1998 Ford F150 P0174 and P0302/P0303 Codes: Rough Idle That Fluctuates When Engine Light Comes On
Hi, I own a 1998 Ford F150 with a V6 engine. Recently, I've been experiencing intermittent rough idling and engine misfires, accompanied by three diagnostic trouble codes: P0174 (System Too Lean on Bank 2), P0302 (Cylinder 2 Misfire), and P0303 (Cylinder 3 Misfire). The truck runs smoothly when the check engine light is off, but as soon as the light comes back on, the idle becomes very rough—sometimes even causing a noticeable misfire. I've already replaced the coil pack, spark plugs, spark plug wires, and fuel filter. Despite these efforts, the engine light remains intermittent and the misfire persists. I'm seeking advice on how to resolve this issue permanently. Thanks in advance for any insights or troubleshooting tips! Charles
The symptoms—especially the fluctuating rough idle and misfires on Bank 2—suggest possible intake gasket leaks on bank 2. If you have access to OBD-II scan tools, check the oxygen sensor readings and fuel trim values during poor running conditions. Does the issue occur only at idle or under partial throttle? Also, clogged EGR ports in specific cylinders are common; try disconnecting the vacuum line from the EGR valve—this can help determine if the problem is related to part-throttle misfires. Note: This test applies primarily when skipping occurs during partial load. Additionally, inspect the PCV elbow under the throttle body—it may be cracked or split, though this typically causes P0171 and P0174 codes rather than P0302/P0303.