I have a 1991 pathfinder xe 4x4 173,000 miles, when it idles it sounds great but when you put it in gear and go it sounds like something with a valve like its not primed. Its not exhaust but the exhaust manifold gasket on the driver side has never been changed EVER!!! but if its not that then what do yall think it could be? And i bought some lucas oil stabilizer, is it a good idea to add this on the next oil change??? Or is that a sign that the manifold gasket is about to give in??? Please let me know, Thanks.