Hi,
It sounds really like a fault I had on my cinq last winter, Check the big electrical connector at the front of the engine bay. disconnect it (its got a sort of locking mechanism you have to push before it will separate) and make sure all of the pins are clean and not corroded, clean them all any way.
If it is the same as mine the intermittant fault keeps putting fault codes into the ECU which is why they cleared when you disconnected the ECU and got a good start, However when the bad connection breaks it starts loading fault codes again. hence the intermittant injection warning.
Hope this sorts it for you, but if not getting the codes read at a garage is the best bet.
Regards,
Michael
btw this is what Haynes says about resetting the ECU on a cinq
ECU Re-setting Instructions (extract from Haynes Manual)
Start the engine and run it until it has reached normal operating temperature. Keep the engine running until the cooling fan switches on, then off, then on again for a second time. If at any time during this warm-up procedure the engine stalls, restart it immediately.
Once the cooling fan switches on for the second time, switch the engine off and immediately disconnect the battery negative terminal. Leave the battery disconnected for approximately 45 seconds, then reconnect the negative terminal; this will reset the ECU memory.
Once the battery is reconnected, immediately start the engine and allow it to idle for approximately 2 minutes. If the engine stalls during these initial 2 minutes, disconnect the battery negative terminal again for a further 45 seconds, then restart the engine and allow it to idle for a further 2 minutes. Repeat this procedure as required until the engine has run for at least 2 minutes without stalling; the ECU is then reprogrammed sufficiently to allow the engine to run and idle smoothly. Note, however, that it will still take a few miles for the ECU to learn the optimum settings for all operating conditions.