Idle & Low rpm miss fire - Bigport

[FUTO_GT]

AE82 Bigport motor only has 20,000 on it since rebuild.
TVIS is hooked up, RWD manifold from JDM biport, Installed and wired in by me ~2 months ago,
has developed a idle and low rpm miss fire in the last 2 weeks. Any thing over 4000~4500rpm is
clean and free revving, anything under 4000 will not hold even rev and misses. I changed plugs,
leads, dizzy cap and rotor but still does it. I didn't wire up the Diagnosis plug, so don't know if its
throwing a code
When driving if it has load on it then its OK, but cruise it will miss. It feels a
little bit rich, 1st to 2nd, 2nd to 3rd will pop a little back fire between gears driving sedately.
Timing is set to 0 on the marks, runs on 98 octane only, no pinging and has heaps of power, but yeah...

I noticed if I pinch the MAP sensor hose the revs clean up and the miss at idle
goes away, also it will hold clean even rev @ ~2500-3000rpm (can't see tacho).
I have the MAP and the stock FPR T pieced together off 1 brass fitting in the
back of the manifold. I was told that full vacuum signal to the FPR will make it
run choppy at low rpm? Could this be my issue?

Does anyone in Brisbane have a Bigport MAP sensor I could borrow and see if
this is my problem?

[Nikkojoe]

Could be a problem with the map sensor but best to check all sensor earths and make sure they are all fine.

Pinching the map sensor line - the result seems odd as it should be the opposite to what is happening. Cutting vac to the map sensor will cause it to run in limp mode and give a default fueling map, and it will miss under constant throttle.

Could well be a faulty map sensor, or the ecu could be old and capacitors leaking. I would take the cover off the ecu, inspect for bulging capacitors and if possible swap ecu's with someone.

[FUTO_GT]

If I pull the MAP hose off it will drop the idle down, fuels up and stalls out..
Does the MAP usually go to FULL vacuum signal?

[Nikkojoe]

FPR and MAP are seperate on the 3way vac block.

[FUTO_GT]

Yeah, I reinstalled the 3way, no change, still missing...
Tried unplugging ECU for 10min, still does it.
I changed the coil to a Bosch one, wasn't that.
I'm going to change fuel filter today and hopefully someone
has a spare MAP I can borrow to check and see if its that...

[Skylar]

Tear in the MAP line?

running O2 sensor?

Completely unrelated but shouldn't timing be at 10 deg btdc in diag. mode?

[Nikkojoe]

Should be set at 0Deg in diag. mode, which then once out of it should be 10deg btdc. Setting 10deg in diag would make it about 20deg normal (awesome torque though )

[driftke70]

leak in inlet, could be as small as a hairline crack, is your rwd manifold braced to the block?

[FUTO_GT]

Through process of elimination I disconnected the TVIS which has helped
with cruise.

I disconnected the sensor next to the cold start injector, biggish yellow plug,
this also has helped some.

Right now, its running better than it was, idle(~900) -2000rpm is smooth,
if I try hold a rev over 2000-4000 it will miss, its only a tiny miss, but its shitting me to death.

I'm getting a compression test done tomorrow and might clean the injectors also.

Are 4afe grey top injectors the same as the 4age bigport grey tops?

[Skylar]

So what should one set the timing to when engine's warmed up and in idle mode to get the same reading as being properly set in diag. mode?