I have a 1998 buick lesabre with a 3.8. When I start the car it runs ruff for a minute or two than smooths out. It is not kicking out any codes and my mechanic has no idea what it could be. It doesn't always do it but does more often than not.

First: Run from that "mechanic". Maybe run quickly. If your "mechanic" has no idea then yeah run.

Likely a flaky injector, might be a coil pack going bad, maybe old spark plugs, maybe bad wires. Maybe bad fuel pump, or plugged fuel filter. Could be low compression on a cylinder.

How many miles on this car?

How many miles have you owned it?

How many miles on the spark plugs?

How many miles on the wires?

What region does it live in?

Me thinks IAC isn't opening all the way. Usually due to carbon build up.

The car has about 98,000 miles on it. I bought it with 58,000. It has new plugs. I am not sure about the wires. I live in SW.GA I just had the plastic intake manifold replaced because it cracked. I just got back from a 2000 mile trip the car ran great but did cut off a couple of times but started right back up. Again no code or check engine light came on.

Can you please tell me what the IAC is?

Give this a read....

https://www.gmforum.com/normal-maint...800-v6-307092/

I would replace the wires if they are old. The plugs require higher voltage when the engine is cold and if the wires are getting resistive it'll cause poor ignition.