Rough idle/stutter at low RPMs
Thread Starter
Pro
Joined: Apr 2005
Posts: 603
Likes: 2
From: Illinois, USA
Rough idle/stutter at low RPMs
I've just started to pick up a problem with the vette in the last couple weeks were the idle is a bit rough (has the V8 shake) and when power is applied at low RPMs (heavier accelleration in 4th gear with RPMS < 2k for example), you can definitely feel it be uneven.
Sounds to me like a classic miss problem. I did find a plug boot that was "soft" from heat from the exhaust manifold. I replaced it and created a make-shift aluminum protector for it -- the symptom didn't change.
Car acellerates just fine and maintains higher RPMs with no noticable problem -- including WOT.
The engine is a L48 with Q-jet. New plug wires, plugs, rotor and dist cap. Timing is solid and to spec (8 deg BTDC w/no advance).
Anyone have an experience similar to this, and what did you find?
Thanks a bunch,
Brian.
Sounds to me like a classic miss problem. I did find a plug boot that was "soft" from heat from the exhaust manifold. I replaced it and created a make-shift aluminum protector for it -- the symptom didn't change.
Car acellerates just fine and maintains higher RPMs with no noticable problem -- including WOT.
The engine is a L48 with Q-jet. New plug wires, plugs, rotor and dist cap. Timing is solid and to spec (8 deg BTDC w/no advance).
Anyone have an experience similar to this, and what did you find?
Thanks a bunch,
Brian.
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
Just for kicks you might disconnect the main vacuum lines from your intake manifold (between the carb and distributor) and plug it off. You could probably even just start the car with the two (usually) hoses disconnected, and then put your fingers over the nipples to see if it smooths out. If the idle smooths out-- you probably have a vacuum leak somewhere. If not-- well it was something easy to eliminate...
Thread Starter
Pro
Joined: Apr 2005
Posts: 603
Likes: 2
From: Illinois, USA
Originally Posted by Driftwood
Just for kicks you might disconnect the main vacuum lines from your intake manifold (between the carb and distributor) and plug it off. You could probably even just start the car with the two (usually) hoses disconnected, and then put your fingers over the nipples to see if it smooths out. If the idle smooths out-- you probably have a vacuum leak somewhere. If not-- well it was something easy to eliminate...
Brian.
Racer
Joined: Aug 2002
Posts: 289
Likes: 0
From: Albuquerque NM
When checking for a VAC leak a good trick is to take a Propane Torch (not Lit) and run it around the suspect areas and listen for a change in Idle. This is very easy and will nail down the area with the leak.
Larry
Larry
Thread Starter
Pro
Joined: Apr 2005
Posts: 603
Likes: 2
From: Illinois, USA
Problem found w/Pics
I think I found my issue. I guess I had suspected that I was down a cylinder, as it felt like that kind of miss -- and I think I found the smoking gun, as it were:
I found the boot of that plug wire had melted, so it might have not been firing that cylinder for a bit. I replaced the wire and put in all new AC Delco plugs. In the process, I found another one that was heat damaged on the other side of the block, and replaced that wire as well. I also installed some protective tubes over the boot and wire to protected it from the high manifold heat. I rechecked the fast/curb idles and adjusted them a bit.
On the upside, I now have a few more tricks for tracking down vacuum leaks
Thanks for all your help guys.
Bonus pic:
Brian.
I found the boot of that plug wire had melted, so it might have not been firing that cylinder for a bit. I replaced the wire and put in all new AC Delco plugs. In the process, I found another one that was heat damaged on the other side of the block, and replaced that wire as well. I also installed some protective tubes over the boot and wire to protected it from the high manifold heat. I rechecked the fast/curb idles and adjusted them a bit.
On the upside, I now have a few more tricks for tracking down vacuum leaks
Thanks for all your help guys.
Bonus pic:
Brian.
