Rough Idle HELP! 83 B2000

Ok, i have been through everything i can think of without any luck. Any kind of ideas or insight would be appreciated!

It is an 83 b2000, 4 cylinder, 1970cc


WHAT AM I MISSING? IS THERE SOME HIDDEN AND FORGOTTEN ELECTRICAL THINGAMJIGER THAT NEEDS TO BE REPLACED?

The problem is that the lights dim at idle, and it is really rough!

-It definitely gets worse when the brake is applied; this makes stoping at a light about the worst possible situation i find myself in, it has died a few times.
-If it means anything the worst running is the moment the pedal is released and the lights brighten a bit (and the oil and the battery lights on the dash flash when its struggling hard).
-Upon pulling a plug wire the spark seems very weak at idle, not CRACKING on the block like it should/has before.

I HAVE DONE:
Alternator and Battery are new!
-Alternator was new and i replaced it on warranty because the auto parts store guy tested it in the car and said the volt regulator was kaput; so it is like extra new.
-All connections on battery/alternator were checked, rechecked, tightened and rechecked!
Belt is tight and new-ish
Plugs wires and cap/rotar are new-ish
Ignition coil is original....
WEBER so it aint the carb! Also i checked very thoroughly for vaccum leaks with starting fluid)
Air filter is clean

My thoughts:
As it seems to be connected with the brake somehow I am lead to believe it is the Vac booster, but that line is new-ish and seems to be fine (worked before).

Thanks for any insight, i am at the point of tearing my hair out on this!

Seriousely cnsidering buying a different one around here i saw for sale and swapping in the parts it needs......like my rebuilt tranny and weber.

THANKS!

On my 83 the gas tank was rusted it on the lip around the middle of tank. And it allowed shit into the fuel system and clogged the fuel filter. Mayb check that out. Good luck!!

Get a multimeter and check for resistance value across the ground cable on the battery and the alternator to ground. They should be close to 0 ohms. You may have a bad ground connection.

Ok,
Checked the fuel filter, it looks fine. It is not very old... gas is clean.

I cleaned all the connections and pluged them back in with bulb grease.

OHM's were nill on everything before and after.

ALSO, i took the brake booster line on and off with the addition of gasket maker...

All in all it is a bit better, but the engine definitely stumbles with the brake on; especially when you tap tap tap it a few times!

Thanks!

A weak spark and a 31 year old original coil? I would look into testing and/or replacing the coil. Sorry, I don't have the specs for it.

Check what voltage you have at the coil with the key in the 'ON' position. Does it change much when you press the brake?

Also, there should be a condenser on the distributor that is there to help ensure you get a good spark. Unless you know it's recent, I would put a new condenser on - 15 bucks or less - even from Mazda.

Your vacuum hoses could be mint but you could still have issues with the diaphragms in the booster itself. I would unplug the booster vacuum line and cap it at the manifold. Start it and then see what effect the brake has on you idle.

Picked up a new ignition coil, wires, cap and rotor today; plugs are a month old but ill clean and gap them.

Gonna check the timing, maybe advance it s twinge......

I will check the vac booster as you said before I get into the tune-up later this week.

Also thinking it could be the EGR that is disconnected but still installed..... it'll be a B!t(H but itneeds to happen sometime. Also it'll make fixing the pesky oil leak in the back of the head a peice of cake!

Is there any other normal maintenance things I should do for the coming sping/summer? Just trying to get my truck running smooth not all stumbly and powerless.

Well,

BY FAR THE BEST RESULT AS FAR AS IDLE HAS JUST COME FROM REPLACING THE WATER PUMP!
I noticed one day after a new noise that the pulley WOBBLED and the pump was not happy.
Fan shroud bolts were rusted in place and already stripped so i had to pull the radiator to get at everything..... Easy though, no clutch to deal with just a propeller and a pulley.

Didn't flush the system, just used a nice strong mix of antifreeze and will be replacing it again...next summer.

Idle is smooth as ever, I am going to gap the plugs, recheck timing (stock) and fiddle with the carb-mixture in due time but for now it is purring. Not bad for 228,000 miles!