Wandering idle

OK so it's pretty cold here now in ct..about 35 ish everyday and lately my riv has been idling a little weird at complete stops with the heat on it'll go from about 900 rpm then drop then shoot up to about 2000 rpm and want to die. It did die on me the other night but started right back up. I'm thinking maybe idle air control, or fuel filter maybe?? My egr ticks also I haven't gotten around to doing the egr tube gasket fix I wonder if unmetered air is causing the idle issue. Any thoughts guys?

Is your check engine light on?

Nope no check engine that's what's odd and it only does it once in a while at stop lights

When I've seen this before, primarily it's been a dirty throttle body to idle air control air passage. PCM modulates the IAC but it the passage is dirty then the air flow is wrong and your idle fluctuates.

You have to remove the throttle body to get the passage clean. Get a TB gasket from the local auto parts store that caters to GM gearheads (it won't be difficult) and a smallish aluminum baking pan like a pie plate or 1-2 lb. bread pan. Actually the dollar-store tin plated pan would be best for this - when you pull the TB, use a suitable brush and some coating-safe TB cleaner to clean the BACKSIDE of the TB. Stuff a rag into the intake and use spray TB cleaner with nozzle (and a wire or some such) to clean out the IAC air passage. Also consider replacing the IAC solenoid (you can clean and reuse it IF it is a Delphi or some such but if it is an Economy IAC you usually can't).

It might also be the idle air control is failing. They are not too pricey, less than $30. You will need "security" Torx(R) bits to R&R it, if you don't have them already (I suspect you do). If you replace the IAC, clean the TB and the air passages in the intake.

Also I notice you have a Sinister PCM and a '99 TB/MAF. I am not familiar with that setup for instance I don't know if the Sinister's fuel map is set specifically to accommodate your other mods. I imagine it would be but I don't know.

I would start by pulling and cleaning the TB and I would likely replace the IAC depending on how gummed up it seemed to be.

Vacuum leak?

AA wrote:

Vacuum leak?

At this age, unless the vac system has been overhauled then most likely it leaks, at least a little, at the rubber tees.  Last time I overhauled my vac lines the whole kit (lines and tees) was available from GM.  GMPD shows it as SKU 24508742 for about $34, "Manifold," including all the lines and tees. Listed with the Supercharger parts.  I'd think the '96 would be the same, it has the  same series engine and GM tends to use hard parts across models and years on any given platform. You MIGHT want to use some black silicone or rubber cement to seal the connections on the lines, that will buy you a little more longevity.  Don't get it in the line, just use a little around the outside of the ridge on the hose that snaps into each fitting. If you buy the factory harness don't mess with the fittings, they are already secured IIRC.

A big vac leak (cracked or disconnected line) can cause a rough idle. This has happened on my car a couple times before replacing the lines.