Funny Idle/oil light after major repair

rough
mitsubishi
oil
lights
galant

#1

I had the timing belt go on my car while it was going. being an interference engine, it decided to take the intake valves with it



about fifteen hundred bucks lighter (valves, belt, water pump), i get the car back to see a flickering oil light a few miles from the shop at stoplights.



When i take it back in, they look at it for a while, and then change the oil to something really thick like a 10w-50 and tell me it’s because the original stuff they used was too thin.(The spec for the car was something like 5w-30, which it was running fine before.)



A few days later, the car is still idles funny (and has cut out, mid turn into a parking space 2 times) and the oil light will still flicker at random while the car is stopped.



I’m planning to take it back in, but seeing if anyone has any suggestion or thoughts on the possible cause(s)?