Fluctuating Idle Problem - 2000 Civic

[00Civic]

UPDATE:

Installed new transmission ( with Honda MTF - TY Chris! ).
Installed P06 (OBD 1) ecu w/jumper harness.
Installed new axle.

I am still having a fluctuating idle, and I'm still scratching my head on this issue. Anyone have any ideas? I don't have a throttle body gasket , and am going to pick up one tomorrow. I'm hoping this will solve the issue. My brother peered inside the throttle body and said there wasn't a gasket. Would this cause the fluctuating idle?

Also, I have a custom header ( with no oxygen sensor bung ) and no primary oxygen sensor, but my secondary oxygen sensor is already plugged in. Should I wire up the primary to the secondary so that it reads as one? Would the missing primary oxygen sensor be causing the fluctuations?

I need guidance!

[*EFilliated*]

a throttle body without a gasket would definetley cause the idle problem, that is considered a vacuum leak. the missing o2 wont cause the idle problem but ur car will be off on air to fuel ratio. if u have a CEL for o2 fix it

UPDATE:

Installed new transmission ( with Honda MTF - TY Chris! ).
Installed P06 (OBD 1) ecu w/jumper harness.
Installed new axle.

I am still having a fluctuating idle, and I'm still scratching my head on this issue. Anyone have any ideas? I don't have a throttle body gasket , and am going to pick up one tomorrow. I'm hoping this will solve the issue. My brother peered inside the throttle body and said there wasn't a gasket. Would this cause the fluctuating idle?

Also, I have a custom header ( with no oxygen sensor bung ) and no primary oxygen sensor, but my secondary oxygen sensor is already plugged in. Should I wire up the primary to the secondary so that it reads as one? Would the missing primary oxygen sensor be causing the fluctuations?

I need guidance!