1999 Ford F-150 V6 4.2L: Fixing OBD-II Codes 0171, 0174, 0401, and 1408 with Shaking at Idle
My son owns a 1999 Ford F-150 V6 4.2L 2WD with 112,000 miles. Recently, the truck began shaking severely at idle and low speeds—similar to being about to stall—but does not actually stall. The Check Engine Light (CEL) has been on since purchase six months ago, but the vehicle had previously run fine. A diagnostic scan revealed OBD-II codes 0171 (Fuel Trim Bank 1 Too Lean), 0174 (Fuel Trim Bank 2 Too Lean), 0401 (Diesel Particulate Filter Efficiency Below Threshold), and 1408 (Oxygen Sensor Heater Circuit Malfunction). After clearing the codes, the shaking stopped temporarily. However, within a few days, the symptoms returned along with the reappearing codes. A local shop suggested a full repair package: removing and replacing the intake manifold ($500), replacing the EGR pressure sensor ($150), installing three new oxygen sensors ($300 total), and performing a fuel system tune-up ($200). The cost totals $1,600. However, after clearing the codes, the truck ran smoothly—so why did the issues return? Is this repair plan justified given that the vehicle previously operated normally without these parts being replaced?
I have a similar issue with my 1998 Ford F-150 4.2L. The truck shudders when first starting, which gradually resolves after driving for several minutes. I noticed intermittent misfires between 45 and 55 mph. Initially, the CEL indicated a coolant temperature sensor out of range—after replacing that sensor, the issue was resolved. However, recently the shudder has returned. I suspect carbon buildup in the throttle body, which I cleaned recently. I haven’t driven it yet to confirm if the problem is fixed. If I identify the root cause, I’ll share my findings here.