Expert: Vern Bullock - 7/3/2008

Question
QUESTION: I recently rebuilt the engine (original 350 with only 400 miles on it so far), in my '75 Nova. It was running fine with no problems until about 2 weeks ago. I started it up pulled out into the street drove about a mile, and suddenly it felt like it was trying to stall out on me when I let all the way off the gas, when coming to a stop. It runs smooth when accelerating or cruising. What could cause this?
Thanks!

ANSWER: If it idles rough, but appears to drive OK at high speed, I would look into two areas for the cause...

1. If it happens all the time, you would have air leaks in the intake causing the air/fuel mixture to be incorrect. However, if this is the case, you should notice the car running richer or even hotter exhaust, as unburned fuel enters the exhaust manifold.

2. I've also seem this happen with a stuck/sticky automatic choke. Check the choke linkage to make sure it's not pushing too much fuel to the carb.

Its also a goo idea to check the spark plug wires. One make have just off or is loose and arcing. This could also give you a rough idle.

Hope this helps. These are the easiest to check. I'm guessing one of them will be your problem. If not let me know.

---------- FOLLOW-UP ----------

QUESTION: Ok, adjusted the choke. Checked plug wires. Now it's different. The car has been idling fine when at a complete stop. But it still runs rough when slowing down to a stop. If it was an air leak in the intake, how could I check for one?
Thanks!

Answer
Check the air filter on the carb to make sure it is new and clean. Also you can check to make sure there is no air leaks around the the intake manifold or any of the hose leading to the carb.

Also, if you haven't change the plugs in awhile, they may be fouled. So changing the plugs may be required.