5.3 backfire and rough idle

[myzterray]

just finished a 5.3 swap into my 96 tahoe. starts right up but it idles really high sometimes and sometimes it idles fine. when i give it gas i get a loud pop comin for the header. right now it open headers no air intake and no o2 sensors plugged in yet. also i was told i need the coolant temp sensor from the 5.3. i removed it and just running the adapter for my dash with the 96 sensor. any ideas fellas?

[bstill]

Put your O2s in and put exhaust on it. It probably doesn't know what's going on without the rear O2s. You're going to need exhaust because when at idle there isn't much exhaust flow and fresh air will get to the O2s causing it to run rich, which will cause a rough idle.

[myzterray]

Put your O2s in and put exhaust on it. It probably doesn't know what's going on without the rear O2s. You're going to need exhaust because when at idle there isn't much exhaust flow and fresh air will get to the O2s causing it to run rich, which will cause a rough idle.

i figured that had something to do with it but i wasnt sure because sometimes it idles and sounds great. thanks!

[Frenchy]

The PCM needs a coolant temp sensor, there's a plug in the back of the passenger side head. So you can run both your adapter for the gauge and the temp sensor.

[myzterray]

The PCM needs a coolant temp sensor, there's a plug in the back of the passenger side head. So you can run both your adapter for the gauge and the temp sensor.

I don't remember if the harness I bought had one on there. I might have to reside and add one. Do you know which pin it connects to in the pcm.

[bstill]

Check lt1swap. It should have what you need.

Oh, and I didn't mean to put rear O2s before. I was thinking the rear of the header/collector and that's what came out.

[pl4yboy]

The PCM definitely needs a coolant temp sensor. You should see all the tables in the tune that rely on that information. You wouldn't believe it.

[molitor]

Just a thought, though everybody else is pretty accurate, I recently had the exact same problem. Turned out to be a failed MAFS, intake temp sensor had died and the airflow resistors had to be be on the way out. In my case is gave me a (MAFS low voltage) DTC. I swapped it out for a spare and viola! runs smooth and drives well again. except for the trans rebuild in progress.

[enc016]

sensors, such as maf, iat, cts, o2's "upstream"
are all relevent to one another when it comes to the engine running as it should. If one sends incorrect signals its a domino effect causing the ecu to try and compensate back and forth for varied readings from the other sensors. id start with having everything you should have "unless its disabled by tune" properly connected, and then see what happens before you start to worry yourself.

I understand the rush after a long endevour to get it running, but dont stress if not all the pieces are in place.
congrats on getting it started. soon i hope to dig into mine.