High/Hanging Idle - Page 2 - ZR-1 Net Registry Forums

lguthrie123 · 2 Weeks Ago

Check throttle plate gaps maybe, 0 IAC counts is usually for a reason. And are those really original injectors?

ssmith95 · 2 Weeks Ago

Quote:

Originally Posted by lguthrie123

Check throttle plate gaps maybe, 0 IAC counts is usually for a reason. And are those really original injectors?

I went back out to the shop and checked the throttle plates earlier and they are closed. I also pressed on them with the car running to see if they were binding and they are not.

A thick folder over the air horn still fails to stall the engine, so air is coming in from somewhere. When covered, engine rpm does drop to where it should be. I?m running out of places to look so the primary injector o-rings are looking like the next point of interest. I have pulled a vacuum on every line Ive had access to this far and they hold. I repaired two lines and they successfully hold vacuum now.

According to the prior owner, who owned the car for 22 years, only two of the injectors have been replaced. He says he ran nothing but ethanol free fuel which may have something to do with their lifespan. I?m leaning towards pulling the plenum again and removing the fuel rail to insect/replace whatever I find.

WARP TEN · 2 Weeks Ago

Out of curiosity, have you had a chance to talk with Marc Haibeck about this? If not he may have some helpful advice. Or maybe Corey since you are in Texas. Just a thought. --Bob

ssmith95 · 2 Weeks Ago

I have not, but that is a good idea. Ill send Marc an email and see if he has any insight.

ssmith95 · 2 Weeks Ago

Marc responded to my email this morning and reaffirmed that I have a large vacuum leak somewhere. In addition to his common leak locations, he suggested I check the PCV valves since incorrect valves can flow too much.

If the PCV system checks out, my curiosity will likely get the better of me this week and I'll pull the plenum again. I need to put my eyes on the primary injector o-rings and see what they look like. I really ought to just replace the stock injectors while I am in there...

I drove the car to work this morning and sitting in the garage warming up, the engine rpm was around 650 and never budged. As soon as I gave it throttle it never settled back down that low. The hunting becomes more dramatic as the engine heats up. Frustrating to say the least.

XfireZ51 · 2 Weeks Ago

Sounds too inconsistent to be a vacuum leak. Sounds to me that as soon as u stab the throttle that?s when it occurs, then quite possibly the movement of the throttle is what brings on the high idle. Throttle blade may be sticking which is what I experienced some years ago.

WARP TEN · 1 Week Ago

Quote:

Originally Posted by XfireZ51

Sounds too inconsistent to be a vacuum leak. Sounds to me that as soon as u stab the throttle that?s when it occurs, then quite possibly the movement of the throttle is what brings on the high idle. Throttle blade may be sticking which is what I experienced some years ago.

As Dominic suggested earlier, it might be partly mechanical and might benefit from the addition of the helper spring he suggested earlier in the thread. Can't hurt and it can't cost much from Marc. Maybe a combination of weak spring and a vacuum leak, unless Marc didn't think the spring would help. --Bob

ssmith95 · 1 Week Ago

Marc did not mention the spring but I'll mention it next time we talk.

I drove the car a lot yesterday and had something happen that is going to make me look at the TPS and throttle blades much closer. I pulled onto an uphill street and the car made it all the way to the top without any throttle input from me going about 30 mph. The car was very clearly accelerating and the engine rpm hung up badly when I finally pushed the clutch in at the end of the street. After 10 seconds it settled back down.

I really wish I had a datalog recording when it happened. I appreciate the input from everyone though, I have gotten tunnel vision with the vacuum leak idea and need to explore some other possibilities.

ssmith95 · 1 Week Ago

I made some headway this evening. The vacuum line on the air horn was not connected, must?ve come off when I was reinstalling the plenum. That helped to bring the idle down considerably. With that leak fixed I could hear the iac was sucking in a ton of air despite having 0 counts. I stuffed a rag in the throttle body and just covered the iac inlet. Sure enough, that brought the idle down to 650.

With that being said, other than it just being the incorrect IAC is there anything else that would cause that passage to leak?

lguthrie123 · 1 Week Ago

If there is 0 IAC counts and air is still getting through then the IAC could be a bad or wrong part, or an unseated or bad O-ring. Use TunerPro to log MAP values and track as you try different things. FSM shows a range of 20 ? 48 kPa.

If you can't determine an IAC fault it might be worth chasing down a smoke machine, there is still a lot of oddball vacuum possibilities.

Injector O-rings could be toast at this age and injectors in general could be a good investment. Any codes?

2 Weeks Ago	#11
lguthrie123 Join Date: Aug 2022 Location: DC area Posts: 4	Re: High/Hanging Idle Check throttle plate gaps maybe, 0 IAC counts is usually for a reason. And are those really original injectors?

2 Weeks Ago	#13
WARP TEN Join Date: Apr 2007 Location: Lake Bluff, IL Posts: 2,092	Re: High/Hanging Idle Out of curiosity, have you had a chance to talk with Marc Haibeck about this? If not he may have some helpful advice. Or maybe Corey since you are in Texas. Just a thought. --Bob __________________ 2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough"

2 Weeks Ago	#14
ssmith95 Join Date: Oct 2024 Location: Texas Posts: 13	Re: High/Hanging Idle I have not, but that is a good idea. Ill send Marc an email and see if he has any insight.

2 Weeks Ago	#15
ssmith95 Join Date: Oct 2024 Location: Texas Posts: 13	Re: High/Hanging Idle Marc responded to my email this morning and reaffirmed that I have a large vacuum leak somewhere. In addition to his common leak locations, he suggested I check the PCV valves since incorrect valves can flow too much. If the PCV system checks out, my curiosity will likely get the better of me this week and I'll pull the plenum again. I need to put my eyes on the primary injector o-rings and see what they look like. I really ought to just replace the stock injectors while I am in there... I drove the car to work this morning and sitting in the garage warming up, the engine rpm was around 650 and never budged. As soon as I gave it throttle it never settled back down that low. The hunting becomes more dramatic as the engine heats up. Frustrating to say the least.

2 Weeks Ago	#16
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,707	Re: High/Hanging Idle Sounds too inconsistent to be a vacuum leak. Sounds to me that as soon as u stab the throttle that?s when it occurs, then quite possibly the movement of the throttle is what brings on the high idle. Throttle blade may be sticking which is what I experienced some years ago. __________________ [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

1 Week Ago	#18
ssmith95 Join Date: Oct 2024 Location: Texas Posts: 13	Re: High/Hanging Idle Marc did not mention the spring but I'll mention it next time we talk. I drove the car a lot yesterday and had something happen that is going to make me look at the TPS and throttle blades much closer. I pulled onto an uphill street and the car made it all the way to the top without any throttle input from me going about 30 mph. The car was very clearly accelerating and the engine rpm hung up badly when I finally pushed the clutch in at the end of the street. After 10 seconds it settled back down. I really wish I had a datalog recording when it happened. I appreciate the input from everyone though, I have gotten tunnel vision with the vacuum leak idea and need to explore some other possibilities.

1 Week Ago	#19
ssmith95 Join Date: Oct 2024 Location: Texas Posts: 13	Re: High/Hanging Idle I made some headway this evening. The vacuum line on the air horn was not connected, must?ve come off when I was reinstalling the plenum. That helped to bring the idle down considerably. With that leak fixed I could hear the iac was sucking in a ton of air despite having 0 counts. I stuffed a rag in the throttle body and just covered the iac inlet. Sure enough, that brought the idle down to 650. With that being said, other than it just being the incorrect IAC is there anything else that would cause that passage to leak?

1 Week Ago	#20
lguthrie123 Join Date: Aug 2022 Location: DC area Posts: 4	Re: High/Hanging Idle If there is 0 IAC counts and air is still getting through then the IAC could be a bad or wrong part, or an unseated or bad O-ring. Use TunerPro to log MAP values and track as you try different things. FSM shows a range of 20 ? 48 kPa. If you can't determine an IAC fault it might be worth chasing down a smoke machine, there is still a lot of oddball vacuum possibilities. Injector O-rings could be toast at this age and injectors in general could be a good investment. Any codes?