My 1994 E320 mercedes check engine light is on , but no diagnostics available, what now?

First things first, check the ovp relay. It's on the bulkhead under the bonnet, square silver can, clear plastic lid wiv a fuse in the top. If that's ok there's a little black box just behind the headlight wiv 2 round plugs which fail often. Could also be simply a fuel pump broken down. When you turn the key to auxiliary do you hear the pump hiss? Fuel head could be on its way out, that's the silver thing on top of the inlet manifold with all the pipes coming out of it. Also check your spark plug leads, they tend to split and when that happens they lose power which causes the plug to produce a weak spark. Check the dizzy cap for cracks, they notoriously brittle. The bit under the fuel head, the bit that's half metal half rubber, has a couple of air hoses going to the underneath of it, check these are still attatched and don't have any splits. Good luck.

The average corner garage's code reader will only read OBD codes which are for emissions related faults. You'll have to go to an MB shop to get proper diagnoses. Sounds like, however, you have a "tired" MAF sensor which will cause thoses exact symptoms.

before you take it to the stealers, if you have the codes picked up on the machine, take a look here: http://www.obd-codes.com/trouble_codes/