Fast Idle

Vettn71 · May 20, 2014

Just had my a/c repaired (everything but the evaporator). Before this the car I idled at a steady 650 rpm, but afterwards it idles at 800, but stays at 1,000 rpm for a while. Thought it might be a vacuum leak, but don't see anything. Really seems odd. Could use some thoughts on this

TIA

Jim

MikeBo · May 26, 2014

Don't know if this helps, but my car idles at 800, maybe 650 was low?

94mustangsvt · Jun 3, 2014

Around 700 rpm is typical for a stock idle. Try cleaning out your IAC valve with MAF sensor cleaner. They get dirty with age and can cause idle surging and sticking issues.

toyman · Jun 3, 2014

ECU idle command for the manual is about 650 and the auto is 700 +/- 10 rpm. Vacuum leaks can be very difficult to spot and locate. The only sure way is to have a smoke test. The IAC cannot be cleaned other than cleaning the protective bellows surrounding the solenoid valve. The IAC is an open or closed solenoid valve. If it's the original it may be failing or not responding like it should to maintain the idle.

94mustangsvt · Jun 3, 2014

toyman said:
ECU idle command for the manual is about 650 and the auto is 700 +/- 10 rpm. Vacuum leaks can be very difficult to spot and locate. The only sure way is to have a smoke test. The IAC cannot be cleaned other than cleaning the protective bellows surrounding the solenoid valve. The IAC is an open or closed solenoid valve. If it's the original it may be failing or not responding like it should to maintain the idle.

What year is your Mustang? I've pulled off the IAC valve, cleaned it out, and saw immediately improvement on about five different 94-95 5.0s so I beg to differ.

toyman · Jun 4, 2014

94mustangsvt said:
What year is your Mustang? I've pulled off the IAC valve, cleaned it out, and saw immediately improvement on about five different 94-95 5.0s so I beg to differ.

'94 GT. As I said you can only clean the bellows protecting the solenoid valve and seat. Now, that's not to say there might be a lot of crud in the air passage and on the bellows which may affect air flow and the movement of the valve. However, you cannot clean the valve and the seat. So, if the valve is not seating properly or the electronics are not responding properly no amount of cleaning is going to help.