Fuel useage/100km

[charzy]

Hi everyone
A question that I believe is easily answerable but I'm awful with cars. I'm hoping this will be a quick fix.
Dad asked to have a look at the car (subaru liberty my09 spec b). He flips the bonnet, fiddles around when I'm not looking (Serviced 3 weeks ago). I find out he checked the oil and other things when I told him specifically not to, and he may have tampered with something superficially.
Soon afterwards when I'm driving I find the drive is not as smooth and the fuel usage indicator shows around 25-35litres/100 when I'm cruising at 60kkn, revving at ~ 1500-2000.
If I step on the gas, it'll go the other way i.e. 6-7litres/100km.
Any idea if somethings been knocked loose/hasn't been placed back properly?
Thanks in advance.
Char

[HardwareBoB]

He has probably knocked out a vacuum line creating a vacuum leak. Check all the vacuum hoses.

.. Then let your dad know he's only allowed to look at the car under supervision from now on! Attach one of these signs:

ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS AUTOMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.

[charzy]

I'll consult my manual and have a look tonight to check the lines.
Am I just making sure they're all sealed and tight?

Had a drive and can't even hit the turbo.

[GONEWALKABOUT]

hahaha thats a top effort by your old man!