took off heads, now having a backfiring issue

[480sx]

It first started when i pulled my heads for the third time(couldnt get mls Cometic to seal) and got the car running with the mls gasket. I was tuning idle with megasquirt and the car starts to pop. Sometimes it will hit 3-4 times together. It doesnt backfire all the time, but its pretty consistant at idle only. Switched to an Enthalpy tune and it does the same thing.

Ontop of that, the number 4 cylinder exhaust port on the head seems to be wet, and is the cylinder that backfires most often. You occasionaly see a backfire out of three.

What could be causing this?

[driftingmy240sx]

what engine are you referring to?

[480sx]

The ka24de, no one has any ideas?

[driftingmy240sx]

is your ignition tme and cam timing correct?

[480sx]

Yes timing is dead on, the car ran and idled flawlessly. One day though last summer when i was tuning idle it just randomly started and never went away.

[480sx]

Could a multi layerd steel HG that wasnt sealed correctly be the cause of this? If so, why would it backfire as it does?