90 ZR-1 -rough idle and knock

[1971 Judge]

Gents, Need your input here.

34k mile ZR-1. Always maintained.

Upon start up, she's' rough on idle and knocks loud and bad. No smoke, no odors...just sounds horrible and pretty much won't drive.

Injectors...?

Advice...? TIA.


Here's the video: https://youtu.be/4pMqqsoofvE

[secondchance]

First, I would check MAP sensor vacuum hose. MAP sensor is under 1-1/? X 3-4? wide aluminum cover right behind the center of the plenum. Rubber fitting at both ends and a hard plastic hose - connects to a nipple on the back of the plenum low. Back fire can blow the hose off resulting in incorrect data to ECM.

[1971 Judge]

Thanks for the reply, do appreciate it, but it's not the MAP sensor - it's good.

I think it's the IAC. Funny - I'm not 100% sure of its location on the throttle body - been looking on Google images just to make sure, but no luck yet.

[secondchance]

Originally Posted by 1971 Judge

Thanks for the reply, do appreciate it, but it's not the MAP sensor - it's good.

I think it's the IAC. Funny - I'm not 100% sure of its location on the throttle body - been looking on Google images just to make sure, but no luck yet.

IAC is on the passenger side, on the throttle body. Held in with two tore screws.

[1971 Judge]

Good news - replaced the IAC valve, we're back and good as new.

[1971 Judge]

Originally Posted by secondchance

IAC is on the passenger side, on the throttle body. Held in with two tore screws.

Thanks Buddy! Got it

[Erik]

Originally Posted by 1971 Judge

Good news - replaced the IAC valve, we're back and good as new.

That's is excellent news. May it always go so well.

[wfot]

I have found GM parts for the electronics to be the best replacements. The GM stuff is what the ECU makes all of its calculations from and aftermarket parts fit in a "window" of tolerance and sometimes are outside the window GM part/ECU needs to see.

Also get the voltage reading on the IAC .053 - 054 volts when the ignition on and 0% throttle..... if you haven't already done so.. this is the accepted best voltage reading for all around performance..

John

[Ccmano]

Originally Posted by wfot

Also get the voltage reading on the IAC .053 - 054 volts when the ignition on and 0% throttle..... if you haven't already done so.. this is the accepted best voltage reading for all around performance..

John

Sorry John, but that's incorrect. IAC, on the passenger side, is the idle air control unit. There is no adjustment to it other than a specific sequence for turning the engine off and on after installation.



The throttle position sensor, on the driver side of the plenum requires the adjustment to 0.54 volts, giving the ECM a base throttle voltage at 0% throttle.
H

[wfot]

Holy Crap,
yes I was thinking of the TPS, my mistake. please forgive.

John