Originally Posted By: buster
Originally Posted By: eljefino
I bet it's a heat soak/ knock retard situation. Try some high-test?
My saturn with CCOT compressor does this in spades. Until it partially cuts out due to over cooling it takes twice the torque per second at half the RPM. So idling speeds really drag the car down.
I put super in and it made a huge difference. Why though? I thought using regular/plus made no difference? I filled up at Citgo this time instead of Shell. I'm really surprised using a higher grade gas made such a difference!
High ambient temps combined with heat from the A/C system can really work an engine. High intake temperatures as well, even if coolant temps are normal, can contribute to preignition, especially if there's any carbon buildup in the cylinders. When that preignition occurs from the load on the engine from the A/C compressor turning on, the knock sensor will pick it up and retard the ignition timing. That is likely what you're feeling.
I've had many cars that do this and premium fuel does help a lot, and even with trying fuel system cleaners and such to get the engine clean to reduce detonation, I've found in extreme heat, the car just never is the same as when it was new. Could be from 150,000 miles of junk clogging the radiator/condenser and reducing airflow creating heat soak.
You could try a few rounds of fuel system cleaning. I recommend Redline SI-1 or Techron. See if that allows you to run mid regular unleaded. Might want to take a gander at the front of the A/C condensor or remove the shroud from the radiator and see what kind of gunk is sitting on the face of the radiator.
After this tank of premium fuel is used up, try regular again, and with the A/C on, roll your windows down and see if you can hear any knocking from the engine when you're accelerating. that will tell you it's detonation/preignition that is causing the power loss.
