Accidentally got alot of water in oil filler cap and ran it. the car shakes now. is there anything i can do

Check your oil filler cap for whitish froth , if there is your head gasket has gone or worse scenario cracked block .

how much is a little and how does anyone confuse a gas filler neck with an oil fill cap, they are in two completely different locations. if you haven't put in more than a cup of gas then it will burn off and not cause a problem therefore you won`t have to do anything but drive it. if its more then the drain plug is on the bottom of the OIL pan and you will or should change the oil and the filter as the gas will be in the filter as well.

My sympathies, unless someone has accidentally poured water into the oil filler cap, you have a blown cylinder head gasket and the engine will require at least a top overhaul. This is a job for a qualified or at least an experienced person.

may be the head gasket, check the oil filler cap for lime creamy deposit & if you can see the water throught the top up filler cap a red/blue discolouration on the top layer of water shows if oil is getting into the water system. either of those two test's mean's the head gasket need's changing, if not then change the thermostat, they usually stick closed from starting & cook the engine in minutes but you never know, anything in the cooling system could be causing this, a blockage or the water pump......
Hard problem to diagnose, I'd have to be there, but hope that help's..

First find exactly where the water comes from.
broken hose or hole in radiator - if no leaks here then :-
broken / loose drive belt to water pump - sign is no heat to internal heater
thermostat stuck - heats up and overheats quickly. water from exits rad cap area
also check radiator cap - should be sprung to contain water under pressure, usually these are very reliable

check oil filler cap [inside of] - should be oily and grey/black If it has a covering of what looks like soft brown aireated jelly then possibly hear gasket or other internal engine leak between water & oil ways. The excess pressure from engine will force water out of rad cap area . A compression test with variable readings for between cylinders will confirm this. Hope its not this. It's expensive

mmmm maybe a head gasket check for creamy substance under oil filler cap .check water bubbles when running ,look in radiator

Sounds like you have blown the head gasket when it got overheated.. The white stuff in the oil cap is emusified oil, a bit like mayonnaise.
You will almost certainly need to replace head gasket and service the cylinder head.

Carry out sa compression check wet and dry. Then i'm affraid its head off time.

did you run a compression check? if so and its good then you have a blockage in the water jacket
if not then you have a head gasket leaking

http://www.volvoforumsrepairs.org.uk/800Repairs/inmanpcv.htm look at all your hoses i changed all mine for 4mm silicon hose and found some split /blocked that fixed the back pressure problem dont drill your cap that aint going to fix it it just lets oil run every where .