Coast down idle speed and idle question ..

[Vette73]

After I had the porting work done on my 91 I find it sometimes idling a little high..
At start up the car is a solid 850.....When I'm driving I notice sometimes the idle is maybe 1,000-1,100......I read the coast down idle speed is 1,200 at 20 MPH and I am right at that....I just notice sometimes it stays at 1,100 and at other times when the car comes to a stop the idle will come down to 850, maybe 775 at times but no less...

If I stab it at times it will adjust from 1,000 to 850...

The weather has been clear in the northeast ( optimum driving conditions) no humidity and good clean air so maybe it's idling at times a little high because of this?

Just figured I would put it out there because I really can't remember if my car was idling this way before the porting work...I know Hot engine idle is 650 but does it change now the car has headers, exhaust and porting work?

Don't think it is a vacuum leak because the car dies correct itself most of the time...

Car is definately more responsive with the porting work...

Anybody have these issues if you want to call it that, with there ZR-1s?

[edram454]

I have just had more extensive (siamese ported upper and injector housings) port work and my car also is idling like yours. it starts and idles at 850 or 900 but when it gets warm it stays at 1000 or 1100 which it never did before. i have notified the specialist and I am trucking it back to his shop so he can investigate. I am afraid it might be some kind of vacuum leak. It is also going for a oil leak that might be that oil light switch that go bad on these cars. I am having a hard time finding a truck to take my car. most of these companies are brokers and they put your car on a bulletin board with the price and destination so a trucker can see it and offer to two it. it is a horrible deal. I will let you know what the specialist finds.

ed ramos #3028

[Pete]

If all else is good i.e. no vacuum leaks,PCV's are sealed etc.
Sometimes overtorqueing TB screws could tweak the TB just enough to cause throttle to stick.

Pete

[Vette73]

Originally Posted by edram454

I have just had more extensive (siamese ported upper and injector housings) port work and my car also is idling like yours. it starts and idles at 850 or 900 but when it gets warm it stays at 1000 or 1100 which it never did before. i have notified the specialist and I am trucking it back to his shop so he can investigate. I am afraid it might be some kind of vacuum leak. It is also going for a oil leak that might be that oil light switch that go bad on these cars. I am having a hard time finding a truck to take my car. most of these companies are brokers and they put your car on a bulletin board with the price and destination so a trucker can see it and offer to two it. it is a horrible deal. I will let you know what the specialist finds.

ed ramos #3028

Hey thanks that would be great....Like I said it's not a major thing but it's just something I have been noticing....Car runs real strong and from what I understand the 90-92 ZR1 can take up to twenty seconds for the idle to drop when you come to a stop....

The 93-95 design from what I read only takes about four seconds to adjust...
There's something called an EPROM which they changed for those years...

Not familiar with what is called an EPROM though...

Thank you...

[Vette73]

Originally Posted by Pete

If all else is good i.e. no vacuum leaks,PCV's are sealed etc.
Sometimes overtorqueing TB screws could tweak the TB just enough to cause throttle to stick.

Pete

Hi Pete....

Car runs real strong !!!! I will check those things out....Idle does drop but sometimes gets stuck and a quick stab brings it down to 850 or so which I'm fine with...

Will check..

John...

[mike100]

If it isn't a sticky throttle or a vacuum leak (certainly probable), just be aware that even with the most updated prom from GM that addresses the high idle, these cars have the 'idle hang' during coast until you reach 4 mph or less. Lower than 4 mph and it goes to parked idle of around 750-850.

You can lower the idle targets in the chip programming, but you have to have all the air leaks addressed or it will never achieve them. if you can scan your aldl data, you want to observe the iac counts. They need to be larger than zero...if not it means the idle air stepper motor is maxed out (closed off all the way).

[XfireZ51]

Originally Posted by mike100

If it isn't a sticky throttle or a vacuum leak (certainly probable), just be aware that even with the most updated prom from GM that addresses the high idle, these cars have the 'idle hang' during coast until you reach 4 mph or less. Lower than 4 mph and it goes to parked idle of around 750-850.

You can lower the idle targets in the chip programming, but you have to have all the air leaks addressed or it will never achieve them. if you can scan your aldl data, you want to observe the iac counts. They need to be larger than zero...if not it means the idle air stepper motor is maxed out (closed off all the way).

Mike,

Very true. Another issue is if the TB has been disassembled or removed, its very likely the min air(and therefore TPS v) will require adjusting, particularly since porting "encourages" more air to come through the blades.

[Vette73]

Originally Posted by XfireZ51

Mike,

Very true. Another issue is if the TB has been disassembled or removed, its very likely the min air(and therefore TPS v) will require adjusting, particularly since porting "encourages" more air to come through the blades.

Hey thanks for the input...
Question -TPS? Throttle position sensor? I guess that's it..

Yes throttle body was removed...Like I stated I really don't think my car idled at 650 when hot before the work...I mean car was down for three months when I did all the work...

Owned car for about 8 months prior to that...I ran into another ZR1 owner this past weekend at a car show and he basically had the same work done to his...His idle he was telling me fluctuates also 850-1,000,1,100 ..

I would be happy if at all possible I can get the car between 8-900 rpm on a regular basis....

Thanks...

[XfireZ51]

Originally Posted by Vette73

Hey thanks for the input...
Question -TPS? Throttle position sensor? I guess that's it..

Yes throttle body was removed...Like I stated I really don't think my car idled at 650 when hot before the work...I mean car was down for three months when I did all the work...

Owned car for about 8 months prior to that...I ran into another ZR1 owner this past weekend at a car show and he basically had the same work done to his...His idle he was telling me fluctuates also 850-1,000,1,100 ..

I would be happy if at all possible I can get the car between 8-900 rpm on a regular basis....

Thanks...

8-900rpm should not be an issue. I have Pete's I/E cams and that's where mine idles altho its probably a bit more choppy than yours would be.
I would check the TPS voltage and see if it is not >.53 and < .58. If it isn't then the ECM thinks you aren't at idle.
Remember to check TPS v with ignition ON, but motor NOT running.
See what happens with that first.

[Vette73]

Was out with the car this morning,had to get an inspection..

Told my mechaniic about the idle issue...Seems I had the throttle cable not hooked up the proper way.....It seemed fine to me but he said just a little too much slack in it.....Idle is coming down a little better now....

Thanks for all the input...