High idle - no vacuum leak
 

I posted this over on corvetteforums as well, I apologize if that is not ok:

Hello,

Everyone here was so helpful last time I thought i'd try again.

1990 zr1 lingenfelter 368

I am having an issue with my idle, and it's difficult to start.

My car idles ~ 1000-1100 rpm, and when driving, say approaching/at a stop, rpm's only fall to ~2000, before eventually(usually) settling back down to the 1100 area.

Also, it doesn't start immediately upon turning the key, it has to crank for a considerable amount of time before it "catches" and fires up.

I took it to a local repair shop, and they did a smoke test and said there were no vacuum leaks. The "GM Tech" there said it was probably the coolant temp sensor, but he couldn't be sure and didn't want to experiment on my car having never worked on a zr1 before.

After reading that it could be a dirty throttle body, I did my best to clean it this morning(without removing it - just removed the intake hose, sprayed cleaner in there with the valves opened and wiped) and it did not help(if anything, it made it worse - on a test drive this morning it "stuck" ~ 3000 a few times)

For an unrelated issue, I recently replaced the injectors, plugs, and coils. The idle issue is pretty much the same as it was prior to those changes, but the "hard to start" issue started after those items.

To address this issue I replaced The idle air control valve and throttle position sensor(I did check voltages). Neither seemed to do anything.

What would you do next? (I have the new coolant temp sensor, but am reluctant to pull the plenum again to change it without a second opinion)

Thanks in advance,

Curt

Re: High idle - no vacuum leak
 

......hope you didn't clean the throttle body. The black stuff that resembles filth is actually a seal. Its called dag. Plenty of info here on that. High idle is a vacuum leak. Hope you used new seals on the injectors. Keep at it you'll find it.

Re: High idle - no vacuum leak
 

I sure did! Both unfortunately... I removed the bellows, opened the butterflies and sprayed A LOT of cleaner in there.

What can I say, I'm a genius.

Re: High idle - no vacuum leak
 

I would start with closing off the air flow at the air horn while idling with a flat piece of hard board (a book, thick plastic sheet, etc...) and see if the rpm drops. If this results in rpm drop, air leakage is at the throttle blade. If not (I hope is the case), start looking for vacuum leak elsewhere.

Re: High idle - no vacuum leak
 

I will try that today. I did have a smoke test done and they didn't find any vacuum leaks elsewhere though.


let's assume it's the throttle body for a minute, ,and that I screwed up the original by cleaning it. This one says it will fit, would it be a suitable replacement?

http://www.jcwhitney.com/bbk-power-p...&skuId=2125723

or is there another I should get instead?

Re: High idle - no vacuum leak
 

Link was bad. Are you looking for replacement throttle body? If so, I think Marc Heibeck should be able to restore your TB. There is still pretty good chance your TB is fine.
Did you connect evaporator line (black piggy tail looking hose under the plenum) correct? It tends to pop off at the bottom as you struggle to connect to the fitting under the plenum on the driver side.

Re: High idle - no vacuum leak
 

Here is the link.......that works.
http://www.jcwhitney.com/bbk-power-p...&skuId=2125723

Re: High idle - no vacuum leak
 

thanks for fixing the link. I'd rather buy a replacement than have the current one rebuilt. Mostly just because i'd rather not have the car in pieces while I wait on the round trip.

If I have both in hand, and the car drives, I can take it over to a local guy for help if I get stuck...

(yes, I definitely connected the evaporator line)

Re: High idle - no vacuum leak
 

Typical smoke test won't show leaks under the plenum. PCV is another culprit.
Doubtful JC Whitney has ANYTHING remotely related to an LT5.

Re: High idle - no vacuum leak
 

Unfortunately this is a mis-match. TB on J C Whitney is for non-LT5 vette - most likely LT1.
I looked up BBK website and they do not offer TB for LT5.
http://www.bbkperformance.com/produc...?car_motor_key[]=1503&car_motor_key[]=1514&category_key=2&left_select_reset=1

Re: High idle - no vacuum leak
 

Thanks so much for doing that.

Is there a place to buy one that will fit?

Re: High idle - no vacuum leak
 

Chances are with your 368 the DAG was long gone before you cleaned the throttle body. As it was probably enlarged to 63mm.

The other guys are correct, you are not going to find a LT5 throttle body unless its at Jerry's or on eBay, etc.

The good news is Marc will rebuild your throttle body, if indeed that is the source of the vacuum leak, and have it back to you within a couple days. I had Marc rebuild mine. I pulled it off and sent it to Marc. He had it the next day and rebuilt it, then put in back in the mail and I had it the next day. I was down for about 3 or 4 days total.

Good luck.

Re: High idle - no vacuum leak
 

Ditto for Marc.


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Re: High idle - no vacuum leak
 

That makes me feel better, thanks! I'm going to pull the plenum again and double check for leaks, get a better look at the throttle body, etc...

I've done it before, but i'm a little confused regarding draining coolant.. The other times I've pulled it I didn't do that. How/how much should I drain?

anyone have a link for the correct procedure?

Thank you guys so much for helping me!

Re: High idle - no vacuum leak
 

How much did he charge for rebuild?

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Re: High idle - no vacuum leak
 

Oh......just drain about a gallon should be plenty....if you remove radiator...drain radiator until it is empty. Then replace what you drained and fire it up :D

Have two new Plenum Gaskets on hand.

The Injector Housing Coolant Manifolds should get warm within a minute or two.

I would say Block TB Coolant at Injector Housing but I have found very few see the real advantages of that on this forum except for myself :sign10:

Same goes for Battery Disconnect and making your own oil Cooler Lines :sign10: :sign10:

Re: High idle - no vacuum leak
 

Thanks! Hopefully the gaskets good, I just had it apart 3 weeks ago!!