Jacked up idle could be a vacuum leak.
Rump, Rump
Thread Starter
Team Owner
Joined: Mar 2012
Posts: 27,118
Likes: 135
From: Montgomery, Alabama
2017 C6 of Year Finalist
Rump, Rump
My 92 started it again. About a month ago I ran out of gas and afterwards it had a rump and rocking. It still had plenty of power and smoothed out in a couple of days.
Drove to Flips for a couple burgers on Friday and it started the rump and rocking about half way there when I goosed it to pass a slow truck. The only thing that has been done is that the alternator was replaced last Tuesday. Still has plenty of power and it smooths out when up to speed but will do it if accelerating. It is most noticeable when stopped at a red light in gear.
It is very smooth when idling but the rpm is up around 900. Prior to this it would idle in the 700-750 range.
Drove to Flips for a couple burgers on Friday and it started the rump and rocking about half way there when I goosed it to pass a slow truck. The only thing that has been done is that the alternator was replaced last Tuesday. Still has plenty of power and it smooths out when up to speed but will do it if accelerating. It is most noticeable when stopped at a red light in gear.
It is very smooth when idling but the rpm is up around 900. Prior to this it would idle in the 700-750 range.
Race Director
Joined: Apr 2003
Posts: 17,701
Likes: 1,667
From: moraga ca
My 92 started it again. About a month ago I ran out of gas and afterwards it had a rump and rocking. It still had plenty of power and smoothed out in a couple of days.
Drove to Flips for a couple burgers on Friday and it started the rump and rocking about half way there when I goosed it to pass a slow truck. The only thing that has been done is that the alternator was replaced last Tuesday. Still has plenty of power and it smooths out when up to speed but will do it if accelerating. It is most noticeable when stopped at a red light in gear.
It is very smooth when idling but the rpm is up around 900. Prior to this it would idle in the 700-750 range.
Drove to Flips for a couple burgers on Friday and it started the rump and rocking about half way there when I goosed it to pass a slow truck. The only thing that has been done is that the alternator was replaced last Tuesday. Still has plenty of power and it smooths out when up to speed but will do it if accelerating. It is most noticeable when stopped at a red light in gear.
It is very smooth when idling but the rpm is up around 900. Prior to this it would idle in the 700-750 range.
Thread Starter
Team Owner
Joined: Mar 2012
Posts: 27,118
Likes: 135
From: Montgomery, Alabama
2017 C6 of Year Finalist
Thread Starter
Team Owner
Joined: Mar 2012
Posts: 27,118
Likes: 135
From: Montgomery, Alabama
2017 C6 of Year Finalist
Would these not effect it most at higher rpms? It gets the roughest when at 900 rpm or less.
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Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Not neccessarily. The fuel pressure regulator functions off and vaccum, and the fuel pump reacts to that regulation. Last spring I had some symptoms very similar to yours. The first time was after a little highway fun, then on the side street it started sputtering. I found myself replacing the FPR and all was well. Prior to that it would do this on occasion, then "fix itself". This summer, the fuel pump finally went. On this event the car was running fine, not full of gas, but around a 1/4 tank. Sputtered, did rump, rump this time didn't come back. The fuel pressure guage test confirmed a dead pump. No troubles since. Never had any cutout at higher rpms, it was always lower range and idle that was affected. Now-a-days I look at the intermittent things that "fix themselves" as warning signs that a repair is coming down the pike.