Rough Idle
Thread Starter
Pro
Joined: Sep 2007
Posts: 534
Likes: 0
From: Chandler AZ
Rough Idle
Hey everyone in C4 land,
Been having a minor issue with my engine at idle. Normally she'll idle anywhere from 600-800 RPM, now I'm lucky if the engine will sit below 1000. At a dead stop with my foot on the brakes sometimes it'll "jump", and almost break free from the brakes it feels like. The first time it did this it did break free and move a few feet until I caught it and learned to keep my foot down. Now it'll just jump once in awhile and sound like she's constantly being revved.
New distributor, plugs and wires <1000 miles ago. 134k on the clock. Stock 94 LT1. No codes as far as I can see.
Responses are much appreciated
Been having a minor issue with my engine at idle. Normally she'll idle anywhere from 600-800 RPM, now I'm lucky if the engine will sit below 1000. At a dead stop with my foot on the brakes sometimes it'll "jump", and almost break free from the brakes it feels like. The first time it did this it did break free and move a few feet until I caught it and learned to keep my foot down. Now it'll just jump once in awhile and sound like she's constantly being revved.
New distributor, plugs and wires <1000 miles ago. 134k on the clock. Stock 94 LT1. No codes as far as I can see.
Responses are much appreciated
Instructor
Joined: Sep 2009
Posts: 194
Likes: 1
From: Northwest Indiana
Hey Catts:
I have a '92 that I'm still working similar bugs out of. When I first got it, my car would idle at around 1,000 - 1,100 in gear and 1,500 - 1,700 in park. Yeah, no fun.
I put a new idle air control valve in mine and it corrected the idle situation for the most part. The IAC is on the passenger side of the throttle body on my '92, and I believe it should be the same for your '94. The opening in the throttle body that the IAC fits into can become clogged with carbon deposits and cause the IAC pintel to stick causing major idle problems. My mechanic tried cleaning my IAC, but the high idle situation ended up coming back, so I just replaced it. A new IAC shouldn't run you more than about $60 - $80.
My recommendation would be to remove your throttle body entirely, remove the IAC and the throttle positioning sensor from the throttle body, and then give the TB a good cleaning inside and out with some good spray throttle body cleaner and a gentle scrubbing with an old tooth brush. Be sure to thoroughly flush out the IAC port and scrub the TB butterflies. You'll want to make sure you remove as much of that nasty black carbon foulng as possible. Make sure that the butterflies open and close easily by hand. As I mentioned, you can try cleaning the exisiting IAC by spraying a little TB cleaner ON THE TOOTHBRUSH and then use the toothbrush to GENTLY scrub the pintel (pointed end) on the IAC. You can also put a little WD40 on the pintel as well to help it move. Or, you can just replace it with a new unit. Put everything back together using a NEW gasket where the TB mounts against the intake manifold. Fire it up and see how she runs.
Good luck!
Ron
I have a '92 that I'm still working similar bugs out of. When I first got it, my car would idle at around 1,000 - 1,100 in gear and 1,500 - 1,700 in park. Yeah, no fun.
I put a new idle air control valve in mine and it corrected the idle situation for the most part. The IAC is on the passenger side of the throttle body on my '92, and I believe it should be the same for your '94. The opening in the throttle body that the IAC fits into can become clogged with carbon deposits and cause the IAC pintel to stick causing major idle problems. My mechanic tried cleaning my IAC, but the high idle situation ended up coming back, so I just replaced it. A new IAC shouldn't run you more than about $60 - $80.
My recommendation would be to remove your throttle body entirely, remove the IAC and the throttle positioning sensor from the throttle body, and then give the TB a good cleaning inside and out with some good spray throttle body cleaner and a gentle scrubbing with an old tooth brush. Be sure to thoroughly flush out the IAC port and scrub the TB butterflies. You'll want to make sure you remove as much of that nasty black carbon foulng as possible. Make sure that the butterflies open and close easily by hand. As I mentioned, you can try cleaning the exisiting IAC by spraying a little TB cleaner ON THE TOOTHBRUSH and then use the toothbrush to GENTLY scrub the pintel (pointed end) on the IAC. You can also put a little WD40 on the pintel as well to help it move. Or, you can just replace it with a new unit. Put everything back together using a NEW gasket where the TB mounts against the intake manifold. Fire it up and see how she runs.
Good luck!
Ron
Thread Starter
Pro
Joined: Sep 2007
Posts: 534
Likes: 0
From: Chandler AZ
Hey Catts:
I have a '92 that I'm still working similar bugs out of. When I first got it, my car would idle at around 1,000 - 1,100 in gear and 1,500 - 1,700 in park. Yeah, no fun.
I put a new idle air control valve in mine and it corrected the idle situation for the most part. The IAC is on the passenger side of the throttle body on my '92, and I believe it should be the same for your '94. The opening in the throttle body that the IAC fits into can become clogged with carbon deposits and cause the IAC pintel to stick causing major idle problems. My mechanic tried cleaning my IAC, but the high idle situation ended up coming back, so I just replaced it. A new IAC shouldn't run you more than about $60 - $80.
My recommendation would be to remove your throttle body entirely, remove the IAC and the throttle positioning sensor from the throttle body, and then give the TB a good cleaning inside and out with some good spray throttle body cleaner and a gentle scrubbing with an old tooth brush. Be sure to thoroughly flush out the IAC port and scrub the TB butterflies. You'll want to make sure you remove as much of that nasty black carbon foulng as possible. Make sure that the butterflies open and close easily by hand. As I mentioned, you can try cleaning the exisiting IAC by spraying a little TB cleaner ON THE TOOTHBRUSH and then use the toothbrush to GENTLY scrub the pintel (pointed end) on the IAC. You can also put a little WD40 on the pintel as well to help it move. Or, you can just replace it with a new unit. Put everything back together using a NEW gasket where the TB mounts against the intake manifold. Fire it up and see how she runs.
Good luck!
Ron
I have a '92 that I'm still working similar bugs out of. When I first got it, my car would idle at around 1,000 - 1,100 in gear and 1,500 - 1,700 in park. Yeah, no fun.
I put a new idle air control valve in mine and it corrected the idle situation for the most part. The IAC is on the passenger side of the throttle body on my '92, and I believe it should be the same for your '94. The opening in the throttle body that the IAC fits into can become clogged with carbon deposits and cause the IAC pintel to stick causing major idle problems. My mechanic tried cleaning my IAC, but the high idle situation ended up coming back, so I just replaced it. A new IAC shouldn't run you more than about $60 - $80.
My recommendation would be to remove your throttle body entirely, remove the IAC and the throttle positioning sensor from the throttle body, and then give the TB a good cleaning inside and out with some good spray throttle body cleaner and a gentle scrubbing with an old tooth brush. Be sure to thoroughly flush out the IAC port and scrub the TB butterflies. You'll want to make sure you remove as much of that nasty black carbon foulng as possible. Make sure that the butterflies open and close easily by hand. As I mentioned, you can try cleaning the exisiting IAC by spraying a little TB cleaner ON THE TOOTHBRUSH and then use the toothbrush to GENTLY scrub the pintel (pointed end) on the IAC. You can also put a little WD40 on the pintel as well to help it move. Or, you can just replace it with a new unit. Put everything back together using a NEW gasket where the TB mounts against the intake manifold. Fire it up and see how she runs.
Good luck!
Ron
White on red is the only way to go
Instructor
Joined: Sep 2009
Posts: 194
Likes: 1
From: Northwest Indiana
Cool! Let us know how it works out for you!
One more thing; when you're disconnecting the coolant hoses on either side of your throttle body, be sure to stuff a bunch of rags or something underneath them to catch or absorb any coolant that might still be in there when you pull them off. Your Optispark is sitting right underneath your TB and you DON'T want any coolant leaking down into that baby!
One more thing; when you're disconnecting the coolant hoses on either side of your throttle body, be sure to stuff a bunch of rags or something underneath them to catch or absorb any coolant that might still be in there when you pull them off. Your Optispark is sitting right underneath your TB and you DON'T want any coolant leaking down into that baby!
Instructor
Joined: Sep 2009
Posts: 194
Likes: 1
From: Northwest Indiana
Oh, one more thing. I guess I probably should have mentioned this in my first reply. Be sure to check all of your vacuum lines while you're doing the other work. Loose/leaky vacuum lines can cause high idle problems. Give them all a visual inspection for any cracks and make sure they seal well where they connect.
Hmmm? I need to start listening to my own advice.
Maybe my own 'Vette will run better!
Hmmm? I need to start listening to my own advice.
Maybe my own 'Vette will run better!
Heel & Toe
Joined: Feb 2010
Posts: 17
Likes: 0
From: Cartersville GA
Same issue here
Same issue here, working through it. Idles around 7-800, jumps to 1k and leaves me thinkng that if I didn't have my foot on the brake well enough, i would be in the middle of the intersection. I'm new to the vettes, this my first. I just got it yesterday, and this is my main issue.
I just love this thing and want to make sure I do everything correctly. I will follow some of this advice and see if the cleaning/replacement of the IAC helps. I'll definately clean the TB or have someone look at it. My only concern is that I've not worked on the vettes before. Worked on all kinds of other cars, but vettes...new. "When all else fails, follow the directions"...lol. Think I'll have a someone "'supervise" what I'm doing when I do. I'm in no hurry. Better safe than sorry.
I just love this thing and want to make sure I do everything correctly. I will follow some of this advice and see if the cleaning/replacement of the IAC helps. I'll definately clean the TB or have someone look at it. My only concern is that I've not worked on the vettes before. Worked on all kinds of other cars, but vettes...new. "When all else fails, follow the directions"...lol. Think I'll have a someone "'supervise" what I'm doing when I do. I'm in no hurry. Better safe than sorry.
