My car boggs and lags. If I keep pressing throttle genteelly it revs up but if I press it normally it bogs and picks up after quite delay and some time does not picks up. When pressing throttle it first drops rpm and then picks up.

What I have done so far
1. Changed Distributor Cap, Rotor, Coil and ICM
2. New Spark Plugs
3. New Spark Plug Wires
4. Cleaned Throttle Body

Car is OBD2B so it adjusts its timing itself I cant do it. Spark Plugs are light brown sooty color.

Never tested Injectors or Fuel Rail.
When engine is Off and switch is on I hear sssssssssss sound from fuel rail. Suppose its normal or perhaps some injectors are stuck open.

where should I start then.....

 

Check all your engine grounds, make sure they are clean and tight.

 

already done that......

 

Cleaned Fuel Injectors, Fuel Rail, Checked voltages at Pump they are 11.7.

One thing I noticed that there are continous bubbles going to return fuel tank after fuel pressure regulator. I have transparent pipe there.

 

Maybe your FPR is bad? Could be letting air in/fuel into the intake.

 

It could also be water in the fuel tank. Try a dose of Startron or dry gas.