After Sitting, Rough Idle.......
Thread Starter
Pro
Joined: Feb 2001
Posts: 539
Likes: 6
From: Far NW burbs of Chicago IL
After Sitting, Rough Idle.......
I did some searching and haven't come up with any help.
If my 2001 Stock C5, manual, 28K miles, may sit for several weeks....
It starts up OK, but will then idle very rough for a bit, stumbles, eventually clears up and runs well after that. This has happened several times.
I would appreciate any help.
Oh ya.........no codes..........
If my 2001 Stock C5, manual, 28K miles, may sit for several weeks....
It starts up OK, but will then idle very rough for a bit, stumbles, eventually clears up and runs well after that. This has happened several times.
I would appreciate any help.
Oh ya.........no codes..........
Last edited by ZimC6; Oct 2, 2012 at 11:56 AM.
Pro
Joined: Aug 2010
Posts: 622
Likes: 169
From: Montgomery Texas
1st - How long is a bit?
2nd - Any smoke out the tailpipe when this occurs? If so, what color?
3rd - Please confirm that the symptom does not also occur after sitting overnight. If the problem also happens overnight, are you loosing coolant? BTW - It only takes a few drops to cause this.
2nd - Any smoke out the tailpipe when this occurs? If so, what color?
3rd - Please confirm that the symptom does not also occur after sitting overnight. If the problem also happens overnight, are you loosing coolant? BTW - It only takes a few drops to cause this.
Thread Starter
Pro
Joined: Feb 2001
Posts: 539
Likes: 6
From: Far NW burbs of Chicago IL
1st - How long is a bit?
2nd - Any smoke out the tailpipe when this occurs? If so, what color?
3rd - Please confirm that the symptom does not also occur after sitting overnight. If the problem also happens overnight, are you loosing coolant? BTW - It only takes a few drops to cause this.
2nd - Any smoke out the tailpipe when this occurs? If so, what color?
3rd - Please confirm that the symptom does not also occur after sitting overnight. If the problem also happens overnight, are you loosing coolant? BTW - It only takes a few drops to cause this.
Need to get it to happen again to check for tailpipe smoke.
Doesn't happen overnight.
Didn't notice any coolant loss.
Thanks for the help guys!
Last edited by ZimC6; Oct 3, 2012 at 07:24 AM.
Melting Slicks
Joined: Jul 2012
Posts: 2,507
Likes: 9
A leaky injector will do this. When you shut the car off, the injectors should SHUT CLOSED not allowing the pressure in the fuel system to leak into the cylinders after you shut the car off. If you have a leaker, the car will be flooded on startup causing the rough idle till the car burns off the excess. That's why checking the fuel pressure (especially AFTER the car is off) will tell you if you have a leak. The pressure in the fuel rail should hold for quite some time after shutoff.
Thread Starter
Pro
Joined: Feb 2001
Posts: 539
Likes: 6
From: Far NW burbs of Chicago IL
A leaky injector will do this. When you shut the car off, the injectors should SHUT CLOSED not allowing the pressure in the fuel system to leak into the cylinders after you shut the car off. If you have a leaker, the car will be flooded on startup causing the rough idle till the car burns off the excess. That's why checking the fuel pressure (especially AFTER the car is off) will tell you if you have a leak. The pressure in the fuel rail should hold for quite some time after shutoff.
I'll check that out.
But then how do you determine which one?
Appreciate the help!
Melting Slicks
Joined: Jul 2012
Posts: 2,507
Likes: 9
Removing the plugs generally can tell you, the really black one(s) or wet one(s) are usually the culprit. Are you getting any P030X codes in the DIC when it happens?
Thread Starter
Pro
Joined: Feb 2001
Posts: 539
Likes: 6
From: Far NW burbs of Chicago IL
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Verdad Gallardo
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Joined: Aug 2010
Posts: 622
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From: Montgomery Texas
Yes, the fuel rail should maintain pressure after the engine is shut down. This is to prevent vapor lock issues on a hot restart. If the pressure drops rapidly, this would indicate a leaking injector, or a leaking check valve in the fuel pump (assuming your fuel lines are in good shape).
The best way to determine which injector: pull the injectors/fuel rail assy. out of the intake and then manually run the fuel pump for a second. The problem injector should be obvious.
*** This diag can potentially be dangerous! Do not do this with a hot engine!! Use common sense!!! If this is outside of your comfort zone, don't hesitate to take the car to a competent tech. I will not be responsible if you burn your house down!!!! ***
If all of the injectors are leak free, but the fuel pressure still drops, this would suggest the check valve, by the process of elimination.
The fuel rail should maintain pressure for several hours at a minimum. It probably will not hold pressure for days, or weeks. With no pressure in the rail, the engine will act as you describe, until the pressure builds back up and any air is forced out.
The best way to determine which injector: pull the injectors/fuel rail assy. out of the intake and then manually run the fuel pump for a second. The problem injector should be obvious.
*** This diag can potentially be dangerous! Do not do this with a hot engine!! Use common sense!!! If this is outside of your comfort zone, don't hesitate to take the car to a competent tech. I will not be responsible if you burn your house down!!!! ***
If all of the injectors are leak free, but the fuel pressure still drops, this would suggest the check valve, by the process of elimination.
The fuel rail should maintain pressure for several hours at a minimum. It probably will not hold pressure for days, or weeks. With no pressure in the rail, the engine will act as you describe, until the pressure builds back up and any air is forced out.
Thread Starter
Pro
Joined: Feb 2001
Posts: 539
Likes: 6
From: Far NW burbs of Chicago IL
Yes, the fuel rail should maintain pressure after the engine is shut down. This is to prevent vapor lock issues on a hot restart. If the pressure drops rapidly, this would indicate a leaking injector, or a leaking check valve in the fuel pump (assuming your fuel lines are in good shape).
The best way to determine which injector: pull the injectors/fuel rail assy. out of the intake and then manually run the fuel pump for a second. The problem injector should be obvious.
*** This diag can potentially be dangerous! Do not do this with a hot engine!! Use common sense!!! If this is outside of your comfort zone, don't hesitate to take the car to a competent tech. I will not be responsible if you burn your house down!!!! ***
If all of the injectors are leak free, but the fuel pressure still drops, this would suggest the check valve, by the process of elimination.
The fuel rail should maintain pressure for several hours at a minimum. It probably will not hold pressure for days, or weeks. With no pressure in the rail, the engine will act as you describe, until the pressure builds back up and any air is forced out.
The best way to determine which injector: pull the injectors/fuel rail assy. out of the intake and then manually run the fuel pump for a second. The problem injector should be obvious.
*** This diag can potentially be dangerous! Do not do this with a hot engine!! Use common sense!!! If this is outside of your comfort zone, don't hesitate to take the car to a competent tech. I will not be responsible if you burn your house down!!!! ***
If all of the injectors are leak free, but the fuel pressure still drops, this would suggest the check valve, by the process of elimination.
The fuel rail should maintain pressure for several hours at a minimum. It probably will not hold pressure for days, or weeks. With no pressure in the rail, the engine will act as you describe, until the pressure builds back up and any air is forced out.
Zim