w140 600sel please help

[grws]

My car has had the secondary air injection pump replaced recently. The car started a problem where it would start perfectly but once it ran for about 5 minutes it would start to miss. I was told it was the cat. The one cat was replaced and was fine for a few days and the problem sarted again. I was informed it could be the other cat...so that was also replaced. The problem persists!! If I rev the car and the revs reach +/- 2000rpm it smoothes out but as the revs lower it misses again. I floored it the other day and it seemed to clear itself and was fine until I started it the following day!!! What can the problem be? Can anyone help please? I live in London near Chertsey.
Thanks
Glen

 

[jibcl500]

It sounds like a problem Im having with a W140 S500, tickover is lumpy, sometimes stalls for no reason, sometimes the ESP light are on the dash etc.
Plugged the laptop in and found nothing, replaced all the plugs as they looked rough, swapped the ignition packs for known good ones, no change.
Found a split breather pipe on top of the engine, replaced it but it made no difference, removed the same breather pipe from my CL and it ran the same as the customers car, so I assume there is a breatehr pipe somewhere that is leaking, if you can hear a sucking sound whilst the engine is running on tickover then that could be the fault.

jib

 

[grws]

Hi jib...thanks for taking the time to reply. I was told to add a bottle of Cataclean (bought from German and Swedish) to the fuel tank, which I did and miraculously it has cured the problem. I let the car run while I was washing her and occassionaly brought the revs up and after about 10 minutes she settled down to a smoothe idle. I will however take your advice anyway and check the breather pipes. Thanks
Glen