Rough Idle

[timwds]

Check your intake manifold bolts and try spaying some water around the gasket whiles it's running to check for leaks.

[SuckSqueezeBangBlow]

I have a miss at idle only when in D and gets worse when AC is on, in Neutral is mostly fine.

Hoping to eliminate it, I've just done:

engine mounts (stuffed anyway)

spark plugs (genuine, and probably didn't need doing but probably halfway through their life)

coils (genuine, and needed doing anyway)

TB clean

I'm going to try the water trick around the intake manifold gasket.

Its annoying.

[timwds]

A manifold leak will normally get better with load because the vacuum is reduced. Roughness that gets increasing worse with load suggests either a spark or fueling issue. You could also try dumping bottle of nulon injector cleaner in a full tank of fuel, it has worked wonders in the past. I haven't had injector issues with Falcons before but have with many smaller cars (corolla etc), worth a shot if nothing else works.

[Ralph Wiggum]

I have a miss at idle only when in D and gets worse when AC is on, in Neutral is mostly fine.

Hoping to eliminate it, I've just done:

engine mounts (stuffed anyway)

spark plugs (genuine, and probably didn't need doing but probably halfway through their life)

coils (genuine, and needed doing anyway)

TB clean

I'm going to try the water trick around the intake manifold gasket.

Its annoying.

Is your car tuned/modded?

[SuckSqueezeBangBlow]

yes autotech tuned 280rwkw. bosch 968s, cat, 12psi