Truck: 2003 3.4l 4x4 TRD xtracab, manual. 187,777 miles. I bought at 172k.
I recently moved to a new area where I initially needed to drive my truck much less often. About 6 months ago I let my truck sit for about 10 days without even starting it up. It started with very little hesitation, but immediately started acting like it was missing on 1-2 cylinders; the whole truck was shaking like a bastard. After about 5 minutes it was idling fine, but it would randomly lose power when driving at a constant speed for 1-3 seconds (not electrical, it acted like I let off the throttle). It seemed to happen predictably (75% of the time) when I would let off the throttle for a second then push it down again, a.k.a when shifting gears. After about 45 minutes it started driving like nothing happened.
Initially this problem correlated to how long I let the truck sit. If it sat for more than 6 or so days it would repeat the same set of symptoms, but if I drove it regularly the symptoms went away.
Fast forward to today: I’m driving the truck almost every day for work now and I’m randomly losing power no matter how much I drive it. I no longer have any rough idle at start, but I never let it sit for more than 2 days. The power loss can be a little blip you hardly notice or a total loss of power for a few seconds. The present iteration of the problem is very sporadic: I can drive 100 miles on the highway and have no power loss, but when I go to pull into the gas station at the end of those miles I’m frantically pumping the throttle trying to get it to do anything at all. I seem to be able to cause the symptoms if I hammer down on the throttle then suddenly let off, then push on the throttle again. I can lose power for up to five seconds.
Sometimes the power will come back gradually as I pump the throttle: First pump nothing, second pump nearly nothing, third pump a lil something, fourth pump and we’re off! If the throttle is unresponsive and I simply hammer down, nothing (AT ALL) happens for about 3 or so seconds, then it comes back to itself and I’m peeling off.
When the truck is running well I have no power issues whatsoever.
I have no check engine codes in the computer and the light has never come on.
Things I have done: changed spark plugs, inspected cables for obvious housing issues, replaced fuel filter, replaced air filter, run Seafoam through the system a few times. My mechanic is stumped. Initially he believed I might have a cracked head/bad head gasket leaking into one of my cylinders causing it to misfire, but after a leakdown test he ruled that out. For some shitty reason it ran perfectly for him and didn’t show any symptoms for about a week after, but now exhibits symptoms nearly every day. BUT NOT ALL DAYS! I’m not leaking coolant and I lose about 1/2 qt of oil between changes.
Because it’s so sporadic I’m leaning toward an issue with the fuel pump or an electrical issue related to ignition. Anyone have any experience with this? I couldn’t find anything on the forums. Any leads would be greatly appreciated, leaving it at the mechanic for them to screw around at $120/hr and come up with nothing really isn’t working for me.