Stumble/Hesitation when cold
Thread Starter
Le Mans Master
Joined: Apr 2002
Posts: 5,726
Likes: 46
From: Waukesha WI
St. Jude Donor '15
Stumble/Hesitation when cold
I have a problem with my stock 90 ZF6 Vert. When cold it starts fine but it has little power, hesitates severely and will occasionally stall when I push in the clutch or just idle poorly. It is nearly impossible to get it to move from a stop w/o revving to 2K+ where I used to be able to just let out the clutch w/o adding anything from the go-pedal.
When warm it acts pretty good but there seems to be a noticable power loss and my MPG have dropped quite a bit (was 24-25 now 19-20). The computer is not throwing any codes. I pulled a few plugs (the easiest to reach) and every thing looks more/less normal.
Where do I start hunting this problem? Anything that commonly causes this problem?
Thanks all!
When warm it acts pretty good but there seems to be a noticable power loss and my MPG have dropped quite a bit (was 24-25 now 19-20). The computer is not throwing any codes. I pulled a few plugs (the easiest to reach) and every thing looks more/less normal.
Where do I start hunting this problem? Anything that commonly causes this problem?
Thanks all!
Le Mans Master
Joined: Oct 1999
Posts: 9,713
Likes: 3
From: Sachse Texas
Cruise-In I Veteran
Cruise-In II Veteran
Re: Stumble/Hesitation when cold (Professor)
It could be a couple of things. First off, is your Catalytic convertor in good shape. Mine hessitate a little when cold sometimes, but it is due to the lack of back pressure in the cold exhaust. Once the exhaust heats up, no more hessitation. I do not have cats on the car, but when I put them on for the once a year check up, it does not behave this way. If your cats or precats are clogged, you will loose power, drivability, and it will kill the car.
The other thing I would put on the top of the problem list is the IAC motor. This controls your idle quality and it is what feeds air into the motor for idle conditions. It is basically a step motor that has a pintle that moves in or out depending on how much air the system is requesting. These motors tend to get clogged with soot or simply fail. It is located on the bottom of the throttle body on the LT1's and I believe they are in the same location on the L98's. If you are having idle issues, this is the #1 item to check.
Based on your post, I would look for a clogged cat first and foremost.
The other thing I would put on the top of the problem list is the IAC motor. This controls your idle quality and it is what feeds air into the motor for idle conditions. It is basically a step motor that has a pintle that moves in or out depending on how much air the system is requesting. These motors tend to get clogged with soot or simply fail. It is located on the bottom of the throttle body on the LT1's and I believe they are in the same location on the L98's. If you are having idle issues, this is the #1 item to check.
Based on your post, I would look for a clogged cat first and foremost.
Thread Starter
Le Mans Master
Joined: Apr 2002
Posts: 5,726
Likes: 46
From: Waukesha WI
St. Jude Donor '15
Re: Stumble/Hesitation when cold (UDLUV12)
Well, I pulled the IAC out and it wasn't really dirty but I cleaned it off anyway. It did not seem to have an effect.
As far as the cat being the culprit, I have had two other cats fail on other cars and they acted nothing loke this. When those failed, the car would fall flat on its face at 2k RPM or so and could not hold highway speed.
My Vette still drives fine at speed but hesitates on throttle application. It has no throttle response. My Dad said "If it was a carb it would be similar to a 'flat spot'" if that helps any. There is still an overall power loss and MPG loss.
As far as the fuel filter, I am on my way to the store to get one right now so wish me luck.
Thanks
As far as the cat being the culprit, I have had two other cats fail on other cars and they acted nothing loke this. When those failed, the car would fall flat on its face at 2k RPM or so and could not hold highway speed.
My Vette still drives fine at speed but hesitates on throttle application. It has no throttle response. My Dad said "If it was a carb it would be similar to a 'flat spot'" if that helps any. There is still an overall power loss and MPG loss.
As far as the fuel filter, I am on my way to the store to get one right now so wish me luck.
Thanks
