I have 99 STS with 149,000 miles. No codes. My car runs great until I turn on AC. Then it starts misfiring really bad. I recently had AC charged by a trusted shop. Any
ideas what is causing my problem?
The throttlebody is the one-barrel fuel injection air intake equivalent of the old carburetor casting that contained the throttle butterflies, idle air passages and enrichment fuel bleeds.
In our cars it's the casting with a slew of cables and vacuum lines attached - the ducting from the air filter is clamped to the intake side.
To clean the thing, you use lint-free rags, a toothbrush and ........ spray throttlebody cleaner. Using a length of wood or even a golf club against the gas pedal, adjust the front driver's seat to fully open the throttle. Under the hood, remove asny rubber intake ducting at the throttlebody and push rags under the casting. You should be able to see fairly deeply into the TB bore. Judiciously (so as not to flood the intake manifold) spray, scrub, wipe the bore and throttle blade to squeaky clean. Reassemble. Make sure the intake ducting and band clamp areas are free of air leaks.
My misfire is fixed! I cleaned TB thoroughly. I replaced plugs and wires with AC Delco plugs (41-950) and Wires (748N). I'm embarrassed to say what I did to cause the misfire in the first place but I will anyway. When I changed ICM a couple of months ago, I accidently trapped a spark plug wire underneath the ICM. I bolted ICM down and pinched the heck out of the wire. I didn't notice it until today when I changed the plugs and wires. It was smashed under ICM. Live and learn I guess!