Very High Idle - ZR-1 Net Registry Forums

RussMcB · 10-01-2015

I'm working through a few issues on my car, and the issue I want to tackle now is a very high idle. I'm talking 2,000 RPMs or so. Yeah, pretty high.

Should I start by determining if I have a vacuum leak? Or are there other, more likely causes I should investigate first?

What's the best way to tell if my vacuum isn't what it should be? Put a gauge on it (somewhere) and look for a specific value?

My car has wired-open secondaries, Marc's chip, and recently installed headers and aftermarket exhaust.

I've got an FSM, but haven't located a troubleshooting section for high idle yet.

Thanks for pointing me in the right direction.

Dynomite · 10-01-2015

Quote:

Originally Posted by WydGlydJim

Actually if the car is still rolling, which I think I understood, the idle is not supposed to come down under about 2000k.......only after a complete stop does the idle come down, and yes on the 90s it can take as long as 30 seconds (which seems like an eternity) for the idle to come completely down. As some have mentioned, this was an area of contention for owners, so a revised prom is the answer.

For Starters (no pun intended) I assume you are not moving in your case?

Idle troubleshooting
Fast idle

RussMcB · 10-01-2015

Thanks for the response and the question.

It stays high, even after coming to a stop.

I drove the car home (20 miles) after getting exhaust system completed (after replacing stock system with headers), and the RPM was usually around 2,000. It pretty much stayed around there, maybe dropping to 1,500 a couple of times.

It doesn't seem to change if I stop and start the engine.

I think Marc's chip probably addresses the original coast down issue. I'll probably give him a call today to get his suggestions.

secondchance · 10-01-2015

I suggest removing the air intake duct (accordion looking thing in front of the throttle body) and use a piece of thick board or a book to block the throttle body while the engine is idling and see if the RPM drops. If so, your throttle blade is not closing all the way. If high idle is not affected, I would suspect one of vacuum lines or fittings is open.

Have you removed/reinstalled fuel injectors recently? Missing injector "O" ring will do the same.

RussMcB · 10-01-2015

Great suggestion. Thank you.

Marc responded to an email. He thinks I have a very large vacuum leak, so I'll use his article to track it down.

My car has been on jack stands for 3 months, getting new exhaust, radiator and shifter. I didn't have this issue (this bad) before, so I must've introduced the problem recently, possibly with all the air pump stuff removed.

Gunny · 10-01-2015

Check your vac hose connections at the back of the plenum. Not easily seen & easily overlooked but can come loose, especially if you have a back fire during startup. Had this happen once and it played havoc with drivability until it was re-connected.

RussMcB · 10-01-2015

Thanks, Gunny.

BTW, the Borla system I bought for you is finally installed. I decided against using the cats. Sounds pretty good (I think - I had to behave during the drive home from the exhaust shop because my wife was following. :-)

Gunny · 10-01-2015

Quote:

Originally Posted by RussMcB

.... Sounds pretty good ....

I imagine it sounds very good ... I liked the sound when it was installed on my 90 - headers w/cats ... it should be a little more "aggressive" sounding w/out cats.

Are you using the Borla resonator or did you put in an x-pipe? What I had intended at one time was to swap the x-pipe for a resonator and then put a flapper on one tip each side ... couldn't figure out how to do the flappers but the FBI guys came up with the solution after I had decided to move on to the LT4 exhaust. Ah, well ...

Hope to hear your "new" exhaust in the not too distant future ... time to go to the mountains again.

Billy Mild · 10-01-2015

If you stab the throttle will it come back down.

RussMcB · 10-01-2015

Quote:

Originally Posted by Billy Mild

If you stab the throttle will it come back down.

Nope. Tried that about 20 times. :-)

Quote:

Originally Posted by Gunny

Are you using the Borla resonator or did you put in an x-pipe?

I removed the (very restrictive) Borla resonator and inserted a SW X-pipe (purchased with ZR-1 Registry discount).

I really like the flapper idea, but for me, that's for distant future consideration.

10-01-2015	#1
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,148	Very High Idle I'm working through a few issues on my car, and the issue I want to tackle now is a very high idle. I'm talking 2,000 RPMs or so. Yeah, pretty high. Should I start by determining if I have a vacuum leak? Or are there other, more likely causes I should investigate first? What's the best way to tell if my vacuum isn't what it should be? Put a gauge on it (somewhere) and look for a specific value? My car has wired-open secondaries, Marc's chip, and recently installed headers and aftermarket exhaust. I've got an FSM, but haven't located a troubleshooting section for high idle yet. Thanks for pointing me in the right direction. Last edited by RussMcB; 10-01-2015 at 01:33 AM.

10-01-2015	#3
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,148	Re: Very High Idle Thanks for the response and the question. It stays high, even after coming to a stop. I drove the car home (20 miles) after getting exhaust system completed (after replacing stock system with headers), and the RPM was usually around 2,000. It pretty much stayed around there, maybe dropping to 1,500 a couple of times. It doesn't seem to change if I stop and start the engine. I think Marc's chip probably addresses the original coast down issue. I'll probably give him a call today to get his suggestions.

10-01-2015	#4
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,717	Re: Very High Idle I suggest removing the air intake duct (accordion looking thing in front of the throttle body) and use a piece of thick board or a book to block the throttle body while the engine is idling and see if the RPM drops. If so, your throttle blade is not closing all the way. If high idle is not affected, I would suspect one of vacuum lines or fittings is open. Have you removed/reinstalled fuel injectors recently? Missing injector "O" ring will do the same.

10-01-2015	#5
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,148	Re: Very High Idle Great suggestion. Thank you. Marc responded to an email. He thinks I have a very large vacuum leak, so I'll use his article to track it down. My car has been on jack stands for 3 months, getting new exhaust, radiator and shifter. I didn't have this issue (this bad) before, so I must've introduced the problem recently, possibly with all the air pump stuff removed.

10-01-2015	#6
Gunny Join Date: May 2005 Location: Georgia Mountains Posts: 917	Re: Very High Idle Check your vac hose connections at the back of the plenum. Not easily seen & easily overlooked but can come loose, especially if you have a back fire during startup. Had this happen once and it played havoc with drivability until it was re-connected.

10-01-2015	#7
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,148	Re: Very High Idle Thanks, Gunny. BTW, the Borla system I bought for you is finally installed. I decided against using the cats. Sounds pretty good (I think - I had to behave during the drive home from the exhaust shop because my wife was following. :-)

10-01-2015	#9
Billy Mild Join Date: Aug 2014 Location: Kansas City, MO Posts: 835	Re: Very High Idle If you stab the throttle will it come back down.