What are the causes of an irratic idle besides an intake leak? My Z idles like 1200, then to 700 when it is cold, Not like a vacume leak but more as in a rythm pattern......aaaaa mmmmm aaaa mmmm? (no wise cracks please ) once it warms up it seems to hold an idle fairly steady? It is not a vacume leak, i have a boost/vac gauge and it reads steady once it is warmed up. I have also checked for vac leaks adn nothing. I have bumped up my timing a bit but it only is worse...when it is cold?

TBI ? cleaned the IAC valve pintle off- and the hole for it in the TBI unit- and measured length of pintle to make sure its under 1 1/8" overall length- with the threads included? also take 1/2" socket and make aure the TBI unit mounting bolts are tight andf the torx-20 screws are all tight on upper TBI unit around regulator and injectors areas ?

sorry tpi unit 5.7 engine. I was thinking of the iac however, not sure? I bumped up the timing and it got worse? but it still happens when i'm at 6 deg advaced????????

Is your defrost on? Do you have AC (intact)? The defrost uses the AC compressor, and the idle RPM is increased when that is on. Otherwise, check for codes, and don't be surprised to see something with the MAF. Other than that, you got me.

With any EFI system, idle speed and quality problem diagnosis should probably always start with cleaning the TB, IAC, and checking TPS and minimum air position. A sticky PCV or failing EGR can also contribute to poor idle.

Of course, all this depends on having a sound ignition system.