Hi

My mother in-law has a 1999 Merc a class, recently i have been reapiring it due to rough running and black smoke exiting the exhaust on idle, on my code reader it said that the lambda sensor was the fault so i changed that i also noticed the colant temp sensor moulding was cracked so i replaced that to no avail, i heard about a common fault on the a class that the mass air flow sensor can go faulty, i sent the ecu/maf sensor off for repair £350 later i get it back, i fitted it today but there is still a problem, it starts and idles fine with no black smoke but it will not accelerate unless you pulse the peddle, i removed the maf sensor with the ecu part still connected and it accelerated fine with no air going through the maf, i then put it all back together and it was still fine and it drove lovely and pulled well, i came back to it about 2 hours later and tried it again but the problem has come back, i can keep doing this and it will only work for a few hours, any help would be greatly appreciated

Thanks Dan