Re: 92 MX-3 GS 1.8L - engine revs up and down
Posted: February 14th, 2014, 12:02 pm
The idle bounce happens when the car idles (at hot) at around 1500rpms, so then it starts surging. Check at the cause that's not the surging, but why your idle is at or above 1500. The higher your idle is, the faster it will bounce, so if it wants to idle at say 2200, it'll bound faster than if your idle would be at 1500rpms.
Turning on the A/C sends a signal to your ECU to adjust the idle because of the extra load on the motor.
My suggestions:
1) Do as the guys suggested and start with a TPS and idle screw adjustment. As a test, try to get the idle as low as you can, even if it's too low and will stall, at least it'll give you a starting point to work your way back up.
2) Try this again with the IAC unplugged.
3) If you can't get the idle low enough, look into vacuum leaks.
I had an issue with a vacuum leak that was internal to the bored out throttle body I had. I made a switch to turn the IAC on for cold starts (otherwise the idle was really low) but turned it off when she was up to temp because the idle was too high when warmed up. Having just touched your TB, it would be a leak somewhere in there, or maybe you disturbed the accordian tube for the intake, they do tend to crack with age.
Turning on the A/C sends a signal to your ECU to adjust the idle because of the extra load on the motor.
My suggestions:
1) Do as the guys suggested and start with a TPS and idle screw adjustment. As a test, try to get the idle as low as you can, even if it's too low and will stall, at least it'll give you a starting point to work your way back up.
2) Try this again with the IAC unplugged.
3) If you can't get the idle low enough, look into vacuum leaks.
I had an issue with a vacuum leak that was internal to the bored out throttle body I had. I made a switch to turn the IAC on for cold starts (otherwise the idle was really low) but turned it off when she was up to temp because the idle was too high when warmed up. Having just touched your TB, it would be a leak somewhere in there, or maybe you disturbed the accordian tube for the intake, they do tend to crack with age.