Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Was the sputter present before the tuneup (plugs, wires, etc.)?
Just trying to get a good history on the vehicle before attempting a diagnosis. The symptoms you describe of a misfire under load is typically due to a fault in the ignition system. This can be due to a faulty spark plug or wire, or due to a spark plug wire that was routed too closely to a hot exhaust manifold. I would check these things first. With no codes in the computer, it will be a little harder to narrow down which cylinder has the bad part, but it can still be done.
Yes, based upon the symptoms these are the most likely causes.
The area that would need to be inspected requires removal of the engine cover from inside the vehicle. Copy and paste the link below for removal instructions. Once the cover is removed, the spark plug wires will be clearly visible.
Look for spark plug wires touching exhaust manifolds. Check the ends of the plug wires to make sure they are firmly installed to spark plugs and distributor cap. Fill a spray bottle with water and a tablespoon of salt, then spray the salt water solution over the plug wires with the engine running. If there is a bad spot in one of the wires, the salt water solution will cause the wire to arc to ground. The engine will misfire and you will see the arc (spark) from the bad area of the offending plug wire.
If the wires check out okay, remove the plug wire boot from each plug and check the white porcelain area of each plug for carbon tracking (looks like black cracks on the porcelain) Replace any of the plugs that show signs of carbon tracking.
If the wires are too close to the exhaust, the insulation on the wires will break down and allow the spark plug wires to short to ground, causing a misfire. Turning the a/c off reduces the load on the engine and will reduce the tendency to misfire under load. This does still prove out the theory that you have an ignition system component causing the problem (plug, plug wire, distrubutor cap)