Hi, I'm new to this forum, but not to automotive work. I'm a retired ASE-CMAT but NOT FAMILIAR with M-Benz vehicles and systems. About 3 weeks ago, my son was driving my ex-wife's 2000 C280 Sports Sedan, V6-2.8L (98,386 miles) and it 'bogged down' on him when he tried to accelerate into traffic. It had set the CEL lamp and I put my Equus 3160 ScanTool on it and got the DTC codes from it (P0300; P0301; P0302; P0303 Misfire codes). I erased the codes from it and drove it to check it. It seemed to drive 'normally' at low speed and under 'moderate' acceleration..... so I tried to ACCELERATE HARD and see what would happen. Once I accelerated above 3500 rpm, it started to 'misfire', the CEL started flashing, and once it went solid, the engine was in 'limp mode' (cylinders 1,2, & 3 were SHUTDOWN). I pulled over and checked my ScanTool for the codes (see above) and looked at the 'Live Data" at the time the DTCs were set - it happened at 3900 rpm. No other DTC's were set at that time, nor since that time (except a P0410 - Secondary Air-Injection System) as a 'Pending' code, but only during engine 'warm-up' period.

Over the last couple of weeks I've spent several hours reviewing older posts on this forum and another M-B forum about 'misfire codes' and many of them described MAF sensor problems being related to this. Even though I've got TWO rollaway tool cabinets with several thousand $$$ in tools in them, including a wide selection of 'security type bits', I didn't have the "5-POINT SECURITY TORX BIT" needed to remove the MAF element from its housing to clean it properly. I ordered one thru Amazon.com and finally got it a few days ago. During that time waiting for it to arrive, I've been driving the car around with my ScanTool hooked up at all times to monitor 'Live Data' and be able to record it if it failed again. It drives fairly normal, even at Interstate speeds of 70+ mph and accelerates fairly strongly.... as long as I keep the rpm below 3000-3500 rpm. I have deliberately tried to ACCELERATE HARD just before arriving home = and IT ALWAYS DOES THE SAME THING..... CEL first flashes a few times, goes solid, then engine runs like crap since the ECU shuts off the FUEL INJECTORS for cylinders 1,2, & 3. If I pull over, stop, shut off the engine for a minute, restart it again, the CEL is ON, but I can drive it again 'normally' with all cylinders firing normally (unless I accelerate 'hard' again).

I finally got the 5-point TS bit socket set and removed and cleaned the MAF element thoroughly with MAF Cleaner, reinstalled it, and then drove it around again. Everything was 'normal' UNTIL I ACCELERATED HARD ABOVE 3500 rpm. Since M-B parts are ridiculously expensive, and since it NOT MY CAR, I'm a little hesitant to start replacing parts on it without some guidance from some of you MB owners who have more knowledge of these MB vehicles than I have.

I've read these forums quite extensively and have even tried the "ECU Reset" procedures just to see what would happen. I did notice a change in the lower speed shift-points being 'quicker' and more solid and made sure to keep it below 3500 rpm until I got 'close to home'. When I tried accelerating hard again, the misfires codes and CEL returned. The 'Live Data' on my ScanTool always shows it happening between 3800-4200 rpm. Other than this, the car starts and runs quite well.... as long as you DON'T ACCELERATE HARD.

Here's one thing I'm noticing about the 'Live Data' readings I'm getting on my Equus 3160 ScanTool - the 'Advance' is always displayed as '-' (NEG) in front of the DEGREES OF ADVANCE reading. I checked this on two other vehicles and this ADVANCE displayed normally without the '-' in front of the displayed 'degrees advance' readings. Is this an 'incompatibility' with my ScanTool and the M-B ECU or what?

I've bought a set of Bosch +4 Platinum spark plugs for it and am going to replace them tomorrow and try also switching the 'coil packs' from the passenger side (bank 1) to the driver's side (bank 2) and vice-versa, just as an experiment to see if the DTC codes 'switch' with them or remain the same - this WILL CONFIRM WHETHER THE COIL PACKS ARE GOOD OR NOT. I've even purchased an AllDataDIY subscription for this vehicle, but even it hasn't provided much guidance in troubleshooting this problem since I don't have the M-B 'special tools' needed for it.

I've got to try to 'fix it' before my son returns it to my ex-wife in Atlanta or I'll never hear the end to her "B----ing about it being returned 'broken'."

I have all of the basic tools and knowledge (24 years Avionics and 40+ years auto tech background) to check anything out.... I just can't find any info as to what the voltage readings should be at various connection points to test the various suspected components properly.

Any help or guidance in troubleshooting this C280 is greatly appreciated. There seem to be some very knowledgeable people on these forums. I read about a decent $$ source for parts (near AZ, I think) but can't seem to locate it again. The local M-B dealer wants $460 for a new MAF assy, $222 for a Cam Position Sensor, and $243 for a Coil Pack.