P0300 Misfire in all cylinders 2001 Tahoe

[Nicolai8775]

I got some AC Delco wires and they didn't help any. Tested everything on the intake, when I got to the IAC, I found that if I unplug it after I start the motor, there are no misfires on torque and it sounds great!

 

[Tonyrodz]

I got some AC Delco wires and they didn't help any. Tested everything on the intake, when I got to the IAC, I found that if I unplug it after I start the motor, there are no misfires on torque and it sounds great!

Might be bad. I have a bad iac on my van, which is dbc. Unfortunately they don't sell the correct iac by itself, and GM only sells the complete tb assembly, not just the iac.

 

[Nicolai8775]

Might be bad. I have a bad iac on my van, which is dbc. Unfortunately they don't sell the correct iac by itself, and GM only sells the complete tb assembly, not just the iac.

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

 

[Tonyrodz]

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

I tried there and they didn't show they even carried it in stock.

 

[Steve A]

Might be braving a trip in the 10° weather to the salvage yard to grab an assortment of IAC sensors lol. Otherwise advance Auto has one in stock for like $150

https://www.rockauto.com/en/catalog...,fuel+&+air,idle+air+control+(iac)+valve,6072

Will this one work?

 

[Nicolai8775]

Well here's the thing. It's still misfiring after I cleaned the TB and put a new IAC in. But I can still unplug the IAC right after a cold start and it will idle fine. What could be causing this?

 

[cam3439]

That I know of - if the tune was set with a vacuum leak, the tune will need to be redone. The same goes for throttle body sizes - if you adjusted the size then the tune will need to be updated to compensate.

Also, have you checked your MAF sensor? Clean the sensor with MAF sensor cleaner.

Are you able to check your fuel trims? They can be a useful tool. Like KS03 said, a leaking fuel pressure regulator can cause issues. Have you tested fuel pressure when the truck is off? Does it maintain pressure, or do you see the fuel pressure dropping?

If you unplugged the throttle body, you may need to do an idle relearn on the truck.

 

[Nicolai8775]

Well as Mike Shockey said, don't mess with the set screw. This was my first major project like this and I learned a lot lol. For some reason it wasn't clicking for me that opening the throttle by the set screw is giving it more air, but also telling the TPS it has moved and it needs more fuel etc... I thought the tiny little hole drilled into the throttle plate was good enough... Turns out I had to lower the set screw and make the hole bigger. I still need to make some adjustments because I have P0507 now, higher than expected RPM detected in IAC.

The tuner said he only saw a small leak, and the tune was "good to go" so he must not be worried about it.

I also did the scan cable tune with the stock TB on so hopefully I'm ok there. If not, I'm looking into picking up some electric fans from an 05-06 this week and I think I need a tune to make that work with the PCM anyways.

 

[Nicolai8775]

Well now I have a TPS P0122 code AND the P0507.

All I did was attempt to relearn the TPS by unplugging it after adjusting the screw down and drill a bigger hole in the blade.