I would check the OVP Even when they test fine, sometimes they are not from what I have read on this site.
I'm not a tech, but I understand your frustrations.
I would check for spark, if you smell fuel, then fuel must be getting through.
You said you just had a Tuneup, so I take it they replaced plugs, cap, wires, and rotor? They changed the Fuel pumps and an o2 sensor.
So I think your only other thing to check would be the OVP or one of the other units you took out and cleaned.
Did you do one at a time? Or did you just unplug a bunch of them and clean them all at the same time? If you took a bunch out are you sure you put them back in correctly?
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.