Unusual fast idle condition

[Kevin]

marks chip is so worth it

[scottfab]

Since it sounds like you have normal idle at "open loop" time I'd start at the IAC. It's relatively easy to get of and clean.

Alternatively you could begin to isolate things at fast idle. (throttle plates sticking etc)
I take it blipping the throttle make no difference when it's at fast idle?

[Don in VT]

Hi Scott,

I had to wait for my wife while she was at Zumba class and the same thought occurred to me. I will follow the FSM instructions on trouble shooting the IAC and go from there. The IAC that is in the car is OEM and therefore 23 years old

I suppose that is could also be a ECM issue but I doubt it. I will see if I can borrow a Tech1 from work and go with it as well.

Thanks for jogging my memory.

BTW, I was born and raised in Portland, OR. Worked and retired from Tektronix. Worked part time for Northwest Investment Cars in West Slope and the old Motorsports International (Used Porsche store) located also in West Slope. I am on my 27 Vette but included in all the Vette fun was owning a Pantera, a real Cobra 427 SC and many Porsche 928's

Have a great ZR1 summer.

Don

[XfireZ51]

I think Scottfab has a good suggestion. Sticking throttle. Once motor is shut off, throttle plate returns to stop because vacuum no longer applied to it keeping it slightly open. Check out the TB.

[Don in VT]

Hi XfireZ51,

Thanks for the tip. I will do that tomorrow as well as checking and maybe cleaning the IAC valve.

Cheers,

Don

[gbmidyear66]

I had the sticking throttle plate problem (secondary) and had Marc rebuild the TB for me (works great now). I notice he adds an extra return spring during his rebuild

[XfireZ51]

Originally Posted by gbmidyear66

I had the sticking throttle plate problem (secondary) and had Marc rebuild the TB for me (works great now). I notice he adds an extra return spring during his rebuild

Yes that's what we did to mine as well. Marc said the return spring gets weaker and he adds a small one to help w the closing. Mine works fine now and frankly I like the additional resistance. There's a more direct proportional feel to the pedal.

[scottfab]

Originally Posted by gbmidyear66

I had the sticking throttle plate problem (secondary) and had Marc rebuild the TB for me (works great now). I notice he adds an extra return spring during his rebuild

Most initial failure on the TB is the plates sticking to the sides and/or top. From the factory they come with a special grease at and around the plates (some stuff used on the IAC) . People tend to over clean these. Later on as the bushings wear there is too much sloop and sticking becomes more frequent. A good way to tell is "blip" the throttle. If it slows down you got it.
Yearly cleaning is required. (or 60mo depending on use) I use axle grease on the edges of the plates (including the small idle plate in the middle at the bottom).
My personal preference is not to use an extra spring. It stiffens the peddle too much for me.

[scottfab]

Originally Posted by Don in VT

Hi Scott,
................snip
BTW, I was born and raised in Portland, OR. Worked and retired from Tektronix. Worked part time for Northwest Investment Cars in West Slope and the old Motorsports International (Used Porsche store) located also in West Slope. I am on my 27 Vette but included in all the Vette fun was owning a Pantera, a real Cobra 427 SC and many Porsche 928's

Have a great ZR1 summer.

Don

What a small world. I too worked at Tek but then who didn't back then. One of my pensions is coming from Danaher the parent of Tek. I was in the Oscilloscopes, Logic Analyzers and later Printer group for a total of 19 before moving on. Bet we know some folks in common.