So it has been running fine before changing anything, I bought a duralast Knock sensor and a wire harness, had a code for bank 2, so I replaced it and the harness, now the code is gone it keeps giving me a p0300 code for random/multiple misfires, and it won’t even start or idle without me giving it gas. Any help would be great, completely stumped

 

Just found out that I messed up the o ring on the passenger side fuel rail and is leaking a bit of fuel out, I’m going to try a new o ring and see if it’ll fix it

 

Never mind still won’t start unless I give it gas, and still misfiring

 

Did you replace both sensors or just bank 2?

Did you replace the intake manifold gasket as well and torque the bolts to spec, in sequence?

 

just bank 2, bank 1 looked fine, no rust or anything else, and yes I put a new gasket on, cleaned the mating surfaces, and I made sure to install a ACDelco one. I’ve checked almost every vacuum line and the fuel rail is not leaking. Also changed the harness for it as well, and cleaned the manifold and air filter. Not getting any other code but a p0300.

 

1) Reset the ECM adaptive memory with a battery disconnect or factory scan tool.

2) Idle engine to operating temperature while at the same time cycling the transmission through it’s gears P - MANUAL and back again, pausing for 2-3 seconds in each gear [helps warm engine and transmission].

3) Hit the highway ASAP and set the cruise at a speed you can maintain for approx. 5 miles, turn around and repeat on the drive back. 55-60 MPH ideal.

4] Use a scan tool to perform a CMP/CKP & THROTTLE BODY relearn procedure, if available. Otherwise, drive as normal until the CEL returns.

The next steps depend on if the light returns.

 

So it may have had a vacuum leak before, but there is no longer any type of vacuum leak, took it all apart again, changed bank 1 as well. Everything is correct and clean. Still giving me a misfire code, since it’s so old I’m changing the crank and cam position sensors. And I would still think it would at least idle, because it will not idle at all, I need to keep it above 800-900 rpm’s or it will stall, I’ll update in a few hours when I get back to it.

 

Remove the air filter boot.

Shine a flashlight into this bore [below] and have a helper turn the ignition to KOEO. Watch for movement of the IAC pintle & listen for noise from the IAC valve.

It may or may not move depending upon what the PCM sees from temperature sensors.




If it doesn’t move at key on, try cranking to start and see if there’s anything from the IAC valve.

If so, it’s fully functional and can be ruled out.

If not, try Tapping on the valve motor casing with the handle of a screwdriver - if it starts moving, it’s worn/corroded/etc. and needs replacing anyway.

If not, the next checks are with a test light at the connector - let me know if you need a connector pin out.

 

The IAC valve is brand new, since I had it with a warranty, and all of that is good, it’s working as it’s intended to from what I can see, there is multiple cylinders not firing when I pulled the spark plugs, I’m going to try new coil packs as well and see if that might fix it, if not then I’ll be completely lost, because I have basically all new sensors besides o2, but those are reading right on a scanner.

here’s a picture of the plugs, and these have less than 1k miles, and I gapped them to .040 thousandths and installed them maybe a month or two ago. The top is driver side, the threaded side is going into the block, so top right cyl 1 bottom right cyl 2 etc.

 

Those plugs are definitely fuel-fouled; but we know the plugs must be firing because you can keep it running, even if it won’t idle on its own.

It’s unlikely replacing the coils will resolve the problem but you can try.

Are you actually hearing/feeling it misfire or is it just recording misfires on the scan tool? If it’s just recording them, I wouldn’t spend any more time focusing on them because it’s probably a secondary problem caused by the lack-of-idling.

What does your scanner read for fuel trims? Ideally, long term and short term should be within 10% of zero at all times.