Engine shudder issue

[kobsman]

Hi Everyone!
I am new to the forum and i need help with my 1999 ml320. The probem is that at a standstill with my foot on the brakes and with the transmission engaged, I hear a distinct intermitent click noise that comes from the engine compartment. when ever I hear this clicking noise it causes the engine to shudder causing the whole truck to shake. I have changed the plugs (not the wires though) , cleaned the egr tube and also replaced the MAF. Still no sign of improvement. I have also recently started experiencing rough start up that is the engine starts and attempts to stall immediately then revs up high before it settles down. I will appreciate all help on this issue cause I reccently lost job and cant afford to go to the dealership. Thanks