Follow up: 1997 Galant: idle surging problem

Hi all, Its about my 97 Galant ES 95k miles with auto trans. I was experiencing idle surge with check engine light ON. The dealer extracted code P0505 Idle speed control circuit problem and conculded bad ISC motor. The motor assembly was changed two weeks back. The car was running fine, until yesterday. It started idle surge again with check engine light ON. Then it changed to rpm staying at 2000 at idle when the engine is fully warm. I will take the car tomorrow to the dealer to find out what is causing the problem. The ISC replacement had 1 year warrenty, so I am expecting a warrenty job. In the meantime, I am looking forward to you experts for any sugestions, opinions and/or comments. Thank you in advance. Morshed

The usual problems with the ISC motor are a) one of the two coils goes open circuit ie it burns out. b) the ISC internal gears chew themselves up, likely causing a).

The issue is therefore why the ISC chews up the internal gears. The usual reason is that there's a build up of carbon and fuel gum in the throttle body that stresses and jams the ISC gears. This gunk has to be cleaned out. Further, most of the carbon comes from the PCV valve that vents hot oil vapour into the intake from the rocker cover. This oil vapour can become excessive when the valve stem seals are old and not doing their job adequately any more. Since your car is a 97, its not unlikely. Piston rIng blowby is another source.

At a guess, the dealer tech has just replaced the ISC motor without doing an adequate check (and clean) of the rest of the throttle body to ensure that the ISC can adjust the speed freely. It may be that the new ISC is faulty, but its unlikely. An unexpected failure (esspesially if the ISC gears are again stripped) should result in a more detailed investigation.

Yes, its a warranty issue. Be polite to the dealer.