Stuttering Navigator head scratcher
2004 Navigator 5.4 RWD with 118Kmi.
The SUV has been intermittently struggling with acceleration from time to time and occasionally shutting off at stop lights. Since the problem has gotten worse, I brought it to the mechanic due to this and a fuel smell where I am inclined to believe the two issues are separate.
Originally the mechanic replaced the gas tank due to small cracks found in the tanks connectors and also said the evap code was due to 2 charcoal canisters in the evap system that should be replaced but now that the tank is replaced I decided to hold off on replacing the canisters since it does not smell as bad as it once did and the mechanic said the evap issue has nothing to do with the other issue I am having.
Although I can sometimes feel the issue at slower speeds, it has major hesitations trying to accelerate after idling above 45mph. For instance, when driving on the highway and trying to pass someone the vehicle starts to spurt and sputter and hesitate to accelerate. If I lay into the throttle more, the issue becomes more pronounced.
The mechanic said he saw some misfires on his scanner and recommended changing the spark plugs. A week and $280 later I briefly test drove the vehicle and did not notice any issues but I did not try getting up to highway speeds. The following day, I took it out and it stalled out 3 times at a stoplight a mile from home, I noticed the RPMs sounding like they were struggling to stay consistent and the issue of difficulty during acceleration was back, especially ay higher speeds.
I immediately brought it to the mechanic and he looked really stumped, I recommended we go on a test drive together so he could see exactly what I feel to be the issue and plan on doing that in the morning but I feel like I just spent $280 unnecessarily and that most mechanics are going to have me spending money on their guesses. Hopefully the forum has some knowledge on the issues of this engine, where the issues are intermittent at idil/slow speeds. Thanks for your help!