M6 Idle questions
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Launching!
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From: Milwaukee, Wisconsin
M6 Idle questions I have two quick questions -
I just picked up a 30th anniversary 97 z28 M6. The car is idling at about 1000-1200 rpm which seems high. After searching around I saw that the factory idle should be around 800rpm for a M6 car right? I went over everything and I can't seem to find anything wrong, no vacuum leaks, nothing missing, TB screw is set properly...
Where should I look to get the idle back down where it should be? There are no check engine codes and the car runs great, just idles a bit high.
I also just installed a ported & polished 52mm stock throttle body with an SLP airfoil, and i'm having a problem with that as well. To be clear, the high idle was happening right away with the car totally stock, and is still doing it with the new throttle body so it's not something that was caused by swapping the TB. Anyway, with the new TB, when I'm driving normally under partial throttle it's getting stuck open when I take off the gas. It will stay idling at 1200-1500 when coasting out of gear or at a stop. It's nothing physical meaning the blades are not getting stuck on anything, neither is the cable or anything like that. It seems like it's almost vacuum related where there is a pressure keeping it open somehow. If I blip the throttle hard it will come fully closed and be fine, but I don't want to have to do that constantly.
Has anyone ever heard of this or know how to fix it?
I just picked up a 30th anniversary 97 z28 M6. The car is idling at about 1000-1200 rpm which seems high. After searching around I saw that the factory idle should be around 800rpm for a M6 car right? I went over everything and I can't seem to find anything wrong, no vacuum leaks, nothing missing, TB screw is set properly...
Where should I look to get the idle back down where it should be? There are no check engine codes and the car runs great, just idles a bit high.
I also just installed a ported & polished 52mm stock throttle body with an SLP airfoil, and i'm having a problem with that as well. To be clear, the high idle was happening right away with the car totally stock, and is still doing it with the new throttle body so it's not something that was caused by swapping the TB. Anyway, with the new TB, when I'm driving normally under partial throttle it's getting stuck open when I take off the gas. It will stay idling at 1200-1500 when coasting out of gear or at a stop. It's nothing physical meaning the blades are not getting stuck on anything, neither is the cable or anything like that. It seems like it's almost vacuum related where there is a pressure keeping it open somehow. If I blip the throttle hard it will come fully closed and be fine, but I don't want to have to do that constantly.
Has anyone ever heard of this or know how to fix it?
I got the idle right at 900 were my tune is set but like your said crusing take it out of gear it stays at a higher idle untill i come to a stop so I hope someone chimes In on this
Thread Starter
Launching!
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From: Milwaukee, Wisconsin
Yeah it's strange, I've been asking my car buddies and heard a few similar problems and they said it was vacuum related, where the TB had formed a vacuum that was keeping the blades from closing till it dissipated.
Not sure if this is my problem or not, it sounds like it though, but I don't know how to go about fixing it. I'm going to mess around with the set screw tomorrow and see if it makes a difference, also going to clean the IAC.
Not sure if this is my problem or not, it sounds like it though, but I don't know how to go about fixing it. I'm going to mess around with the set screw tomorrow and see if it makes a difference, also going to clean the IAC.
Based off what you have said so far (the RPMs hanging high and coming down, high idle), I definitely suspect a vacuum leak of some sort. Any chance intake manifold gasket could be bad? Give your motor a reallllly good once over. Here are suspect places to check...
Front and back sides of the intake manifold
All vacuum lines running to and from manifold.
PCVs
IAC
TB Gasket
Fuel Injector Orings
Front and back sides of the intake manifold
All vacuum lines running to and from manifold.
PCVs
IAC
TB Gasket
Fuel Injector Orings
Yeah, my 95 Formula idles at about 1000 rpm and hangs at 1500 rpm if I coast out of gear. Reset the IAC a couple of times, checked the pigtail voltages, checked ohms on my IAC, all my vacuum hoses, etc., couldn't find any leaks, bad gaskets, anything.
Try pushing down on the intake manifold and see if the problem can be reproduced. I've found that just a bit of downward pressure can make the difference in tiny intake manifold leaks.
Has the car ever been tuned or is it still stock?
For all hoses, check to see if they are hard/brittle, while they may not be broken, a line that has hardened may not seal appropriately on the fitting it is attached to.
Has the car ever been tuned or is it still stock?
For all hoses, check to see if they are hard/brittle, while they may not be broken, a line that has hardened may not seal appropriately on the fitting it is attached to.
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Thread Starter
Launching!
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Joined: Mar 2012
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From: Milwaukee, Wisconsin
Well it's not that the RPM's are hanging, like it would be with a vacuum leak, the throttle body is getting stuck open. And while it's not physically rubbing or catching on anything, something is pressuring it to stay slightly open when I let off the gas, I have visually confirmed it in the engine bay.
I know what you're talking about and I've dealt with a vacuum issue like that where you hit the gas or rev the car and the rpms hang high and it takes a while before they drop back down, that's not what's going on this time. It's hard to explain, maybe I'll take a little video tomorrow to show what I'm talking about.
I know what you're talking about and I've dealt with a vacuum issue like that where you hit the gas or rev the car and the rpms hang high and it takes a while before they drop back down, that's not what's going on this time. It's hard to explain, maybe I'll take a little video tomorrow to show what I'm talking about.
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Launching!
iTrader: (-1)
Joined: Mar 2012
Posts: 266
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From: Milwaukee, Wisconsin
Also just to be clear the car idled high from the start, all stock but never did the hanging thing, this only started when I put the 52mm p&p stock tb on. I had this TB on my other car before this, and it did the same thing, but eventually stopped doing it so it is most definitely something with the TB or the vacuum it's causing.
