Cold start valve will not be activated unless the outside temp is below 60 F. So you should be OK there.
Since you have a manual transmission, were ever able to start it using the clutch and gear? (Ignition On, 1 or nd gear, downhill, let clutch go?)
Also, just in case, you might want to read out the output on pin 3 of the diagnostic port. Maybe for some reason you air/fuel ratio have changed.
'88 Benz 420 SEL
'79 Porsche 911SC ('87 Carrera Engine)
'00 BMW 540 Sports Package
'99 Land Rover Discovery
86 300E - Manual (sold)
88 260E (sold)
84 944 (sold)