Hello, I am a newcomer here at the engine talk, come from the front Eifel and like to screw around cars. Up to now almost always with success, but on the weekend I bought a problem child: Mercedes SLK 230 Compressor Mopf BJ 2001 230000 km. Only very little rust. The price was cheap. Known defects ZV and roof is not possible. Tüv completely new and during the test drive everything was OK. On the first 50 km motorway ride I noticed that the SLK did not get particularly fast. The next day the following thing happened: car starts to stutter after 20 km and runs only on 3 cylinders, while trying to drive home a lot more then a cylinder. In the error memory is the ignition dropout cylinder 1 and 2. So first of all ignition coils and candles out. The candles look new (and are also not wet). So candles again in, and ignition coils of 1 and 2 with 3 and 4. Error memory deleted and After a few seconds normal engine run again only 3 cylinders at the run. A little later then again only 2 cylinders. In the error memory again ignition oscillators 1 and 2. Despite changed ignition coils. In case of defective coils now cylinder 3 and 4 should have been in the error memory. In all further tests I found that the engine runs better when I clamp the air mass meter. – So I knew it must be on the LMM. So a new besor gt and built-in. Unfortunately, that didn’t work. Does anyone have any idea what the ignition triggers can still come from? Maybe injection nozzles? Does anyone know if the PSE ZV pump also has something to do with the roof function? In the troubleshooting of the central locking I had to find out that the pump in the car is completely missing. If the PSE is only responsible for the ZV, I could do without the expensive part and stop manually on and close.