sorry, re the map sensor, i was thinking it was the older type...map sensors on your model can only really be tested with a scanner with live data, or an oscilloscope...although still possibly at fault, not as common as the earlier type with the hose.
would be handy to have the engine code, which would be stamped on the right/front side of engine as you look at it from the front, just below the cylinder head....probably starts with a J
couple of tests you can do with a voltmeter
coolant temp sensor.
should be a 2 wire sensor, cant be specific about which wire is which, but easy enough to test.
with ignition on, engine cold, sensor plug connected
1 wire should be 0v, other should be approx 3.5v....any strong variation from that could point to a problem...the sensor voltage should gradually decrease as engine gets warmer,
if you can test it, let me know what reading you are getting
throttle position sensor
should be a 4 wire sensor, again, cant be specific about which wire etc
ignition on, sensor plug connected, engine temp irrelevent
1 wire should read 5v
2 wire should read 0v
3 wire should read approx 1v with throttle closed, approx 5v when throttle fully open [this maybe vise-versa)...as you gradually open throttle from closed to fully open, the voltage should rise ([or fall) gradually and smoothly without any jump to 0 or 5v in between....let me know the readings you get
4 wire, i believe, is the in built air temp sensor, hard to be specific with this, but air temp (within the manifold) at about 10 deg should read approx 3.5v..warmer the air, lower the voltage
with regards not setting a code if faulty
as an eg...the coolant sensor...if sensor fails it still might give a voltage within its parameters...lets say its supposed to read 1v when cold and 4v when hot...well it might read 3v when cold...makes engine difficult to start but wont log a code as the voltage is still within its expected range...think that makes sense...same could be said for a number of sensors
your problem could also be injector leakage, or pressure regulator problem...if you kitted up/confident in having a go, can give tips on how to test those
hope this helps