor next. Spark, fuel pressure, etc.
Do NOT just throw a new computer at it.
The ECM itself is the last culprit to suspect after everything else has been thoroughly checked out. You need a GM Manual to track down these things.
First thing I'd check is TPS voltage, assuming no codes are set. IAC motor next. Spark, fuel pressure, etc.
Do NOT just throw a new computer at it.
start small and work your way it. could be as simple as a bad or misadjusted sensor.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
I had that problem once, and it turned out to be the electronic spark control over by the heater.
when it is erratically idling, try unplugging certain things and the engine will go into the "limp-home" mode.
I unplugged the ESC, and it smoothed out really nice. I shut it off, and plugged it back in, started it up, and it was back. I switched it out with another unit, and it's never been back.
Not that that is your problem, just illustrating it might not be the ECM or the chip.
also, the computer is the same for 1986-1989. There are about 12 different chips for those years.
The 86 chip makes the engine rev high for about 18 seconds, and the newer chips rev it to 1500 for just a few seconds, like 3.
I put an 87 chip in my 86 and I like it.
The best thing is to go to Scott Hanson's website, and get him to burn you a chip. Tell him Chris sent you.
when it is erratically idling, try unplugging certain things and the engine will go into the "limp-home" mode.
I unplugged the ESC, and it smoothed out really nice. I shut it off, and plugged it back in, started it up, and it was back. I switched it out with another unit, and it's never been back.
Not that that is your problem, just illustrating it might not be the ECM or the chip.
also, the computer is the same for 1986-1989. There are about 12 different chips for those years.
The 86 chip makes the engine rev high for about 18 seconds, and the newer chips rev it to 1500 for just a few seconds, like 3.
I put an 87 chip in my 86 and I like it.
The best thing is to go to Scott Hanson's website, and get him to burn you a chip. Tell him Chris sent you.
Last edited by coupeguy2001; May 26, 2011 at 11:57 PM.
