Hey guys, so i have my SEC that i have been working quite allot on, many parts have been replaced as this car had been sitting for 15 years before i got it.

The problem:
When the car is cold it starts nicely and the idle is stable, however if i press the pedal it will start to stumble and make a deep "pop" sound if i press it for too long, as the car heats up it gets better and better, and when fully warm its like there is no issue at all.

The things i'm looking at now that can be the cause of this is either
-The warm up regulator, i have not been looking much at this part, it could be dirty or hanging after years of not being in use, but mine is very simple, only got 2 pipes going from it on top, and i understand that the unit itself is simple, so i think i maybe a good cleaning can help, but i don't know.
-I have a frequency valve on my car, when i disconnect it nothing changes, it basically has the same function as the EHA valve on the gen 2 cars. Mine it originally a Japanse car, so it has some of the US emission gadgets on it, however i have no O2 sensor, no control unit under my passenger footwell, no EGR, and from factory it did not have a cat, i had a universal one on mine that i've removed.
-I replaced the ground cable in my car, and all of a sudden my interior lights started working, when i was playing around with the buttons inside i could clearly see that the light would flicker if i turned something else on, and with many things on the light would be quite dimmed down. So the power in the car is very weak, that makes me think that it might affect the spark plug wires, and other things i have in my car, i hope a new voltage regulator can solve this, if not i will buy a new alternator, from a newer MB, the w126 alternators put out so little amps

Please help me with this, i am without a car now and this is the only one i can use. So i'm very dedicated to get it fixed.

Things i have done:
-New fuel pump
-New fuel filter (previous was from 95)
-Cleaned the fuel pipes
-Drained and washed the tank
-New fuel pump relay
-New OVP relay

-New ignition wires
-New spark plugs
-New rotor and distributor cap
-New Coil
-Timing adjusted
-New cold start valve
-Cleaned idle control valve

-All new vacuum connectors and gaskets, there is no vacuum leaks.

Hope someone can share some knowledge here