SLK230 Misfire...

I have a 1999 SLK230 that misfires. I've noticed that it does so under these conditions...

1.) when it reaches 3,000 rpm
2.) and when the fuel gauge reaches the 1/4 level

I've had it serviced four times. They said they've changed all the spark plugs, engine coils, filter(s), and cleaned out everything that needed to be cleaned out. They would return it to me without the misfire but it does it again after about a week or so and then I return it to them and they say they don't know what is wrong with it.

I always put premium gas (the number rating, I forget) and I have tried switching from Chevron to Shell to 76 gas stations and it still does the same thing. I've brought it to an outside service mechanic who specialize in German cars but they still have no idea what is causing the problem. They always say, they think its this or they think its that but they never know exactly how to fix it. In the mean time costing me more $$$$.

Please help! Any suggestion/input/ideas is welcome....

Thank you...

the check engine light is on?

does it misfire from intake or exhaust?

have they tried using a known good airmass sensor from another car for test?

Sound like MAF to me too but Ive heard of strange probs from leaking fuel cap so maybe try another fuel filler cap.

Bazzle

Yes the check engine light is on.

As far as it misfiring in the intake or exhaust. I have no idea. I was told that the gas pressure was suppose to go up to 52 and its only going to 48. And its not reaching Pin # 1. Whatever that means. So the fuel pump was replaced (another $400) and it ran fine for a couple of days, then it started misfiring again.

MAF? sorry I'm not very knowledgeable in car lingo... What is a MAF?

mass air flow.

Like this

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=4624466895&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1

Bazzle