Like the title says, my 3.4 has had a stutter/hesitation under a load only with the ac on. The plugs have about 25-30,000 miles on them, they are acdelco rapid fire, wires were replaced at the same time, also acdelco. Just recently had the fuel pump replaced, also a new filter. The coil packs are 2-3 years old.

When the ac is off the engine runs smooth and strong, but when the air is on at times it has a hard time getting out of it's own way...other time it runs fine.....any ideas what is wrong? 231,000 miles are on the engine.

 

Hmmm, guess not.

 

Most automobile AC systems use air doors which are controlled and operated by vacuum. May want to check for vacuum leaks when the AC is on, as the leaks could cause the engine to run poorly. A vacuum gauge connecter to the intake manifold would be helpful in trouble shooting.

 

Thanks, I'll look into that. I never even thought of that...obviously.