Curt Baclawski

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

1993C4LT1

Bad Idle air control valve? Not even sure if the LT5 has one. I was going to suggest dirty throttle body as well, but I see you took care of that.

Curt Baclawski

Thanks,

I already replaced the Idle air control valve... I suppose it could be faulty, but replacing it made 0 difference... If it was faulty i'd have at least expected it to change something.

Thanks again for the suggestion

1993C4LT1

Oh man, just now noticed that you mentioned that in your post. Sorry about that!

Tx_94vette

Not sure if your issue is the same my 94 is not a ZR1, but all my idle issue were caused by bad tps, to check it you can disconnect black wire on it while leaving tps plugged in, I just cut the wire and used a connecter when I was done, if it idles good then its tps probally, tps controls idle and shifting on my 94 lt1

Curt Baclawski

I have replaced the tps, and yesterday tapped the wires with a multimeter, the voltages are reading correctly, so unfortunately I don't think that's it.

I really appreciate the input 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?

FASTAZU

I realize its a lot of reading but check the sticky at the top. By Dynomite

It may help you find starting point. I don;t think you messed up the TB cleaning it maybe the gasket if you removed it, From the factory they had what is called dag (I think) to help seal the throttle plates when closed, but in your post you state it is a lingenfelter 368 so the TB may have been modified. I have also known of leaks at the plenum gasket on ported motors.

Some other great reads here.
http://www.zr1specialist.com/

I would guess a vacuum line has come lose under the plenum.

You may also want to post on the ZR1.net while a lot of the ZR-1 owners come here some do not.

mhobtr

I doubt that throttle body will work. LT5 has three butterflies, one small and two large.

Be careful cleaning the throttle body to not remove the sealer ring for the edges of the butterflies. Marc has a write up on his site about this.

When you replaced the IAC, did you clean out the inside? Carbon buildup can cause problems with the IAC seating properly.

Make sure your throttle cable is seated properly at the throttle body. Tension on the cable will hold the throttle open.

Curt Baclawski

We gone- Thanks, I did read the stickies, and have been to zr1specialist.com. You're right there is a TON of great info, but sometimes its hard to follow for a novice like me(acronyms, etc.) yours is the consensus opinion - leak under plenum - I guess I have to suck it up and check...( I have a duplicate thread over on zr1.net already - hope that's ok)

mhotbr - I did not clean out the inside, I'll def try that... Just spray in cleaner and wipe? I'll check the throttle cable too, but when I had the multimeter hooked to the tps, it was consistently smooth and reset back perfectly every time...

Looks like i'm going to have to pull the plenum again, I've done that 3-4 times now so I'm fairly comfortable doing it, but just to be sure I can't find the link with the step by step, anyone know where it is?

Lastly, the previous times I removed the plenum, I didn't drain any coolant, but now I read that I should, how and how much should I drain?

mhobtr

The best way I have found to drain the coolant is to siphon the upper reservoir until it is below the line running to plenum coolant pipe. Then disconnect the rubber hose at the plenum and connect your siphon hose to the metal pipe at the plenum. Then start your siphon and it will pull the plenum dry. I get about a gallon out this way.

Reading the TPS will not tell you if the throttle plate is closed. The TPS is adjustable independently the the plate position. Check for tension on the cable, If it slightly loose, you are OK. If it is tight, be suspicious.

I had a problem with the cable being real loose and turned out that full throttle was only 85% open. Put a smile on my face when I fixed that!