just with in the last 25 minutes of driving im at half a tank of gas and when im sitting at stop lights not every one but some the car start to shake and the tach jumps between 1000 and 300 rpms. then once when i started to go it started very very slowly and didnt pick up till i was at about 3500 or so. anyone have any imput or thoughts on this?
Thanks!

 

happened to my moms 94 c280, brought for a full tune up and the shaking was gone.

 

May be in need of a good tune up, as mentioned. Could also be fuel pump going bad, clogged fuel filter or injectors, or just plain ol bad gas..

 

CLean your IACV and throttle body ,try turning the lights on to activate your idle up circuit or A/C.