High Idle - ZR-1 Net Registry Forums

TealZR1 · 01-26-2017

Fighting a high idle around 1100 when hot. Troubleshooting now replaced PCV Valve rubber and tightened up all hoses.
Saw where an easy troubleshoot would be to change the IAC Valve on top of plenum possible problem. Is this as easy as it looks? Could it be the issue?
Thanks to all in advance.

Roadster · 01-26-2017

Quote:

Originally Posted by TealZR1

Fighting a high idle around 1100 when hot. Troubleshooting now replaced PCV Valve rubber and tightened up all hoses.
Saw where an easy troubleshoot would be to change the IAC Valve on top of plenum possible problem. Is this as easy as it looks? Could it be the issue?
Thanks to all in advance.

Just had a similar issue with my 94 after the Plenum pull last weekend. Engine would sometimes idle at 1000-1000 rpm's and then sometimes at 800 rpm's. Ended up taking out the IAC and giving it a thorough cleaning. Had a lot of carbon build up on it. Replaced and all is good. Starts and revs up to 1500-1700 rpm's and comes right back down to 700 rpm's for a perfect idle. Also cleaned inside of the opening in the plenum/throttle body area where the IAC is seated. It is as easy as it looks......

mike100 · 01-26-2017

It is probably one of the large vacuum lines under the plenum...the gas tanke purge system lines- they sometimes pop off if there is a backfire or some similar event.

msuhanek · 01-26-2017

Thanks roadster and Mike 100 for the quick reply. Those are my final two options. Will look at the IAC valve this weekend and pull the Plenum down the road if needed

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mike100 · 01-27-2017

it has been talked about before (do a search), but if you take off the air duct and block the throttle body with a stiff piece of cardboard or a phone book (anybody still have one of those?) the engine should stall. if it still runs, you can clearly locate the vacuum leak noise under the plenum.

BigIke · 01-27-2017

My hunting and high idle was caused by the large vacuum line under the upper plenum. I zip tied the hose to the plenum nipple.

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Roadster · 01-27-2017

I stand corrected, just took the 94 out for a ride, and close to the same thing on the idle. Sometimes coming to a stop idling at 1000-1100 r's. Other times around 800-900r's. So it looks like cleaning the IAC really did not have any effect on the idle, at least for me.....

secondchance · 01-27-2017

Quote:

Originally Posted by Roadster

I stand corrected, just took the 94 out for a ride, and close to the same thing on the idle. Sometimes coming to a stop idling at 1000-1100 r's. Other times around 8-900r's. So it looks like cleaning the IAC really did not have any effect on the idle, at least for me.....

Start by checking throttle body for possible binding. Also, check TPS voltage with throttle body closed.

Roadster · 01-27-2017

Quote:

Originally Posted by secondchance

Start by checking throttle body for possible binding. Also, check TPS voltage with throttle body closed.

Copy that....will do.....

lfalzarano · 01-28-2017

Or you can send it to Marc! He fixed mine.

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01-26-2017	#1
TealZR1 Join Date: Oct 2016 Location: Atlanta GA Posts: 51	High Idle Fighting a high idle around 1100 when hot. Troubleshooting now replaced PCV Valve rubber and tightened up all hoses. Saw where an easy troubleshoot would be to change the IAC Valve on top of plenum possible problem. Is this as easy as it looks? Could it be the issue? Thanks to all in advance.

01-26-2017	#3
mike100 Join Date: Feb 2011 Location: San Marcos CA Posts: 1,801	Re: High Idle It is probably one of the large vacuum lines under the plenum...the gas tanke purge system lines- they sometimes pop off if there is a backfire or some similar event.

01-26-2017	#4
msuhanek Join Date: Nov 2016 Location: Atlanta GA Posts: 13	Re: High Idle Thanks roadster and Mike 100 for the quick reply. Those are my final two options. Will look at the IAC valve this weekend and pull the Plenum down the road if needed Sent from my iPhone using ZR-1 Net Registry

01-27-2017	#5
mike100 Join Date: Feb 2011 Location: San Marcos CA Posts: 1,801	Re: High Idle it has been talked about before (do a search), but if you take off the air duct and block the throttle body with a stiff piece of cardboard or a phone book (anybody still have one of those?) the engine should stall. if it still runs, you can clearly locate the vacuum leak noise under the plenum.

01-27-2017	#6
BigIke Join Date: Aug 2014 Location: Montgomery TX Posts: 263	Re: High Idle My hunting and high idle was caused by the large vacuum line under the upper plenum. I zip tied the hose to the plenum nipple. Sent from my Nexus 6P using ZR-1 Net Registry mobile app __________________ 1991 White ZRJuan #1616 Mileage: 56K Sept-14 -- 113k May-18!!! God Damn I Love This Car!

01-27-2017	#7
Roadster Join Date: Mar 2014 Location: Warrington PA Posts: 1,914	Re: High Idle I stand corrected, just took the 94 out for a ride, and close to the same thing on the idle. Sometimes coming to a stop idling at 1000-1100 r's. Other times around 800-900r's. So it looks like cleaning the IAC really did not have any effect on the idle, at least for me..... __________________ Tom 1994 ZR-1 #009 "captured test fleet car" 1974 LS4 454 Vert 1974 L-82 355 Vert. 1982 L83 CFI...now a retired "dd"....Sold WAZOO Member Last edited by Roadster; 01-27-2017 at 02:00 PM.

01-28-2017	#10
lfalzarano Join Date: Feb 2011 Location: Clayton, North Carolina Posts: 1,133	Re: High Idle Or you can send it to Marc! He fixed mine. Sent from my iPhone using ZR-1 Net Registry __________________ Lou[COLOR="Red"][B][SIZE="4"][/SIZE][/B][/COLOR]