I purchased this '03 Base in '09 with 80k miles. It now has 92k. I've never seen the engine until today. Yesterday, it through the 171 and 174 codes. After a few hours of searching, a failing AOS seemed to be the culprit in many of these cases. The car runs fine, no problems with the idle, no smoke, but the oil cap is very hard to remove - in fact, I couldn't remove it with the engine running. I decided to take a peak to see if there were any obvious signs, loose hose, etc. Was surprised to see both sides of the intake coated in oily gunk. Any ideas where this came from or what I should check first?
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