Gen 3 Prelude weird idle problem

[Filter]

My girlfriend has a 1989 Prelude Si (2.0i)

Anyway, one day it just started to idle funny, like it's revving itself up as if you drag someone .. the rpm goes from 0.8 - 1.5 rpm and back as if someone was tapping the gas and it's SOOO shame if there is someone next to you at the lights!!
When it's cold it almost stalls.

Could it be the stepper motor? whatever that is?
Perhaps the idle rate is just too low and the ECU catches it just before stalling?
Anyone else had this problem?

Cheers.

[masterofpuppets]

yeah me too on my crx........ does this sometimes after i push it a bit more... u know....... steady 140 on the highway and then after that it starts doing it..... 800-1500-800-1500. i would like to know why as well.

[funkymonkey]

the prelude problem might be u have air in your water system this happend to me in my prelude i just flushed out the radiator and after that ir went fine i have no idea how it works that way but thats what a machanic told me to do and it seemed to work so try that

[azza18]

it's a problem with the vacuum system usually, a pinhole in the vacuum hose to the map sensor will cause this problem, also it could be air in the cooling system but that's never been the cause on the variety of cars i've seen idling like that.

[cubic]

I used to get that on my DA6. It was always idling high, and sometimes would drop down and then rev back up again. I manually turned the idle speed down and it's a lot happier now. Doesn't sound quite the same as yours, as you didn't say anything about a high idle beforehand (1500rpm).