ok so i just got this POS cavy for free for my summer car. When i first got it, the oil pressure gauge was all the way up, above the markings. It ran fine for a while, untill i had it running on idol for a while then put it in gear, and it stalled. Now, everytime i try to put my car in gear it stalls. Ive replaced a number of things on my car, but i can't figure out why it is happening. The wierd thing is though that when i put the car in gear, the oil pressure gauge goes back to normal, but stalls right after that.

Im really confused an i can use all the help and suggestions i can get. Thanks much