Hunting idle issue - ZR-1 Net Registry Forums

MuRCieLaGo · 11-10-2017

Hello guys,

Today is a good day. Been searching for a long time for my low RPM bucking issues (especially when warm).

Changed o2 sensors, fuel filter, fuel pumps, spark plugs, spark plug wires, cam sensor, battery... All without success.

Today, I changed the coil packs. It seems to have fixed the problem. The car was running fine at high RPM, I still don't understand!

Anyway, it brought a new problem. I've got slightly high and hunting idle now. As you can see in the video, nobody touched the gas pedal on throttle cable and it went all the way from 800 RPM to 1,900 RPM all of a sudden.

https://www.youtube.com/watch?v=Jr7QD11eJzs

I've got no clue what it could be.

Any ideas?

Thanks!

Ccmano · 11-10-2017

A hunting idle is almost always a vacuum leak. No magic bullet for that. Just a matter of going through and checking and eliminating the various vacuum systems.
H

Billy Mild · 11-10-2017

Vacuum leak. Make sure everything is ZIPtied or RTV'd to seal up any leaks. Outside of that if that all checks out then place a book in front of the airhorn. If the idle drops down then that is your issue. The TB sticks.

On the point of getting the Vacuum leaks fixed make sure to use a mityvac on each connection with the manifold on to see where its leaking at. The MityVac really helps pinpoint this stuff.

GOLDCYLON · 11-10-2017

Vacuum leak X3

XfireZ51 · 11-10-2017

When you swapped coil packs, did you disconnect throttle cable when removing plenum?

MuRCieLaGo · 11-10-2017

Vaccuum leak - I'll double check...

But personally I think XfireZ51 is closer to finding the problem.

When I disconnected both cables, I heard a weird sound from the system - like if I broke something... Couldn't see anything obvious though.

In the video, you can see that it went from 800 RPM to 1,900 RPM pretty fast. A raise to RPM due to vaccuum leak would be much slower, no?

By the way, thanks a lot for your help guys. I bought a Viper 1994 and the forums are pretty bad. People are being sarcastic and think they own a Ferrari. I love this forum here.

MuRCieLaGo · 11-10-2017

I just started it at a pretty cold weather and I had a rock solid idle at 1,500RPM...

Ccmano · 11-10-2017

What year is the car?
H

MuRCieLaGo · 11-10-2017

1991

Ccmano · 11-10-2017

So we can count out the ASR adjuster cable, 90’s and 91’s didn’t have ASR. Check the throttle and cruise control cables, there should not be any tension on them at idle. Just a very small (tiny) amount of slack.

Make sure there is nothing interfering with the throttle linkage assembly to hold it slightly open. That assembly where the throttle cables hook into.

If you find that the throttle linkage is fully at rest when idling we have to look elsewhere.

The IAC motor is another possibility. It was no doubt disconnected when the plenum was off. Try resetting it. #4 post in the following thread.
http://www.zr1.net/forum/showthread....ight=IAC+reset

I still strongly suspect a vacuum leak somewhere.
H

11-10-2017	#1
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Hunting idle issue Hello guys, Today is a good day. Been searching for a long time for my low RPM bucking issues (especially when warm). Changed o2 sensors, fuel filter, fuel pumps, spark plugs, spark plug wires, cam sensor, battery... All without success. Today, I changed the coil packs. It seems to have fixed the problem. The car was running fine at high RPM, I still don't understand! Anyway, it brought a new problem. I've got slightly high and hunting idle now. As you can see in the video, nobody touched the gas pedal on throttle cable and it went all the way from 800 RPM to 1,900 RPM all of a sudden. https://www.youtube.com/watch?v=Jr7QD11eJzs I've got no clue what it could be. Any ideas? Thanks! Last edited by MuRCieLaGo; 11-11-2017 at 06:19 PM.

11-10-2017	#2
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Hunting idle issue A hunting idle is almost always a vacuum leak. No magic bullet for that. Just a matter of going through and checking and eliminating the various vacuum systems. H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.

11-10-2017	#3
Billy Mild Join Date: Aug 2014 Location: Kansas City, MO Posts: 838	Re: Hunting idle issue Vacuum leak. Make sure everything is ZIPtied or RTV'd to seal up any leaks. Outside of that if that all checks out then place a book in front of the airhorn. If the idle drops down then that is your issue. The TB sticks. On the point of getting the Vacuum leaks fixed make sure to use a mityvac on each connection with the manifold on to see where its leaking at. The MityVac really helps pinpoint this stuff. __________________ Looking for a ZR-1 1985 Yamaha RZ350-NOT STOCK 1971 Yamaha AT1-Middle of a restoration

11-10-2017	#5
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,707	Re: Hunting idle issue When you swapped coil packs, did you disconnect throttle cable when removing plenum? __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

11-10-2017	#6
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: Hunting idle issue Vaccuum leak - I'll double check... But personally I think XfireZ51 is closer to finding the problem. When I disconnected both cables, I heard a weird sound from the system - like if I broke something... Couldn't see anything obvious though. In the video, you can see that it went from 800 RPM to 1,900 RPM pretty fast. A raise to RPM due to vaccuum leak would be much slower, no? By the way, thanks a lot for your help guys. I bought a Viper 1994 and the forums are pretty bad. People are being sarcastic and think they own a Ferrari. I love this forum here.

11-10-2017	#4
GOLDCYLON Join Date: May 2007 Location: Peoria, AZ Posts: 9,155	Re: Hunting idle issue Vacuum leak X3 __________________ GOLDCYLON - 91 ZR-1 #2014 GOLDCYLON - 90 ZR-1 #2794, 4L60e (Formerly Schrade's) GOLDCYLON - 11 CTS-V Arizona State Director 91 WHITE/BLACK #2014. 380 P&P&PCed,Ported Heads, Jeal Long tubes, Corsa Exhaust/FIKSE FM-5s /LED TLs, LED Headlights, Front Wilwood 6 piston narrowlite calipers and rear Wilwood caliper street shop mod,CNCed Coolant Pipes,TPI Cvr,Filter cover,Stainless Bolts, DRM/DOM PROM /ZFDOC mod build #102,DRLs,BMAD with stainless Debris Screen,Coplan Air Blaster, Pioneer APP Radio 4,Brey-Krause HB,Sub Bar,Fire extinguisher seat mount,DRM Coilovers,LEDs everywhere,Compass mirror (orange),V1 DIC hidden display, Homelink sun visor, Carbon Fiber top x3 and APSIS Carbon Fiber interior, APSIS CF Steering Wheel/NAPA Leather, Banski trailing arms, Guldstrand front suspension,urethane bushings from Prothane (total suspension) ZFDoc drive shaft safety loop, raptor shift light (orange),AO engineering louver front plate, Console seat cushion, 96CE seats with black custom Sheepskins, ss billet catch can,Viper remote entry/alarm,Cragar Rear Louvers,LED side louver lights, Dewitts Radiator with SPAL fans and a Woods 160 T-Stat 90 RED/BLACK #2794. 4L60e Automatic Stage V by RPM Transmission, TCI Dedicated TCM, OBX Stainless Headers, Corsa Exhaust, SAN Secondaries and Haibeck PROM, Exotic Muscle Coil overs, LED Interior Lights, LED Tail Lights, LED Headlights, 94 Sport seats with black custom Sheepskins , Cragar rear louvers, GS Front calipers, Banski Trailing arms, APSIS Carbon Fiber steering wheel, Front and Rear Baer Eradispeeds, DRLs, Guldstrand front suspension,urethane bushings from Prothane (total suspension), Dewitt's Raditor with Dual SPAL fans and a Haibeck 170 T-Stat 11 RED/GREY CTS-V

11-10-2017	#7
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: Hunting idle issue I just started it at a pretty cold weather and I had a rock solid idle at 1,500RPM...

11-10-2017	#8
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Hunting idle issue What year is the car? H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.

11-10-2017	#9
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: Hunting idle issue 1991

11-10-2017	#10
Ccmano Join Date: Jun 2006 Location: Sparks, NV Posts: 2,852	Re: Hunting idle issue So we can count out the ASR adjuster cable, 90’s and 91’s didn’t have ASR. Check the throttle and cruise control cables, there should not be any tension on them at idle. Just a very small (tiny) amount of slack. Make sure there is nothing interfering with the throttle linkage assembly to hold it slightly open. That assembly where the throttle cables hook into. If you find that the throttle linkage is fully at rest when idling we have to look elsewhere. The IAC motor is another possibility. It was no doubt disconnected when the plenum was off. Try resetting it. #4 post in the following thread. http://www.zr1.net/forum/showthread....ight=IAC+reset I still strongly suspect a vacuum leak somewhere. H __________________ 90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold.