129 300sl Engine splutter and misfire after left idle for a week or more

[caesarang]

Have a 300sl 24valve. Been loving it. However I don;t get to enjoy her much. I normally give her a short run on the weekends. Sometimes I leave her idle for up to a month at times. The usual problem I had with her is that upon start up, she feels ok. She will run fine for about 3km then if I;m on the highway she will splutter for a like 10 minutes then she'll run fine and continue to run fine if i drive her continuously the next day and so forth until i put her in storage for a week and the symptom will return.

Sometimes if I do run her after a week as usual she'll run fine for the next 3km and if I'm unlucky I do come to a stop she'll splutter and the the engine will definitely die off. Sometimes it'll be difficult to restart her even though she has warm up. Left at idling she sounds fine but start revving her up she'll splutter and mis fire at 3-5krpm. sounds like she;s choking. then after 5 minutes her chocking will disappear then she wizz by as usual.

Then again if I do leave her for a week or more again and do start her up but do not immediately drive away and leave her idling, she will definitely splutter after 10 minutes even at stationary. She can die off too. Mind you she only splutter upon revving and not at idling. when i check the exhaust the floor is really damp and it smells of unburn petrol.

I am basically out of my wits as to what is going on. She'll run fine after that initial spluttering and misfiring after being left idle for a week or longer. Other than that she purrs and sounds smooth.

Would appreciate any ideas you have!!

[AJG382]

This could be a number of things. But the first place I would look is the Distributor Cap and rotor.

[ctaylor738]

Second that, also look closely at the insulating plate behind the rotor for any signs of arc-ing or cracking. Next steps would be the fuel pumps and the airflow potentiometer.

[texasbernie]

I have a 1990 300sl and had the same problem, I tried everything regarding fuel parts, etc. The problem was the Rear Crankshaft Sensor. I replaced this part and the car runs great!