The P2187 OBD-II fault code means the vehicle's on-board computer has detected a lean fuel mixture at an idle in either Bank 1 or Bank 2 (the side of the engine with the corresponding number on the cylinder, if applicable). A lean fuel mixture means there is an excess of air and a shortage of fuel.

check your fuel trims at idle and again at highway speed.   If they are the same, then you have a fuel delivery issue, ie  low fuel pressure or clogged injectors.   If trims are much higher at idle, then you have an intake leak.   Could be as simple as a stuck open PCV valve, unplugged/split hose, or a blown brake booster.   Smoke test is the quickest way to find that vacuum leak.