Trucks Open Question I have an slk200 r171 that keeps losing a cylinder every time I stop in drive however if I put it in neutral it doesn't drop

SOURCE: putting it into drive rpm's dropped to almost

Sounds like you need a tune up,and a throttlebody cleaning.
Use 2+2 carb cleaner to spray your throttlebody until you don't see any black carbon on the throttle plate.

SOURCE: it keeps trying to die when stopped and in drive.

tps sensor maybe

SOURCE: 1999 GMC SIERRA 1500 4.3 AUTO , INTERMITTENT

More then likely you have a faulty throttle position sensor (TPS)

SOURCE: My 2004 outback, if stopped at an intersection,

for some reason you are loosing fluid pressure to the low gear clutch, there are a few things that might cause this most of them are not good, but there is one thing you can do with just a few hand tools, try doing a service and add some transX you might get lucky, we call transX magic fluid in a can. also make sure the transmission is full of fluid. if after trying this there is no change then you are going to have to do what is called a ling pressure test. you do this by installing a pressure gage in the service port on the transmission and and checking the output pressure of the transmission pump. it does take some special tools and a special skill set to go much further. the transmission is pretty complected and i cant recommend trying to dissemble the thing yourself, you could do a lot more damage the good......sorry

let me know if there is any thing else i can do for you.

SOURCE: idle drops lower then normal when i come to a stop but only sometimes

I would check the Idle Control Valve on the throttle body.