My cars RPM drops when I switch on the AC. So I need to keep pressing the acceleration pad when at rest. Its fine when I'm driving the car its alright but when I get stuck in some traffic I got to turn off the AC.

Its so hot in summer, if some one provide an useful solution it would be highly appreciated.

Its a Lancer evo VIII

  • 2
    What make and model do you have? What size engine, and are there any other problems even if they seem unrelated?
    – GdD
    Aug 5, 2016 at 8:50
  • Without any information on the car, first thing i would check is your alternator or your battery, assuming its a petrol sounds like the AC is sucking too much power to let the engine continue to run properly.
    – James T
    Aug 5, 2016 at 9:22
  • Lancer evo VIII @2009
    – Vishnu JK
    Aug 5, 2016 at 9:23
  • 1
    Does it high idle properly when the engine is cold? thinking it could be an idle control valve not properly raising the idle while the AC is on.
    – rpmerf
    Aug 5, 2016 at 10:17
  • 1
    Does the car ever stall if you come to a sudden stop? Could you get us the fuel trims?
    – Zaid
    Aug 5, 2016 at 16:09

2 Answers 2


You could have either a clogged or stuck IAC valve. Try opening the idle air screw a bit ( say one or one and a half turns ) and see if that helps.

If not, it could also be something like the bearings on the compressor seizing up.

  • The IAC is electronically controlled here. There's no screw to turn.
    – Zaid
    Aug 5, 2016 at 17:48
  • @Zaid there may be no screw to turn, but that has nothing to do with the IAC being electronically controlled. Both my current cars have electronically-controlled IAC valves and they still have idle air screws. Aug 7, 2016 at 6:26

clean throttle body most likely it is full of carbon, and removed the idle control valve clean with fuel system cleaner buy it at any parts store :)

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