2006 Renault Megan Dynamique Sport Tourer. The tailgate popping open on its own

check glove box?

Whatever the cause, the cylinder head will have to come off, so you are looking at some engine rebuilding. If the bottom end of the engine is still good (the pistons and piston rings and bearings on the crankshaft), you might get by with a head and valve job. Not cheap, but cheaper than a complete rebuild. Have your mechanic do a leakdown test before teardown, to pinpoint the reason for no compression in that cylinder.

go to a breakers hard for a spring

Reasons for heavy fuel comsumsion:
Engine tempreature running cold
Injector leak down
Fuel pressure regulator diaphram leaking
Fuel return line blocked
Fuel pump creating way more pressure
Transmission slipping
TMP engine tempreature grounded
O2 sensor not going into closed loope.

it will be in the fuse panel it might be on with other things like das lights or something like that or it may be by its self

Probably the switch you press to open the tailgate

call scrapyard ,its a renault remember ,encrypted software DEALER ONLY hope you can lay the golden egg for so he can spend it all in las vegas and a condo in florida

What sort of noise? Could it be the winscreen wiper motor?

gearbox needs changed or clutch release bearing

the carb needs cleaning, thats what it was on mine, i thought it was spark plugs but took it back to main dealer and they fixed it but cost £££