HELLLLLPPPPPP ME LT5 Brothers!!!

[C4Fanatic]

Drove the Z to Eureka Springs, trouble free, hasn't missed a lick. Today on a road tour the car suddenly won't idle down, wants to idle between 1500-2000 rpm. Check everything under the hood we can see, no tools, haven't pulled anything off yet. Throttle cable seems free, I hear the throttle body butterflies clicking shut , so I don't think it's failing to close all the way. Check every vacuum line we can get a hand onto. Try pinching them off to see if any change the idle speed. Nothing...no change.

Just remembered this...car is showing NO SES indication, so apparently no codes.

Tonight I'm walking up to the car from the passenger side and notice something hanging down from the fender area behind the passenger side rear tire and it appears to be trapped between the body work and the tail pipe. Reach down to grab it and find some kind of vacuum canister I believe.

Question...IS this indeed a vacuum canister that is mounted back there? Could it have come out of its mount and dropped resulting in a disconnected vacuum line? And could it possibly be causing my issue?
Any other ideas as to what may be causing my high idle speed?
I'm going to guess that to get at it, I'll have to remove the rear tire and inner fender to see it back there.

I'm headed to the tech section sticky of "Been there, Done that's" but thought I would throw this out to the experts in the mean time.

Thanks for any help in advance guys.

David

[A26B]

David,

On the passenger side of the engine, just in front of the rear pair of plenum runners, is a black plastic tube abt 1/4" dia, coming from under the plenum. Unplug the line at the connection there and put you finger over the open end of the plastic tube.

I think it's the vacuum source for the charcoal cannister that is located behind the RR wheel. If putting your finger over the now open end of the black plastic pipe restores the idle, just cap or plug the plastic pipe until you can get home to fix the cannister & loose vacuum piping or whatever is causing the vacuum leak.

[C4Fanatic]

I'll check that first thing in the morning. Thanks Jerry!

I also need to double check how the vacuum pump is acting. I read in one of the tech threads that with key on, engine off it should run for approx. 5 secs or so as it builds vacuum in the system, then shut off and stay off. If I read correctly, if it keeps cycling on and off, I am for sure to have a loss of vacuum somewhere...makes sense even to a bonehead like me...so I have a coupe directions to go.

Other than the high idle the car is running fine on the road, just make loping around town a bit of a challenge to say the least!

[gbmidyear66]

I have a similar issue, my engine has suddenly decided it wants to hang, at about the same RPM as yours. After many hours of chasing the problem, I'm convinced mine is the throttle body. One thing you might want to do is to place a STIFF book over the airhorn, see if that stalls the engine - if it does - your issue is likely not a vacuum leak (TPS, IAC, Throttle body would be next places to check).

Good luck, and let us know what you find

Glenn

[LGAFF]

IAC? Reset procedure is to start the car with pedal 3/4 depressed and then immediately turn the car off, then restart. Worth a shot

[Ccmano]

Tonight I'm walking up to the car from the passenger side and notice something hanging down from the fender area behind the passenger side rear tire and it appears to be trapped between the body work and the tail pipe. Reach down to grab it and find some kind of vacuum canister I believe.
David

I'm betting on a vacuum leak...

:happy1:
H

[C4Fanatic]

Well guys it's still not solved. Thought we had found it this morning at the car show, we found that the MAP sensor hose was indeed off...strange as it wasn't throwing a code, no SES light. Even had Gordon Killebrew climb all over the car with me today. Replaced the MAP hose and it still wants to idle between 1500 and 2000rpm. Checked every hose we could get a hand on, no luck. Disconnected power to see if we had any codes that needed cleared, still no luck. Gordon says it's acting like a vacuum leak, but we didn't find anything. Going to check a few things when I get it home, if I have time, have to fly to Vegas Monday for a week, then when I get home, it's off to Texas. I had planned to take it to Texas and go to the gathering at Cory's, but I'm just not sure right now. It runs fine on the road, so who knows, I'm still up in the air on that. Maybe someone down there will find something I've overlooked between now and then. I am going to try the IAC reset that LGAFF suggested in the morning. It's bed time.

Thanks again for all the input guys, I'll keep digging, but tomorrow it just has to get me and mama home.

[Paul Workman]

It'll be something silly, like the time a little sliver of that rubber seal they put on those circular air filters (4-bbl carburetor) somehow came off and wedged the secondary throttle plate open just a weee bit. Suddenly my idle was around 3000 rpm...SAY WHAT???

Well, I'm intrigued. Do let us know what you find!

P.

[gbrtng]

I had a charcoal canister fail - it's in the right rear fender - so you might try replacing it and check the two vacuum lines to the engine compartment very carefully.

[C4Fanatic]

I was able to climb under it yesterday and slip the canister back into the bracket it rides in and also re-attach the plastic cover that keeps debris out of that area. Both lines were on the canister and it looked fine, but I'll probably give it a closer look now that the car is home and in the garage.
Made it home with no issues today, she runs fine down the highway, but just doesn't seem quite right as far as a "seat of the pants" assessment goes, I'm sure most of you have been in that situation with your cars. She just ain't quite right.
Oh well, I'll find it, fix and be good to go again soon.

[mike100]

Mine was the purge line that goes between the purge solenoid and the throttle body. Its that hard plastic line with the 4" diameter curly-Q bend in it under the plenum (of course, where else would it be- everything is in there).

maybe backfires help those things slip out. I rough sanded mine to help keep in in the rubber connection better. It would never idle below 1400 except when cold.

the book over the throttle inlet verified this as it could still run on just the air leak. spraying some carb cleaner in the middle of the runners on the drivers side resulted in an idle speed change which verified that for me.

[C4Fanatic]

Well, just ordered a set of plenum gaskets from Jerry.
Have a trip to Chicago coming up next week, so it looks like I'll be "popping the top" here as soon as I get back home. Sounds like a good cold weather project.

I did the book over the intake trick and while the idle slowed some she kept right on running.

[C4Fanatic]

Well, I've been procrastinating and haven't torn the Skunk down yet, but the weather is supposed to be nice down here for the next couple days, so I may give it a go.

QUESTION: Where can I get new Crankcase Vent Hoses? I'd like to go with Semco, but not sure where to order them from.
Jerry got them??? I don't find them on his website.
Figured while I was under there I might want to replace them, talked to the previous owner and he said they had been brittle the last time he had the plenum off, but he didn't have replacements. I'm seeing some oil on the top of the engine between the intake runners, so I figured that was a possible source, that and a new gasket for the vent cover.

[LGAFF]

Gates - Molded Coolant Hose
Part Number: 22120

neon hose, cut it 2 makes both breathers

[C4Fanatic]

Thanks Lee!

Sorry I missed ya when I was in Chi-town earlier this month, turned out I was MUCH busier than I thought I was going to be.
I'll be back up that way in a couple weeks.


Got the hose in stock at the O'Reilly's down the street, sweeeeet!

[C4Fanatic]

OK, now I'm confused.

I was doing some basic checks before I tear this thing apart and was checking the vacuum pump...again....just in case.

I'm getting 11.4vdc to the pump, but I never hear or feel it run when I turn the key to the run position. I pulled the hose and it's not pulling anything, no suction against my thumb.

Am I doing it right? The thing should run for about 5 seconds or so when you first turn the key on, correct? I should be able to hear, or at least feel the pump run, right?

I bought a Mityvac vacuum check kit, pulled the main line out of the vacuum pump and pumped it up to 20 inches of vacuum. It took nearly 20 seconds to lose 1 inch on the gauge. Is that enough of a leak to be causing my problem?

That thumping sound is my head on my desk...

[C4Fan]

My '91 with 53,000 miles started having the same idle/running issues a few months ago right after I had the entire car serviced. While I am unable to offer any advice due to my lack of technical skills, I am anxious to hear what you finally learn about your ZR-1 C4Fanatic. I may be having the same problem and hope to narrow the field of possible cures. Thank you for sharing your experience on the net.

[sammy]

your pump is most likely either gone or the contacts inside are corroded.you can take the top off very carefully as there are wires inside . if your lucky the contacts will have that turquoise film on them .i know there is a thread on how to ck it somewhere here . do a search.or someone will chime in with the link . i dont know how to do that sorry

[C4Fanatic]

Well it's been interesting...

Did a few more checks, found that the secondary vacuum pump has died, but I'm not getting a code and that vacuum loop holds good vacuum. Seeing as the secondary's were removed by the previous owner, I'm leaving that alone for now.

In the mean time, I had to run to Chicago for business and had a chance to drop in on Mark and pick his brain. He was sure the vacuum pump wasn't causing my idle issue, totally different vacuum loop. So he pointed some things to check out when I popped the top.
Removed the plenum and NOTHING jumped out at me. Found one hose that was loose/ kinda half way off, but nothing completely off. Pushed every hose back on good and tight, zip tied any that seemed to need it. Replaced both of the crank case vent hoses as the old ones were hard as rocks. Put everything back together and crossed my fingers.
First couple times I fired it up it was still idling around 1800-2000rpms.
In a fit of madness...frustration...confusion....I shut it down and pulled the cruise control cable off. No change.
So, I pulled the throttle cable off.........SON OF A B*TCH!!! Thing fired up and idled right down to 800-900rpms just as smooth as ever.
Messed with the throttle cable, check the connection at the pedal, nothing seems wrong, it's smooth in the housing. Put it back on, fire it up...idles just fine, 800-900rpm on the tach.
SO, I don't know if it's the cable OR starting it up, shutting it off after having the battery disconnected maybe the computer was re-learning idle position. Thought???
We'll see what the next few days brings, weather is supposed to be beautiful, so I'll put some miles on it and we'll see what it does.
Keep your fingers crossed!!!

[mike100]

well, at least you know what make the top end on an LT5 tick...I guess everybody needs to dig into their car to make it their, so-to-speak.

probably the cable was jammed cockeyed or something. a scanner would have shown a high throttle position- might want to keep in mind if it happens again.

[XfireZ51]

Wait a minute! Did someone bring up the cable adjustment?? Does this car have
ASR? Never mind. False alarm. Its a 91.