High idle - no vacuum leak

[cbaclawski]

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

[zrfast1]

......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.

[cbaclawski]

Originally Posted by zrfast1

......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.

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.

[secondchance]

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.

[cbaclawski]

Originally Posted by secondchance

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.

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?

[secondchance]

Originally Posted by cbaclawski

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?

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.

[Dynomite]

Originally Posted by cbaclawski

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?

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

[cbaclawski]

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)

[XfireZ51]

Originally Posted by cbaclawski

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?

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

[secondchance]

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