I have a 2001 z24. 5 speed. 299,000 miles, owned since new.

it developed a #3 misfire 3 weeks ago... wasnt bad, only seemed at idle but driving it was still perfect.

had ICM Tested, it passed....So i replaced spark plugs, boots, both coils, coil pack, and wiring harness for the coils.(ALL ACDELCO PARTS).... then it wouldnt start.

Finally said F it, go check ICM again, it was all of a sudden completely burnt out... so i got a new one.

Car started but no difference. Seems like a misfire atidle but some gas & it smooths out... but I hear a slight hissing like sound coming back the injectors/manifold......

and also cooling fan all of a sudden comes on &off when the car is cold and my HVAC is OFF! so wtf.

Could it be a vacuum leak , they seem good but i only know of 3 in the front of the engine...or maybe the injector is wearing out???

please help!

Move the number 3 injector and see if the problem follows to that cylinder.

Okay guys, im stumped!!!

I now moved #3 injector (where misfire is) to #4 and no change. code came right back at #3 cylinder.

I have same amount of power to all injectors so I know power is there.

-Then did a compression test. All cylinders run good at 160.

My absolute thought is o2 sensors..... they are original & it seems the plug looked like they were running a bit rich. on all 4......

I pulled the downstream one out and its very white.....

so new ACDELCO PLUGS,BOOTS,COILS,COIL HARNESS,ICM, fuel injector passes. compression is perfcct. still a cylinder 3 misfire.

please help...ive been trying for over a month..

Sorry to hear all that didnt fix it. On cold starts my 97 z would go up and down on rpm gauge and then die. Turns out one terminal was corroded and plastic had small crack. but after just cleaning them up and installing new boots and AC platinum plugs there was no more problem. Maybe in my case its still working even with small crack near terminal?

A good way to text for vacum leaks, just food for thought, is to spay carb cleaner or brake cleaner in areas that could possibly be leaking. Youll hear the engine bog down or act like its going to die, or possibly even die. Didnt know if you knew that so i figured i would throw it out there. Good luck!!


I Love My J ♡

Thanks everyone, but i ended uptaking it the dealer & the intake manifold is cracked...they wanted 800,hell no., justbought it for 300 & will be here tomorrow.

Ah yes, the good old stealership price lol. Glad to hear you resolved your issue.


2000 Cavalier Z24 5spd CRM
Eibach Anti Roll kit, Poly motor/trans mounts, custom made CAI, Header, cutout, tuned by me with HPtuners
14.81 @ 91.09 mph 2.06 60'
97 Saturn SC1 with DOHC swap. 13.7@98mph on motor. +75 shot 12.8 @107mph