ml320 - unstable revs at idle and when driving

[shark]

I have an ML320, 1999, 130,000 miles, which is currently exhibiting the following symptoms.
The car idles at around 700rpm, then the revs will drop to around 300/400 and then over correct itself to 1000rpm then drop down to 700 again - this takes about 1-2 secs. It does this intermittently. If I have the car in drive and I am holding it on the brake ie at traffic lights and this happens the drop in revs tends to stall the car.
This rev drop followed by correction or over correction also happens while driving. This can be a bit disconcerting as the drop when driving is about 400-500 revs and then when it corrects the gearbox kicks in with a bit of a thump. If driving very slowly with full lock on the car will stall when this happens. This can happen at any speed up to around 80mph. I dont usually travel much above this speed...
I have previously experienced faults with, and replaced, the MAF, O2 sensors, crank and cam sensors and faulty cats. The symptoms here are different.
Please help.
Many thanks in advance.

 

[shark]

Ok everyone, I finally got to the bottom of the problem, after 3 days at the stealers they said that the only thing that wasn't quite right was the MAF which was operating at the limit of its range. They wanted £350 to replace it which I wasn't too happy about as they couldn't say for definite that was the problem. I found my original MAF(rough running etc) in the garage, I thought I had thrown it away, and swapped it over. The current symptoms disappeared but the engine did run a bit rough which was the reason for changing it previously. Stealer wants £250 for the part but as the last one has only lasted 2 years I've decided to get an aftermarket one from ebay for £50. I'll let you know if its ok when it arrives. By the way, I tried to clean both faulty MAF sensors with carb cleaner and isopropyl alcohol and neither saw any noticable improvement.

 

[jibcl500]

Well done, do a search on MAF or air flow meter and find out whats been said in the past. They come from china!!!!! the land of many things CR@P.

ijb

 

[shark]

Well the new MAF is fitted and it works, the only thing thats not quite right is the gear changes dont seem as smooth, or maybe thats just me trying to find fault.