3.4l Hesitation/Losing Power

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.

 

Try cleaning the MAF if you haven't done that yet.

 

^^ MAF
Clean IAC
Clean EGR if applicable
Don't know the resistance to check with a voltmeter but do some research and check throttle position sensor

 

Without being there and looking at everything, my first gut reaction is rats nibbled on some wires (any signs of rat poop under the hood?) because it sat but it could be almost anything. My second suspicion suspecting that your fuel pump is questionable because you state that an immediate opening of the throttle causes a miss, classic issue of a fuel pump failing. If you live in a reasonably sized city there should be a auto parts store that can check codes for you for free. Just because the CEL isnt on does not mean that there isnt any information to be gathered by putting a scanner on it. While at the parts store ask if the scanner that they will be using has live data provisions and the capability to check for pending issues. Pending issues are issues where there is a problem but it hasnt yet risen to the point of setting off the CEL... a certain # of misfires in a given period is a good example. What you are wanting to look at are the long term and short term fuel trims. Ideally, both should be around 0 but 5 to 8 percent either side of zero is "acceptable". A negative number means that fuel is being taken away and a positive number means that fuel is being added. Let her idle for a minute and watch the fuel trims then slowly increase the engine speed and watch the trims. If they start to rise and hold steady above 20% this is a good indication that the fuel pump cant keep up with the pressure and volume demand and the PCM is holding the injectors open for a longer and longer period. To confirm you would have to put a fuel pressure gauge on it and snap the throttle a few times to see just how far it drops in pressure.

I feel your pain about $120 hr to have a spin at the technician wheel.

 

Check the coils with an ohm meter too. Sounds like electrical for sure. Check Chassis ground, and all of your battery and terminal connections at the fuse box. Fuel pump is certainly a possibility as well. Glam is spot on, check all wiring looms for chewing. Fuel trims will be a huge plus.... https://www.autoserviceprofessional...-works-and-how-to-make-it-work-for-you?Page=1

 

When was the last fuel filter change??

A lack of fuel miss seldom trips a code where a electrical miss will.

stepping on the throttle is just giving the engine more air

I like the rodent chewed wires as well

 

Also make sure you don't have one or more loose ground wires. There are a few in various places.

Battery terminals tight and clean?

 

I remember a thread a while back about a similar issue. OP tried EVERYTHING. Turned out to be a clogged catalytic converter.

 

It sounds very similar to an issue I'm having. When it loses power does it act like the engine died or was turned off (check tach and it's idling), push the pedal down and absolutely nothing happens, but hold it down then all of a sudden it takes off? Sounds like the 03-04 non serviceable TPS issue. Toyota will only service the entire throttle body. Search 2004 tps for a long list of posts.
I can't decide what to do about mine but leaning towards the $700 TB from Toyota parts deals.
I would like to hear from someone that has replaced the TPS with one of the foreign sourced parts regarding installation, adjustment and operation.

 

Was this issue ever solved? I had a simmiliar issue, but no miss. Also bought truck with ~160kmiles. 97 3.4 4wd 5sp. It had 380 some gears so i went to 4:10 as i was runnin 31s or 265/75 16.. did plugs and t-belt, and all the oils trans, axles, etc.. but the symtom was the truck ran fine. Low end an mid range power was fine. Top end it seemed to fall on its face. Down 15 maybe 20 hp wot...it kinda felt like a 3.0l pickup.. if you drove like an old man youd never know. But no missing. Ive had other 3.4's an knew it was down on power above say 3200 rpm. I had began to think the I heads needed attention or injectors maybe. Then kinda forgot about it. Ended up replacing the plug wires when i did the valve covers and boom... top end power is back.. they were original sumitomo date coded 1996.. im gunna check the resistance on wires just to see what was going on with em exactly.. the truck was garage kept an the original wires looked so good i assumed they had been replaced.. never wud have thought it was the wires with how it acted...

 

I ohmed the wires out ans sure enough, two were 20 to 30k ohms resistance the 3rd was 185k ohms.. shud be around 15000 for a 3 foot wire..