My idle surges from about 1k to 2k consistently but ONLY when i have the a/c on. Also, if i turn the wheel it will surge once. I think it's done it before from rolling down the window or using the sunroof too. Seems to do it when i do anything that takes any power from the engine. It used to surge all the time but when i changed the intake manifold gasket it just started doing what I stated above. Any ideas what it is? Thanks ahead of time.

 

vaccuum leak around the intake manifold? you just said it started doing it when you change the gasket, torque it down correctly.

 

nooo. I said it ONLY did it at those specific times after i changed the intake manifold gasket. Before i changed it it did it all the time. So it improved from constantly doing it to just when the a/c is on.

 

What year and engine?

 

Check for vacuum leaks first.

 

1993 Si H23 with 166k miles on it

 

Unplug the IAC and make sure base idle is between 500 and 600RPM. IF not adjust this first then plug the IAC back in and clear your code that it set. The IAC is what increases idle when a/c is on and sometimes if the idle screw is bleeding too much air it will hunt. You may still have vacuum leaks on a car of that age. All of the seals and orings on the valves that are on the throttle body are flat and brittle by now and cheap to replace. Hook a vacuum guage up to the boost valve and see if it is leaking through the diaphram.

 

Well just do like skdrcr said. Check to make sure you have vac leaks first... easiest thing. Just spray carb cleaner all around the hoses and see if you notice any change while the engine is running. Secondly, just cover the lower hole in your tb and see if there is suction... if there is, it's your fitv - which is probably the most common source for these irratic idle surges in 4th gens.

 

Remove the top cover of the Fast Idle Valve. You will see a thimble in the middle with a white ring around it. The ring gets loose and can be screwed back down . If you find, however, that your problem was with excessive bleed from the idle screw, be sure and put a dab of silicone on the head to keep it from vibrating out again. This is also a very common problem on cars that have had the factory plug removed to adjust idle.