Hi everyone, how are U doing ? I am new to this message borad, please bear with me.

I have a 86' 420 SEL with 173K miles on it. I bought it used about 9 months ago with a slightly rough idle problem (a discout price.) -- no matter hot or cold.

This car has -- new Timing Chain (double role),
new BOSCH 4-ground Platinum spark plugs,
new Valve cover gaskets.
new Ignition Coils, wires, Cap & rotors.
new Over Voltage Protection Relay
new Idle Speed Valve
new Fuel Pump Relay and Fuel Filter

After a private Mercedes mechanic replaced with all 8 new Bosch Fuel Injectors, he reset the car to original timing and fixed the vacumn hose wrong routing by previous mechanic..... but the car still has a rough idle problems --- though the gas mileage has been improved to about 17 MPG in city driving.

Now he told me that the center intake manifold's 8 vacumn plenums needs tobe replaced -- if I want to fix this rough idle problem......Well, I think he should tackle the vacumn problem first before doing this fuel injector jobs, so I don't really trust his Mercedes skills ... Questions : Can I replace this plenums myself and if yes, can anybody give me any problem areas to watch for if I proceed to buy the parts from the Fast Lane ???

Thanks for reading this message. Regards.