rough idle after idling several minutes

[cyhm]

So, my stock gvr4 has this odd idle issue that I haven't been able to find any info about. As the title states, it idles rough, but only after idling for a few minutes. It idles fine on start up and coming to a stop, but if it sits and idles warm for more than say 2-5min, it will begin to idle as if it has an aggressive cam grind and will progressively get lumpier until I either drive it, shut it off, or it stalls. I don't have a wideband hooked up, but oil pressure and vacuum bounce around a bit when this happens (I assume this is just because of the RPMs jumping around as well, but idk if that means anything). Aside from that, the car runs and drive fine. No noises to speak of, no odd smells or smoke, no DTCs (not that that means anything with a dsm ), no hesitation, etc. Just the strange rough idle issue. Anyone have any ideas?

I am in the process of replacing lower injector seals and tb shaft seals currently as they both were leaking slightly. is it possible for a boost/vacuum leak to cause this problem? mind you, this is not a constant idle problem. it only happens after idling for a few min first.

Update: Newly installed seals have not remedied this issue.

 

[Wurrukatte]

Quick question first...
Do you have ECMlink or an engine management system of any kind installed?

 

[sillycon]

Have you verified that your ISC is in good working order?

 

[cyhm]

No dsmlink, but it does have a socketed EPROM. The chip says stock gvr4 on it, but I'm not sure if it has any adjustments over the bone stock maps. I believe the isc is in working order, but, regardless, unplugging it has no effect on this issue.

 

[My1GLaser]

None of my DSMs seemed to idle right with a stock TB. As soon as I blocked off the FIAV they have all had a nearly perfect idle.

 

[DSM1G90]

Sounds like a vacuum leak, esp if vacuum gauge goes crazy.

Zap some WD-40 or similar around vacuum lines and see if the idle straightens out when they get zapped.

 

[TurboLaserRS]

Let me know if you figure anything out. My car does the same thing, and I have the FIAV bypassed myself, and ISC unplugged. I haven't been able to figure it out, except that the car likes to stall at exactly smack dab in the middle of the temperature gauge.

 

[cyhm]

No boost or vac leaks and my fiav is bypassed as well.

Plus, I can't imagine why a vacuum leak that serious would cause such a delayed issue. Up until the point that it idles rough, idle is near perfect.