w210 manual idle/throttle controller?
 

I have a 96 300E. When I start it when its cold out (below 80*) it runs VERY rough after the glow plugs cycle off and idles around 600prm. Has anyone heard of an aftermarket throttle control like I have in my 1980 W123? When depress the accelerator and bring the RPM's to around 1500 rpm she idle's smooth and when the engine warms up after about 3 mins, she's good to go. I'm just looking for some idea's for when I can't plug in the block heater like when I'm at work.