C4 Corvette Rough Idle Normal?
Thread Starter
Heel & Toe
Joined: Nov 2022
Posts: 23
Likes: 1
From: Naples
C4 Corvette Rough Idle Normal?
Hey guys so i got a quick question i have a 1996 C4 Corvette LT1
Its got a bunch of new things everything within ignition and sparks and such have been replaced i was chasing a rough-ish idle for about 5 months and $8000 later including a new trans and torq converter she still has a kinda shaken idle nothing crazy!
I was really thinking then i thought omg what if it was just motor mounts but my main question is i know it’s a basically 30 year old engine do most have a shake at idle?
Its got a bunch of new things everything within ignition and sparks and such have been replaced i was chasing a rough-ish idle for about 5 months and $8000 later including a new trans and torq converter she still has a kinda shaken idle nothing crazy!
I was really thinking then i thought omg what if it was just motor mounts but my main question is i know it’s a basically 30 year old engine do most have a shake at idle?
Cruising
Joined: Apr 2023
Posts: 12
Likes: 3
From: Ohio
No, unless it has a hotter cam, it shouldn't. Now as to finding the reason, that's a bit harder. I just got done chasing my idle, performance issue down in an L98 and after new fuel filter, de-carboning the engine, cap, rotor timing adjust, knock sensor. I discovered mine was the timing module.ultimately. It can get crazy, I read one guy who posted somewhere his cigarette lighter didn't work and after fixing the ground, discovered it also fixed the signal through the brake switch to activate the torque converter locking.
Moderator, Tech Contributor
Joined: Sep 2013
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Likes: 4,020
From: Cape Coral, Florida
Hey guys so i got a quick question i have a 1996 C4 Corvette LT1
Its got a bunch of new things everything within ignition and sparks and such have been replaced i was chasing a rough-ish idle for about 5 months and $8000 later including a new trans and torq converter she still has a kinda shaken idle nothing crazy!
I was really thinking then i thought omg what if it was just motor mounts but my main question is i know it’s a basically 30 year old engine do most have a shake at idle?
Its got a bunch of new things everything within ignition and sparks and such have been replaced i was chasing a rough-ish idle for about 5 months and $8000 later including a new trans and torq converter she still has a kinda shaken idle nothing crazy!
I was really thinking then i thought omg what if it was just motor mounts but my main question is i know it’s a basically 30 year old engine do most have a shake at idle?
A bunch of things can cause a rough idle…I see your in Florida so if you’re near me in the Southwest bring the car by and I’ll take a look at it for you…a scan tool is needed to diagnose this…if not using one you’ll just be guessing.
Zen Vet Master Level VII
Joined: Mar 2016
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From: Southlake, TX
Thread Starter
Heel & Toe
Joined: Nov 2022
Posts: 23
Likes: 1
From: Naples
Hey man yeah i’m in Naples Florida actually if you wanna shoot me a message i would love for someone to maybe look at it like i said the car was in the shop for 5 months
New Ecm
new ICM
new fuel pump
new fuel filter
new fuel injectors
and a bunch more
but if you can shoot me a dm id love to have you look at it
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,540
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From: Cape Coral, Florida
Hey man yeah i’m in Naples Florida actually if you wanna shoot me a message i would love for someone to maybe look at it like i said the car was in the shop for 5 months
New Ecm
new ICM
new fuel pump
new fuel filter
new fuel injectors
and a bunch more
but if you can shoot me a dm id love to have you look at it
New Ecm
new ICM
new fuel pump
new fuel filter
new fuel injectors
and a bunch more
but if you can shoot me a dm id love to have you look at it
Will send a PM !!…5 months in a shop and all those parts ??…if it was a general repair shop or a dealership they just replace parts until they get lucky…99.99% of them don’t know how to diagnose unfortunately….would like to know what the other “bunch” was…LOL !!
Thread Starter
Heel & Toe
Joined: Nov 2022
Posts: 23
Likes: 1
From: Naples
This doesn’t include the rebuilt trans and new upgraded torq converter
Thread Starter
Heel & Toe
Joined: Nov 2022
Posts: 23
Likes: 1
From: Naples
Can you put up a video of the engine at idle? We all have different ideas on what constitutes a shake. Our engines all have a little movement but some of us are more attuned to the movement. You could have a problem or be just fine. Put up a video and we can take a look.
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Moderator, Tech Contributor
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From: Cape Coral, Florida
HOLY CRAP !!…well this is what happens when shops don’t know how to diagnose...they just guess !!…I don’t care what was changed so I don’t base my diagnosis on that…I’d be looking for a EGR valve that may be stuck open or partially open giving you a rough idle and the car runs better above idle…saw in a previous post you had some starting issues…classic stuck open EGR…I’d be looking for elevated fuel trims and lower engine vacuum…also the solenoid is duty cycle controlled so I’ll be looking at that too.
Last edited by C5 Diag; Apr 18, 2023 at 07:07 AM.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
OP is bringing his car by this weekend….I do a relative compression on EVERY car I look at and everything will be checked and a 100% diagnosis’ guaranteed…LOL !!
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From: Cape Coral, Florida
Cruising
Joined: Apr 2023
Posts: 12
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From: Ohio
Some of still live in the stone age and don't have fancy equipment, LOL. Not to hijack the thread, but since you seem to have the knowledge .... My 1987 L98 has no power reading to either side of the dual brake/cruise switch on the cruise part. I was thinking I could run a 12v hot to it and see if my cruise works. I don't know where I can get a wiring diagram to pull the cruise column wires and add an new ssh mount switch. .Even in PM, thoughts would be appreciated. Thread ... https://www.corvetteforum.com/forums...ke-switch.html
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,540
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From: Cape Coral, Florida
Some of still live in the stone age and don't have fancy equipment, LOL. Not to hijack the thread, but since you seem to have the knowledge .... My 1987 L98 has no power reading to either side of the dual brake/cruise switch on the cruise part. I was thinking I could run a 12v hot to it and see if my cruise works. I don't know where I can get a wiring diagram to pull the cruise column wires and add an new ssh mount switch. .Even in PM, thoughts would be appreciated. Thread ... https://www.corvetteforum.com/forums...ke-switch.html
Advanced
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From: Central Florida
Moderator, Tech Contributor
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From: Cape Coral, Florida
Advanced
Joined: May 2022
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From: Central Florida
Shake started a few months ago, but not seemingly related or in correlation with any work performed.
Higher rpm feels good. 94 6spd. Mileage could be better, around 17-18 city. Daily driver.
I did the injector test, disconnecting one at a time, and #2 shows no significant change in idle when disconnected. That was going to be my next potential source, but haven’t gotten around to that yet.
Been running Mystery Oil through it, and that improved mileage substantially. At that time, it was at 15-16 city.
Racer
Joined: Jul 2012
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From: Northeast Ohio
Setup a YouTube account and upload to there, then post the link here. When you upload the video to YouTube you can also set the privacy to not be public. This will let people that you give the link to view the video, but it won't be available to the rest of the world even it they go directly to your channel.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
Absolutely. Been chasing a low rpm (~1200) shake for a while. Opti is new, needed as it was throwing codes. Wires plugs last year. Lets just say all sensors as well.
Shake started a few months ago, but not seemingly related or in correlation with any work performed.
Higher rpm feels good. 94 6spd. Mileage could be better, around 17-18 city. Daily driver.
I did the injector test, disconnecting one at a time, and #2 shows no significant change in idle when disconnected. That was going to be my next potential source, but haven’t gotten around to that yet.
Been running Mystery Oil through it, and that improved mileage substantially. At that time, it was at 15-16 city.
Shake started a few months ago, but not seemingly related or in correlation with any work performed.
Higher rpm feels good. 94 6spd. Mileage could be better, around 17-18 city. Daily driver.
I did the injector test, disconnecting one at a time, and #2 shows no significant change in idle when disconnected. That was going to be my next potential source, but haven’t gotten around to that yet.
Been running Mystery Oil through it, and that improved mileage substantially. At that time, it was at 15-16 city.
Last edited by C5 Diag; Apr 26, 2023 at 01:26 PM.