Very High Idle

[RussMcB]

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]

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.
:cheers:

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

Idle troubleshooting (http://www.zr1.net/forum/showthread.php?p=90802)
Fast idle (http://www.zr1.net/forum/showthread.php?t=11753)

[RussMcB]

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]

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]

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]

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]

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]

.... 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]

If you stab the throttle will it come back down.

[RussMcB]

If you stab the throttle will it come back down.Nope. Tried that about 20 times. :-)

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.

[Gunny]

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

removing the resonator should make a HUGE difference !!!

What size SW X-pipe? 2.5 or 3.0? or do they make a 2.75 which should have been a direct fit?

apologies for continuing off-topic conversation about exhausts ... now back on track -- be sure to double check the vac. connections at the back of the plenum. Easy to check, esp. with a flashlight and your hand ... if any of the lines are loose, it will make a big difference.

[RussMcB]

removing the resonator should make a HUGE difference !!!

What size SW X-pipe? 2.5 or 3.0? or do they make a 2.75 which should have been a direct fit?I bought their 3". I don't think they offered a 2.75".

Isn't it hard to believe Borla's resonator for the ZR-1 had such small inlets and outlets? I can only guess they must've just wanted to use something they already had on their shelves.

Thanks for the vacuum leak suggestions. I'm hoping to have time tonight to spend under the hood.

[Billy Mild]

Do you have a vacuum gauge or mityvac for testing?

[RussMcB]

Do you have a vacuum gauge or mityvac for testing?I do (both). So, is it simply building vacuum, seeing if it holds, and trying to find where it's leaking?

Tonight I only had 5 minutes to glance around in the engine bay, hoping to see an obvious problem. Everything visible seemed attached. I do have one section of very poor quality hose that needs to be replaced (attached to cruise control component, I believe).

[Billy Mild]

Hook the mityvac to the same vacuum line the vacuum pump is connected too. See if this Holds vacuum for longer than 15 minutes. Then you start pulling vacuum on the other line that are connected to the plenum.b

[Paul Workman]

Assuming the issue is an air leak, the sources to consider are:


The vacuum nipples located in the middle of the plenum; one on each side.
The plenum gasket
The IH gasket
Injector "O" rings
TB gasket
TB Idle Air Control (IAC) malfunction
TB main throttle plates ajar
Power brake booster
Fuel pressure regulator
PVC evacuation line
Evap canister evacuation line


With exception of the gaskets and "O" rings little disassembly, this should help:

1990 FSM, but later models are substantially similar:

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/plenumvacuumcircuitsLT5Large.jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/plenumvacuumcircuitsLT5Large.jpg.html)

[mike100]

I second secondchances recommendation to put a book or something that won't collapse in front of the airhorn while the engine is running. If it doesn't stall, the source of the air leak will pretty much be revealed audibly. Even though you may not see it, you can fish around with a long vacuum line stuck in your ear and the other end under the plenum until you can find the place where the air is rushing in.

[RussMcB]

Thank you. These great responses are really appreciated.

FYI - When I wired open my secondaries (and got Marc's chip), I eliminated my vacuum pump in the right front. That's what most people do, right?

[RussMcB]

Friday 6PM update...

Got home from work, ready to start working on the car and now it's idling at 900 RPM (!).

Geez. Not sure what to do now. :-)

I'll give it a test drive and see if anything changes. Maybe I'll play with Cliff's new code reader tester that arrived in the mail today...

[Paul Workman]

Ooooo! Me hates it when that happens! Nothing like the intermittent gremlin to make ya pull out yer hair (and I don't have much of mine left!).

Well, good luck.

[RussMcB]

I enjoyed having a nice low idle for a couple of minutes, but it was back high again by the first stop light.

When I got back home I did the phone book trick to stop the air going into the front snout and my idle stayed high. So, sure enough, I do have a large vacuum leak problem.

With the car running and the snout still blocked, I pulled and plugged all the easy-to-reach vacuum hoses one at a time. I could hear slight changes in RPM but none of them brought the idle down when it should be. I think that means my large leak may be under the plenum.

Today I'll repeat those tests, and try a few more things with the plenum in place, then pull it if I haven't found the leak yet.

I'm wondering if, since the idle was nice and low for a few minutes, maybe the leak is related to a source that is being controlled by the car.

Saturday afternoon update:
I blocked off the front snout, ran the car at idle, sprayed some carb cleaner under the plenum (front area) and the idle went up. So, I'm taking off the plenum now, expecting/hoping to find an obvious problem.

[8cam]

Hey Russ, did you find it? I had a similar problem that turned out to be a vacuum hose I forgot to reconnect...self-inflicted. 2k idle and would not come down. I still have a small leak somewhere, but nothing like it was. I need to pull my plenum again and run it down.

[RussMcB]

Yes, my issue was very much like yours. Tonight I'll be rerouting all vacuum lines from underneath the plenum to above (it should be relatively easy on my car since I don't need vacuum for secondaries or evap). If things go smoothly I'll take it for a test drive before bedtime to see if it's all good. Hope so, because I'm leaving Friday for Tony's C4 BBQ Gathering, and taking it to a Road Atlanta track day the next Friday. I'll probably squeeze in another trip to the dyno, to check my air/fuel ratio. Busy days.

[8cam]

Who's the track day with? And do they allow spectators? I'd love to get up there and just enjoy the day. Petit LeMans was a waterlogged mess, but I still had fun.

[RussMcB]

Who's the track day with? And do they allow spectators? I'd love to get up there and just enjoy the day. Petit LeMans was a waterlogged mess, but I still had fun.These guys: http://www.jzillatrackdays.com

I've done several events with them (mostly at AMP). Always fun. Pretty laid back. Yes, they'll allow spectators. If you're free you should come. Bring a helmet. There will be plenty of folks who'll let you ride along.

Petit LeMans was fun to watch on the web. I'll bet it was fun to be there in person, even with the soggy weather. Pretty interesting that a non-prototype won overall.

I might have fixed my high idle, but gave myself a new problem - no start. Heading back to the garage to troubleshoot that...

On edit: Yes, my high idle seems to be gone (based on my 20 second test after getting it back together). It sure sounds nice(r) when the idle is where it's supposed to be.

My problem was probably one of the large evap hard lines not staying in place.

[8cam]

These guys: http://www.jzillatrackdays.com

I've done several events with them (mostly at AMP). Always fun. Pretty laid back. Yes, they'll allow spectators. If you're free you should come. Bring a helmet. There will be plenty of folks who'll let you ride along.

Petit LeMans was fun to watch on the web. I'll bet it was fun to be there in person, even with the soggy weather. Pretty interesting that a non-prototype won overall.

I might have fixed my high idle, but gave myself a new problem - no start. Heading back to the garage to troubleshoot that...

On edit: Yes, my high idle seems to be gone (based on my 20 second test after getting it back together). It sure sounds nice(r) when the idle is where it's supposed to be.

My problem was probably one of the large evap hard lines not staying in place.

Hmmm...looks like the RA event is still open, wonder if I can get in? Been a while since I've been on track and this would be a blast. Petit was a great race and the rain was a hell of an equalizer. The GTLM Porsches were outlapping the prototypes for most of the race, really awesome to watch. We had an ezup in turn 5 so we didn't get too bad, but the mud was epic.

[8cam]

Event was still open, I'm in! Will be great to be back on the track again!

[RussMcB]

We're going to have a blast. My car ran great all weekend (trip to Tony's barbecue in Alabama). It is SO nice (low idle, lots of power, great new sound). We'll install racing brake pads, bleed 'em and we'll be all set.

And, since you were at Petit LeMans last week, you saw what we need to do to go fast there, right? :-)

[Gunny]

looking forward to hearing the new sound ... maybe a quick ride around the block, or better still, a run through the mountains