400 idle speed

You might get a quicker response in the 400 section, try there as well

 

FWIW/FYI-
reduced air flow-pretty simple actually...

the car will need to be retuned utilizing a 12 cyl mercury manomter...
without which, your time and effort will largely be wasted...
this is a job requiring skill, tools and experience typically ouitside the purview of the average DIYer
(DLR cost for a factory, filtered and with evap traps{mercury's boiling point drops steeplywith vaccuum. Boyle's gas Law} using mercury was 5000.00 USD in 1990-94)

You wil also need a gas analyzer with ports at each exhaust pipe at head flange...lastly, no one with the requyisite experience is likely to even start this without removing the distributors and sequencing them on a distributor machine first-as 95% of ALL carb problems
are found to be in the distributors!

 

You changed two things.
1) you went to individual filters which will draw more hot air that the originals which means you need to lean it a bit.
2) you also opened up the air passage by having clean filters which means you need to lean it a bit.
My guess is you should go around and turn all 12 idle screws the same amount in, say a quarter turn and see how that does, if not try another quarter turn on all screws. If you do not like what you have done you can put it back to the way it was if you pay attention.
I would try that before you spend the big money.
Good luck.

 

I think you still need to get a timing light on the engine and confirm smooth operation of the timing advance on both banks. They need to be pretty close. I don't believe one can assume timing is correct until confirmed with a timing light and tachometer.

What's the timing doing at idle and off idle. Where does it start? What the advance at 1000 , 2500, 5000 rpm? Timing going up in rpm is more important than going down in rpm.

Is the advance smooth, or jumping around, or a lot of hysteresis?

Bill

 

Do not mess with your ignition timing. The car had "butter smooth" idle before. The only thing you did is change the air filter which would only effect the air/fuel ratio. So it would be logical to make changes on the air/fuel mixing system.

The factory jets were determined with fuel that did not have the alcohol we have today. Alcohol requires more fuel. Going a step up in a fatter jet for idle makes since in more ways than one. The clogged air filters, with the dense cool air of the original air box's kept you closer to the needed fuel air/ratio.
The trick in tuning is not to do to many changes at one time so you can see the results of what each and every adjustment makes.
You are going on the right path in the right direction. Do not get distracted.