RedRiderZR1

I have an idle issue with my 90 ZR-1. In the morning it wants to idle a 2k RPM. I cant get it to go down until the car warms up, even then I have to hit the throttle to make it drop down. Then it drops to about 1500RPM sits there for a few seconds and then drops to 800-900RPM. When it is completely warm and has been driven around the idle will fluctuate. Sometimes drops right back to where it should be other times it will want that 2k idle which I have to hit the gas to get it to drop. Anybody have any idea what the problem is.

Thanks

Bans25

I think there is a updated PROM from GM that fixes some idling problems..

also it could be the throttle plates getting sticky, or the shaft is worn causing

them to stick..

-Bill

secondchance

This is a quote from another forum. Hope this helps.

"Hi,

New to this board, but old to ZR1's. My '91 exhibited the same problem at about 18,000 miles. Problem appeared one day, and steadily got more consistent.

I learned a lot about the LT5 then, and members of other forums (and the knowledge base on this site)helped a lot, and I went thru everything, including IAC, TPI, PCV's, cruise control, new chip, removal of the plenum and re doing the vacuum. Still no fix.

I discussed it with the service manager of a local dealer, and he (contrary to my expectations) took an interest because it was a ZR1. He got the car and called GM. They sent him some software that he put on a laptop and plugged into the car while he drove it. Conclusion after a couple days and many calls to GM. An upgraded computer was needed. The original on the 91 had been there since the beginning, and this was an issue handled by later software improvements (different from the similar improvements in the "chip", which had already been upgraded). So he ordered a new computer, put my already new chip in it, and all was fine. Cost... about $200.

That was two years ago, and the car is nearing 40,000 miles now without a hiccup.

Hope this helps. It took me about 6 weeks of going thru different issues before I gave up and got the dealer involved. The problem was really devilish. After each fix, it seemed fixed... until the engine warmed up thoroughly.

Best of luck.

Regards"

RedRiderZR1

I just heard about the new CHIP that can fix this. I will take out the chip in it to see about updating.

Thanks

RedRiderZR1

Well it looks as though I may have my work cut out for me to trace this down. It puts shivers down my spine when I think about taking it to the dealer to find the problem. Can't seem to get any satisfaction when I go to the dealer, and what are my chances of getting a service manager to take the same interest as the service manager you had. Well, I will check the chip first. If that doesn't do it then I will have to try the dealer. Thanks so much for your input.

bad-zr1

Mine was similar on startup 1700 rpm then slowly drops back and pretty erratic once it warmed up. I pulled the IAC and cleaned it with carb cleaner and the idle is now 1200 at startup and drops real quick to 800 rpm. Big improvement.

:steering:

secondchance

Try rmoving and cleaning the pintle for IAC also spray 3M throttle body cleaner in the hole for IAC and use Q-tip to clean the carbon out. While you are at it, remove the accordion in front of the throttle body and use 3M spray to clean throttle plates. Small one on top is primary and 2 larger ones are secondaries. Have someone floor the gas pedal and these plates will stay open so that you can clean the back side as well. I posted earlier because I thought you have already tried this.

A26B

With engine running??? :D :D

secondchance

Well, I had my 14 yr old son sprawled on top of the motor w/ hood partially open to start spraying when he started to see the secondary open. I believe this happened in 4th gear at around 70 mph. :lol:

RedRiderZR1

I didnt know where to start looking so I posted here to get an idea on what to look for. I will take out the IAC and clean it as well as clean the throttle body plates like (Secondchance) mentioned as well. take that road first. I think it may be the throttle body plate because it idles a little high and I tap the pedal and it drops to the correct idle. Will see this weekend if that works

Thanks

secondchance

Hope that solves the problem. :thumbs:

RedRiderZR1

And I had someone ready to sit on the engine and clean the throttle body at 150mph. Just requested a couple of drinks first :lol:

secondchance

Ar'nt we a bunch of adolescent wacked out guys? God save us all! Better yet, Chevy give us more 4 cammers!!!

Hib Halverson

Forget all this talk about chips, PROMs, cleaning the IAC and so forth.

If the high idle problem can ever be fixed by simply tapping the throttle then the idle speed drops to the correct level, the first thing you need to look for is a problem with the throttle cable or a problem in the throttle body. Worn throttle body shaft bores is a problem with the LT5. If you have a TB shaft bore problem, the only shop which does the repair job right is VanDeventer Machine in Oklahoma. Contact Greg VanDeventer at 918 387 2837. He's a Mercruiser employee who did LT5 engine develoment when Mercury built the motors.