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tomtom72 · 10-14-2008

Ern,

Persuiant to what Dave just posted......if when cleaning the T/Body the "dag" was removed and/or compromised that will affect the sealing of the blades in the body's bores' and allow for an air leak to the extent that the IAC can not compensate.

"Dag" = blackish, rubbery substance forming a ring in the wall of the T/body bores to which the T/blades seat against. It allows for an air tight seal at 0% throttle.

Now I was thinking that if your idle issue is only after the motor gets hot, reaches closed loop operation? Then there might be a sensor issue, as in a 'soft' failure. O2's, TPS. IAC, MAP, IAT; back probing for voltage may reveal something in the absence of a scanner. The Emissions & Drivability Section in the FSM has diagnostic charts for voltage values. Or there could be a fuel delivery problem if the idle issue is in open loop & closed loop; including the pressure regulator (look for gas in the reg vac hose), and gas filter & pump socks & primary pump & injectors. I would also check the ing system as an outside source.

Okay, now the only other Q I have is the PROM. I'm not fluent in that stuff & I don't have a modified PROM from a tuner in my car. There was a TSB about the early 90 PROM concerning erratic hot idle issues.....only I Do Not Know if that is relavent here, sorry.

......GM issued an updated PROM to solve those issues. The TSB is over at the NetRegistry site in the maintenance section....here's the link to the TSB.
http://www.zr1netregistry.com/bulletins/476503-1.jpg

Sorry I don't have anything better to offer.

Tom

Just thought of this, and I'm not trying to be a wise guy.....did you check for oil in the MAP hose & in the nipple at the MAP? That can impair the MAP's signals to the ECM.

10-14-2008	#9
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,609	Re: Idle problems Ern, Persuiant to what Dave just posted......if when cleaning the T/Body the "dag" was removed and/or compromised that will affect the sealing of the blades in the body's bores' and allow for an air leak to the extent that the IAC can not compensate. "Dag" = blackish, rubbery substance forming a ring in the wall of the T/body bores to which the T/blades seat against. It allows for an air tight seal at 0% throttle. Now I was thinking that if your idle issue is only after the motor gets hot, reaches closed loop operation? Then there might be a sensor issue, as in a 'soft' failure. O2's, TPS. IAC, MAP, IAT; back probing for voltage may reveal something in the absence of a scanner. The Emissions & Drivability Section in the FSM has diagnostic charts for voltage values. Or there could be a fuel delivery problem if the idle issue is in open loop & closed loop; including the pressure regulator (look for gas in the reg vac hose), and gas filter & pump socks & primary pump & injectors. I would also check the ing system as an outside source. Okay, now the only other Q I have is the PROM. I'm not fluent in that stuff & I don't have a modified PROM from a tuner in my car. There was a TSB about the early 90 PROM concerning erratic hot idle issues.....only I Do Not Know if that is relavent here, sorry.......GM issued an updated PROM to solve those issues. The TSB is over at the NetRegistry site in the maintenance section....here's the link to the TSB. http://www.zr1netregistry.com/bulletins/476503-1.jpg Sorry I don't have anything better to offer. Tom Just thought of this, and I'm not trying to be a wise guy.....did you check for oil in the MAP hose & in the nipple at the MAP? That can impair the MAP's signals to the ECM. __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member Last edited by tomtom72; 10-14-2008 at 09:32 AM.