Re: Crazy Idle
Re: Crazy Idle
Look particularly at the bottom 2 RPM ranges, in the 30-40-50 KPA areas.
What happens: When you're nearing the lean limits of your motor at idle, the RPM will slowly drop off, and KPA will increase as IAC opens. This usually gets you into a richer area in the table, which causes the RPMs to speed up (to match the opening of the IAC), so the IAC backs off. RPM returns to the original desired RPM/KPA (which is too lean), and the cycle starts over again.
Increasing timing at idle can help a motor handle leaner AFRs, and can sometimes mask this.
If you change timing, make sure you're aware that only the bottom row of the timing table gets used, no matter what your idle RPM is.
There are some other parameters related to IAC that can be changed, but it often isn't necessary. It also gets pretty complicated when you're dealing with 4-5 moving variables at the same time.