Engine Shaking at Idle...

[Blackbird]

G'day Everyone,
My legnum has had a problem for quite a while and Whilst I've been methodically working through different things it's getting to the stage where I'm running out of ideas.
car is sitting at 56,000km atm. Manual.
Car isn't tuned yet.

it has a shake (a bit like a miss) at idle, It's more pronounced after driving at FWY speeds so everything is hot.
It's not a miss per se.. as you'd hear the puff from the exhaust.. tail end, car sounds perfect, and hasn't lost power and doesn't stall. Idles at 600-650rpm all day. it's just noticeable enough to get worrying.. but not stupid .

Stuff I've done,
Checked and cleaned coil packs, added dielectric grease to the plugs and leads.. As per the manual they are all within spec, no scorch marks on anything. though I'm going to replace the rear bank leads this weekend as I really want to add some silicone to the inlet manifold gasket at the same time. Seems like a vacuum leak to me but I just can't find the bugger...

3SX fuel rail, I think when I changed that it started then.. no fuel leaks but something was disturbed I'm thinking...I've triple checked everything since...

New intake manifiold gasket when I changed the plugs too... torqued down to spec..
New VK-22 plugs, no oil leaks in the plug holes or anything.
Replaced all the intake plumbing clamps and checked for cracked hoses
Cleaned fuel injectors with new seals One was rather dicky at the time.
New front mount with new clamps and hoses
Checked TPS ok
New fuel /air filters x 2 times
New DW200 fuel pump, starts first crank every time! Car sat around a lot in Japan so figured maybe corrosion was affecting the pump.
I added an electronic boost sensor early on.., swapped that out with another.. still no help.
Throttle body is spotless.
Tried using different brands of fuel.. nup.
Checked timing belt.. looks new no cracking inside, and it's timed correctly.
Checked all vacuum hoses
cleaned and reseated the PCV
Evo 9 BOV was added.. from my old car.. seals ok
Checked and cleaned and lubricated the big o'rings that seat inside the Turbos to the outlet pipes no help
MAF is spotlessly clean and reads as per the manual with a multimeter.
Checked almost all of the plugs in the engine bay looking for corrosion.. nope
Checked proper grounding... no help
Car boosts ok with no loss of power, returns about 10.6lt/100km around town and doesn't behave erractically whilst driving... just the lumpy idle that's not consistant.. more random shakes.
Car is serviced with Nulon 10W-40 synthetic and a new oil filter every 5000km... engine is like new inside.
It's not losing coolant either....
There's probably a few other things I've missed here but keen on anyone chiming in with another idea..

Car isn't throwing codes either.
What have I missed??

Any help would be greatly appreciated..
Thanks guys
Steve

 

[Jakevr4]

Get the injectors cleaned/flow tested, i bet one is way out of spec compared to the rest.

 

[Blackbird]

Thanks mate! They were done about a year ago... only a few cc difference between the group...
Think I've found the issue... bung ignition lead..
not enough to cause a miss but enough it was arcing out on the inlet manifold where the clamp sits..
Going to take it for a drive later today hopefully and see if that was the cause....

 

[jet150]

Good to hear you solved it. Leads should be one of the first things to check

 

[Blackbird]

Umm seems like I spoke too soon.. The VAST majority of the shake is gone but some has remained...
As for the leads, the all measured under 16k ohms with a multi meter... well within spec but one was arcing out to the engine... glad I've changed them out.

Think the rest might be a vac leak...
Unfortunately I've partially stripped the two long bolts that hold the plenum on... ordered longer bolts in the hope that the holes are drilled and tapped a little deeper than stock... if not it's helicoil time lol...