front engine seal replacement? spark plug firing sensor? dont know whats wrong?

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driving around town this week the engine started running rough when at stoplights and idling. It was fine when driving and accelerating then yesterday when I got a stop light it felt like the engine wanted to die and suddenly the check engine light came on. I had thought I needed to get spark plugs replaced but I had the code read and the guy told me it was maybe the front engine seal leaking because there's oil all over the timing belt and maybe getting on the spark plugs causing misfires. Or maybe its some kind of spark plug sensor... I don't know... Has anyone had problems like this before? Please help..... My husband and I are worried this is going to cost a lot of money...Also the air conditioner has been giving me a few problems....I dont want to but maybe its time to trade it in for another car... :(