'91 4.0L: when i start it up and it's cold outside, it idles up to about 2k RPM until it warms up then it idles normally for the most part. but if it idles for any extended amount of time, it will once and a while sound like it wants to die. it's just a real quick sputter, like a mis-fire/ back-fire almost. it's fine for the most part but once in a while it's just a real quick sputter, like when the aux fan or a/c kicks on in a car... sounds like the high idle could be a vacuum leak but would that make sense if it goes away when it warms up? what about the IAC? do you think the fuel pump could be the surging/cutting issue?
thanks
thanks