Scotty,My 2003 Corolla has me confused.I've had it for 3 years.I've driven it from 102,000 miles to 140,000 miles.Shortly after I got it I installed Denso Iridium plugs,Replaced the PCV valve,cleaned the throttle body,replaced the throttle position sensor,replaced the upstream O2 sensor,replaced all four coil on plug units ( two are Denso,two are Duralast.The car runs great,shifts great,but it glitches sometimes.The glitching started happening around the time I slightly raised the idle speed ( raised about 100 rpm) using the throttle stop screw.The glitch is that at random times the engine will stumble ( like a giant hand grabbed the serpentine belt and tried to stop the engine) and it normally happens at a stop sign or red light.The glitch is over in a split second ( about as fast as you can say "whoa").I used the stop screw to lower the idle back to where I believe it used to be ( using the instrument panel tach,about 550-570 rpm).It then had the same glitch but instead of at red lights I felt it several times right after pressing the accelerator pedal.I felt it a couple times under light acceleration and at cruise with a steady throttle.The glitch seems to be occuring more frequently now.When it isn't glitching it is running fantastic.I'm wanting to drive the car from Ohio to New York City next week.I'm slightly concerned about the glitching.I just switched to BP gas because A young guy at Shell,where I was going,made me mad.It seems like,possibly,switching gasoline brands made the glitch appear at different times than before.I'm kind of leaning towards a defective throttle position sensor,coil on plug going bad,or maybe needing a new idle speed control valve ( if thats what Toyota call it?) Any thoughts?Thank you for all your efforts to help people!-Dave W.

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NEVER mess with that stop screw, it is NOT for setting idle speed. You now messed with the tps sensor and other measurements to the computer. It has to be at factory setting, then you might just try this cleaning video to fix the glitch