Idle problems

[ernbuild]

Hi Guys I am having troubles with high Idle and surging at idle. Ive checked for vacumn leaks and cant find any. Any Ideas????
cheers Ernie

[ZZZZZR1]

Originally Posted by ernbuild

Hi Guys I am having troubles with high Idle and surging at idle. Ive checked for vacumn leaks and cant find any. Any Ideas????
cheers Ernie

Have you hooked your car up to a Tech 1? You can adjust your idle with that down (if it isn't a vaccum leak or problem with the throttle body).

Have you done anything to the car recently? Did you powder coat the motor?

[tccrab]

Have you done anything to the car recently?

Any changes that you've recently made that could be at the root of the problem?

TomC
"Crabs"

[ernbuild]

Have powder coated the engine, while it was apart, because it had the same problem. Found a large vacumn pipe not connected under the phelnum, and when it went back together it was pretty good ,not perfect but a lot better. Seems to have gotten worse all of a sudden.
Have not had it on a tuner as they are hard to find out here.Only know of one guy that has the right gear. Have a haibeck chip in it, will that make any difference to the tuner.??

[tccrab]

It sounds as if you still have a vacuum leak.
I'd check all your vacuum connections including the MAP sensor hose and the PCV system.
It will make no difference to the tuner if you have a stock prom or a Haibeck prom.

TomC
"Crabs"

[tomtom72]

Just tossing this out as a fwiw.....on my 90 it wasn't one or two big (detectable) vac leaks. Rather, it was a collection of really small ones from all the rubber parts in the PCV sys and the dual connector at the bottom left of the T-body....just a thought.

I used small zip ties to correct the T-body & two larger Z-ties at the PCV holder & it's top connector. I replaced both 90* el's @ the I/H's and made sure to re-tq the plenum bolts after a run cycle. I know that was a lot of redneck engineering but alot of that rubber is NLA from GM. Even the new stuff I bought when it was available didn't last long at being tight. I guess our underhood temps must kill the rubber parts quickly.



Tom

[ernbuild]

Thanks guys, have tried most of those things, plus pcv's are new as is the double rubber thing they fit into. Have also clamped every bloody hose I can get at. Wil try the tune next and check again for leaks, ???

[ZZZZZR1]

Originally Posted by ernbuild

Have powder coated the engine, while it was apart, because it had the same problem. Found a large vacumn pipe not connected under the phelnum, and when it went back together it was pretty good ,not perfect but a lot better. Seems to have gotten worse all of a sudden.
Have not had it on a tuner as they are hard to find out here.Only know of one guy that has the right gear. Have a haibeck chip in it, will that make any difference to the tuner.??

If you powder coated the throttle body and if they took apart the inside of it, that could be your problem. When my motor was powder coated, they took apart my TB and "adjusted" it. My car was running @ 2000 rpm @ idle. Using a tech 1 had no affect.... I spoke to Marc H and he said to send his TB to him and re would recalibrate it.

He did and fixed the issue! Problem is, I used a tech one to take the idle down and it did.... To where I had no idle! Had to trailer the car to a chevy station to raise the idle.

That "could" be your issue, if the shop took apart your TB.

Cheers

[tomtom72]

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.

[ernbuild]

Guys thanks for all the tech advice, but your talking to a builder here, not a mechanic, and whats worse is there are very few real mechanics out here that know anything about the LT5 motor. Its all a bit beyond me so Ill gather all this info and take it to the one bloke I know of that could help. The throttle body came off but was not powdercoated. I polished that myself , and I did know about the sealer inside. The problem only got worse recently, and I thought it may have been a poor batch of fuel, as it started to ping as well. Have a new lot of fuel now but havent had a chance to run it thru yet. Thanks again for the info, will let you know how I go.