Oil light on warm idle????

i have 5w-30 valvoline max life, i live in utah... right now its pretty cold but during the day when the sun is out its not too bad... i have a mini me in the car with a sohc zc block... i had to take the oil pressure nozzle out of the block because every web site i looked at said it needed to come out because the d16z6 head already has its oil pressure nozzle thing and with the pressure nozzle in the block the pressure would be to high and vtec wouldnt work... wouldnt really matter in my case tho... my vtec doesnt work... also i just barely got this block from japan auto 2 weeks ago... and i think a rod bearing is starting to go already..... could that be because of the oil light issue? it only does it when it idles... i have no leaks at all and theres plenty of oil in the motor

also the oil is still very clean.... and is it ok to run any other oil than 5w-30 in the sohc vtec?... when i changed the oil i left the old filter on that had some synthetic oil in it and i put regular oil in... could that have caused it? this filter only had about 20 miles on it

jus tryin to keep this on the first page... i could really use some answers....