A vehicle with a lean condition at idle but normal fuel trim at higher RPMs likely has:

A vehicle exhibiting a lean condition at idle but showing normal fuel trim at higher RPMs suggests that there is an air leak affecting the air-fuel mixture at lower engine speeds. The scenario described indicates that the vehicle has enough fuel at higher RPMs to maintain a proper mixture, but a vacuum leak or an issue drawing in excess air at idle is causing a lean condition in that state.

The presence of a leaking intake manifold gasket fits this description well. At idle, when the engine is drawing a smaller volume of air, an additional source of air entering the combustion chamber due to a leak in the intake manifold will lean out the mixture. However, as the engine accelerates and RPMs increase, the increased airflow could compensate for the leak, resulting in a normal fuel trim.

Other options such as clogged fuel injectors or a faulty fuel pump would likely cause fuel delivery problems at both idle and higher RPMs, thus not aligning with the symptoms described. Similarly, a faulty oxygen sensor could lead to incorrect readings that affect fuel trims, but it wouldn’t specifically cause a situation where higher RPMs show normal fuel conditions while idle remains lean. Thus, the leaking intake manifold gasket is the most logical explanation for the symptoms observed in this scenario.