Another Possible MAS Problem?

[Dave Bailey]

I have a '98 C280 V6 that does some odd things from time to time. After reading through some of the other threads on the forum, I'm beginning to think that the MAS could be the culprit. The symptoms are that occasionally, I will experience very jerky shifts between 1st and 2nd gears. Downshifts are often worse than upshifts. This seems to happen more often if I get stuck in traffic. Also, the car sometimes refuses to pull cleanly in 2nd gear. It doesn't matter if I manually select 2nd or kick down into it, the car hesitates and wheezes its way up to about 5000-ish rpm. It won't pull to the red. Once into third gear though, she pulls like a train. The final observation is that kick down itself can be an unpredictable business, sometimes it works correctly, other times nothing happens at all. The gearbox oil and filters were changed about 25k back, so things ought to be ok in that department. Does this sound like classic MAS failure on the horizon, or should I be looking elsewhere? If I should check the MAS, is there a fairly easy home spannermans method, perhaps some visual indication its condition? Finally, I've seen some references to the possibility of cleaning the MAS. Is this a viable option, or will cleaning attempts merely send it to an early grave? All suggestions will be greatly appreciated as usual. This problem is driving me nuts.

Thanks in advance,

Dave

 

[chatteris]

My 98 c240 sometimes would not accelerate after kickdown and would sometimes be slow to change up at 6000rpm I cleaned the MAS with carb cleaner and there was a slight improvement so I cleaned it again with brake cleaner and it was better again, the hotwire didnot look dirty but a good soaking in cleaner seems to have worked.
I think there is a MAS problem with mine but most of the time I dont notice any problem,The other half usually drives it and she is a fairly sedate so until it gets any worse I will live with it.

 

[silverarrow]

for a cheap fix look atwww.bba-reman.com
best £100 to spend
can even send yours for a on bench test

 

[Dave Bailey]

My 98 c240 sometimes would not accelerate after kickdown and would sometimes be slow to change up at 6000rpm I cleaned the MAS with carb cleaner and there was a slight improvement so I cleaned it again with brake cleaner and it was better again, the hotwire didnot look dirty but a good soaking in cleaner seems to have worked.
I think there is a MAS problem with mine but most of the time I dont notice any problem,The other half usually drives it and she is a fairly sedate so until it gets any worse I will live with it.

Mine won't always accelerate after kickdown either. And come to think of it, I've experienced reluctance to upshift at 6000rpm from time to time as well. I'll have a go at cleaning the MAS to see if it improves things. If it does, I'd best start saving my pennies.....

 

[Dave Bailey]

for a cheap fix look atwww.bba-reman.com
best £100 to spend
can even send yours for a on bench test

I'll give them a whizz if cleaning shows an improvement. I've asked them for a quote anyway, since they don't specifically list my car on their website. Thanks for the pointer.

 

[Dave Bailey]

Update -

Knowing my luck, this won't be the final cure, but..... I took the MAS off the car last evening to find the part number as BBA reman want it before they can quote me a price for a replacement. Upon unplugging the MAS, I noticed that the contacts in the connector looked a bit dirty. So as a matter of course, I cleaned them. This morning, the car is behaving like a different beast altogether & drives a lot more like it should. As I say, this probably isn't the end of, it but I'll live in hope. Thanks to Chatteris & Silverarrow for your useful tips, much appreciated.