hi.
if you have a new coolant sensor then worth fitting BUT just make sure its the right one. in earlier 80' & 90's bosch jetronic injection cars (carlton,manta,senator) etc there were 2 variations that looked identical but one had a single element that had a circuit across the 2 terminals but not to the body and there was a type with 2 seperate elements that each had a circuit to earth.omega ones may not be like this anyway but worth mentioning as the wrong type fitted to a jetronic didnt work !just check wether yours has anypins circuit to earth and the same with your new one.chances are the old one is fine anyway. this sensor tells the ecu how hot the engine is .if in any doubt aboutthe new one then leave the old one in !.(the other brass one with the spade is for the temp guage and wont affect running in any way)
fuel pressure could do with checking just to eliminate that side of things.
other things to check ( probably mentioned before)
plugs ,leads,coil.
breathers,hoses,air hoses,vacuum connections,servo pipe,
throttle body (often gunged up !) dont play with any of the adjustments thou !
we have to assume the actual basic engine is physically ok as well. compression test ,cambelt/ alignment,.
just a few ideas.