i had an issue like that with my p71 when i was on a trip back up north. could be as simple as needing to change ur spark plugs, i bought an old police cruiser and they had just used hodge podged spark plugs with different gap sizes...screwed things up a bit...or if you're unlucky replacing your coil packs which can be a bit pricey. pcv valve can bet tested to see if it's good or bad but like spark plugs that's something you should change at least every 30k. can't hurt to replace either of those | 
