I'm having an idle issue whenever going in and out of gear. When going in gear the engine will idle. When going out of gear it won't cleanly pick up idle speed. If you just lightly blip throttle it cleans up.It's 4150 ,950 [830], IAB 70,MAB 28, IFR 31 lower, mix screws 1.5 out [ yes I'm on the idle circuit] mix screws are responsive. Fuel pressure 5lbs holley blue pump. Floats halfway up sight glass. Idle timing 25, 34 total. 446 Indy EZ heads, Mopar 590 cam, TorkerII intake with 2in tapered spacer. 8 in convertor 5200 stall. Idle speed is 12-1300. drops to 800 in gear. 8in vacuum at idle. MSD pro billet dist,6 AL box. What is blipping the throttle telling me?

Try going down on the IAB a few thousanths, see what it does.

You're thinking it's a tad lean?

The distributor advance mechanism needs to set to there is no change in timing within that idle in gear/idle in neutral rpm window.

In other words...... same timing at 800 as 1300.

My suspicion is that when you blip the throttle in neutral, several degrees of timing get added in........ as a result, the signal/vacuum is increased.

I'm running one light spring and one medium spring. 2 light springs and it's worse. So it sounds like I should try 2 medium springs. I understand what you're saying 25 @ idle needs to be @ 25 in gear also. I have a 10 degree bushing in the dist. Locking out may be an option.
So I tried what Fast suggested. Went with 2 medium springs. Rpms pick back up quickly. Still have about 3-400 rpm drop from out/in gear. Mix screws are extremely sensitive now.

make sure distributor weights aren't sticking due to hard grease/lube, dirt, etc.
i have seen that problem quite a few times over the years.

My MSD Pro-Billet timing would bounce at idle, and the phasing was way off on the rotor.

What are you running initial and total? Any vacuum leaks at the usual places?

I had to use the MSD adjustable rotor to get the phasing corrected and I ended up locking out the distributor to get rid of the idle timing fluctuation. I even had a collar on the distributor shaft to help stabilize the timing, which did help to a large degree.

I've since switched to a Progressive Ignition distributor to gain easier adjustability and vacuum advance. It's been amazing so far, and the gauge feature is a great aid to tuning.

I'm running 25@ idle, 34 total. Timing fluctuates about 1* I put 2 medium blue springs in and it stabilized the out/in gear idle. No vacuum leaks that I can find by spraying starter fluid around. I'm trying to avoid locking out because I'm still running an oem starter. Not an easy change on an Abody with TTi chassis headers. I'm going to experiment with the dist springs whenever I can get another experienced racer to work the throttle and watch the tach or work the timing light. I'm much happier with the idle quality after the changes, the throttle sounds clean and not blubbery whenever you slowly roll into it without bringing the pump shot into play. The mix screws are very sensitive 1.5 out. I have read your posts about Progressive dist, they sound like a quality piece.

Maybe it’s just how I’m wired.......but.....

With a 270@.050, 106lsa cam........ I wouldn’t be letting the thing chug along in gear for any length of time at all.
Stop lights.....neutral.
Moving up in the staging lanes........ move up, then neutral.

Motors with rowdy race type cams don’t have to idle all that good in gear for me.

As long as it doesn’t l stall after the burnout....... I’m good.

Been there done that with a 260 degree @.050 intake and 266 @ .050 on the exhaust ground on a 108 LSA installed at 107 ILC. I ended up using the Mr Gasket 925B really weak springs in my distributor and it was idling 16 BTDC with 34 degrees total. Before using those really weak springs it would vary like the OP is having
Good luck on getting yours the way you want it, YOU can do THIS

Make absolutely 100% certain you have no vacuum leaks.
Because if you do have one and can't find it, it's possible for a person to chase their tail for awhile.

I once had a carb gasket (the paper one between the main body and the baseplate) fail and act up like this, and no amount of normal
testing from the outside would reveal the leak. Had to change the gasket to notice the improvement.

I once had a valley pan gasket leak, but the leak was from the underside on #6, not the top where people try to check them.
I could not find it until I literally sprayed water with a hose in that area. Carb cleaner and such accomplished nothing.

If you're sure it's definitely not a vacuum leak:

You probably have 25 degrees advance at 1200, and it seems to idle OK,
but when you drop it in gear you only have 10 (or something/ similar small number) at 800.

Enlist a helper to hold the brake with the car in gear, while the timing is being checked.

I'm going to guess....it may have a whole lot less than 25 at 800 (meaning at 1200 the weights
are partially out, which is no bueno).

If you lock the advance mechanism in the distributor and run 34 all the time as alot of
race applications do, you might like that. Or you might want to try the lightest springs you can find
to bring all the advance in at idle, and still retard it while cranking.

I hear you about the stock starter being suspect to cranking the motor with the timing locked out. Just insure that you have the proper sized ground and power cables going to the starter as a general rule. I never liked changing the starters in my E-Body with big tube headers, let alone an A-Body.

I had to use the 4 Seconds Flat distributor bushings to get my initial up into the low 20's and limited to adding only 10 to 12 degrees of mechanical advance. You stated you had a 10 degree bushing in your dizzy. Is it one of the bushings that came with the MSD unit? If so, your mechanical advance must be more than 10 to 12 degrees additional advance when fully advanced, which makes me suspect the post above this by Zippy may have identified your issue regarding the timeing dropping lower than where you believe it is..

I'm using the bushing from 4 second flat 10*. So I have a lot of initial 25 with 34 total. Now I just need to get a friend to stop by so it can be checked whenever I drop it in gear. Then verify when it's all in. Then play with the springs some more. Sprayed starter fluid all around intake and base of carb no change in engine. Only 1 vacuum line for pcv. Fast you're exactly right, I try not to idle it around and do the neutral bump, but I also don't want it stalling after I do my burnout as a courtesy to the other racers.

With the set up you described, I can't see the timing dropping below that as a result of the rpm drop when going into gear. The 3800 rpm stall torque converter on my Magnum doesn't drop the motor rpm when it's put in gear. Is yours correct for your combination?

Two additional things you can do are to install a shaft collar and adjust it so it allows about .015" play for oil to get between the gear and the bushing, and verify your rotor phasing using an old distributor cap with a 1/2" or larger hole drilled in the top of it near #1 terminal.