raptor510

Hello all,

Frequent lurker with a strange issue I'm really hoping to get some help with. I will be as short as possible.

2004 Tacoma TRD V6 with 180k miles. Bought 2 years ago as a second vehicle. Driven 2-3 days a week. Fully maintained. New plugs and wires a year ago with OEM parts. No other issues.

About a year ago I pushed on the gas pedal after coasting down a road and nothing happened. Engine was still running but no acceleration. A few seconds later throttle came back and truck drove normally. I'd read on here about the TPS becoming "dirty" and that pushing the gas pedal 100 times will "clean" it. Did so and didn't happen again till this past spring. Did the pedal thing again and no issue till 3 weeks ago. This time it was worse in the sense that as the throttle came back online acceleration was rough like the engine was stumbling or hesitating. Over the next few days it progressed to the extent that the truck would begin idling very low and rough when stopped and eventually die. Throughout all of this the CEL never showed it's ugly face and when I scanned for codes none were pending or stored,

I read on Yotatech about the TPS and thought I would replace mine only to discover I have the drive by wire system and the stupid sensor is not available without buying the entire throttle body. Bought one on eBay and swapped it out. No difference. Cleaned my original very well and put it back one and that made no difference. Thought perhaps my MAF was dirty so I cleaned it and that made no difference, Bought a new Denso MAF and installed it and that made no difference. I was out of ideas so i took it to a shop where some friends work. They thought it may be a fuel issue so they hooked up gauges and nope, fuel line pressure was 42-43psi. No problem there, I picked up my truck abd drove it that night and didn't have an issue. Drove it the next 2 days with no issue. Parked it for a day and drove my car. This morning drove it to work and no problems until I parked. I put it in park and the truck did the same rough idle for a few seconds then smoothed out.

I am stumped and so are my mechanic friends. The ONLY thing i can come up with is that my MAF was in fact bad, but I'd forgotten to reset the ECU after swapping it...so maybe the ECU is still learning or whatnot?

Hope you all can help me out!

raptor510

Nobody has any insight on this?

tantacoma

What about the 'pedal position sensor' ?
I'm guessing that it is a variable resister. Can you test that?

raptor510

Hey Rick,

Yeah I thought the same thing, but that sensoir, along with 2 others, are all part of the throttle body I swapped out and made no difference.

So far I've ruled out the throttle and it's associated 3 sensors, crank position sensor, MAF sensor, and fuel pump.

I reset the ecu last night for good measure and will see what happens.

Totally out of ideas at this point!

raptor510

Reset the ECU 2 nights ago and have driven her for a couple days with no issues. I am still keeping my fingers crossed. I am going on a very long road trip from Tennessee to Utah and Colorado in a couple months with many miles off road through high mountain passes and I need to have my rig in tip top shape. You guys have any checklists of spares and fluids to take with me and what maintenance I should take care of before I leave?

fierohink

raptor510

So just wanted to report in case people were still interested. After resetting my ECU I have not had the issue again. Hoping that's all that it was!

raptor510

And so I jinxed myself.
Drove the truck this morning and while I was stopped at a light the engine began idling low and rough again then stalled. Fortunately I was able to restart it and get to work. Once I parked she briefly lowered rpms while idling then straightened herself out.
I am totally stumped and at my wits end. I have a very long trip planned soon and cannot be dealing with this on a 4000 mile trip.
Does anyone else have any ideas? No codes, no performance indicators, ruled out all the sensors on the TB, ruled out fuel issue, and replaced the MAF.

fierohink

You say you "ruled out all the sensors on the TB, ruled out fuel issue, and replaced MAF". How did you rule out the fuel issue? Have you done diagnostics while the truck was performing poorly? Ideally you need a full spectrum scanner to run see realtime fuel trims and sensor data outputs. The FSM has a lot of specific information in the flowcharts for customer complaints. Like I said before about my own injectors, I had a hunch that that was the culprit, and after running a diagnostic scan I could see the ECU trying to flood the engine with huge fuel trim numbers while 2 of the injectors weren't firing. This all occurred after heat soak. Not on start-up, not on short trips, but after all the components got up to operating temp for a while. Sometimes as long as 30-45 minutes of driving if I was moving and things were staying cool.

The FSM should have specs for all the sensors. Some you test voltage across, some you test impedance, etc. You will need to do these tests when your truck isn't running correctly.

raptor510

Hey Fierohink, i suppose I should have said my mechanic ruled out those things. He said the fuel pressure on the rail before the injectors was steady at 43psi and that the injectors were firing, but he did not mention how he came to that conclusion.
I drove yesterday and just for the hell of it I hooked up my Bluetooth OBD2 scanner and fired up my DashCommand app. It did begin to idle roughly when leaving work so I checked for codes and finally 1 then 2 showed up as pending codes. P0171 and P0305. I’m suspecting I have a vacuum or intake leak somewhere past the MAF??? I know unmetered air can cause misfires just curious as to why it’s only one cylinder??

fierohink

raptor510

So took my truck to the shop yesterday. They found no intake leaks anywhere and said hoses were all good. Checked pcv valve and it was good. They hooked it up to their Toyota scanner and said all the fuel trims were good and found no other issues. Unfortunately, it never stumbled or acted up for them on their test drive or while it was idling for quite a long time. Their only suspicion is the injector on cylinder #5 that originally through a pending code for me. They recommended a stout fuel treatment dose of 3 x 6oz bottles of Lucas and told me to drive through that tank of gas and add some more Lucas to the following tank to see if possibly clears up.
Fierohink, you may right about the injector going bad. I didn't have time to swap coil packs around but may try that this evening.
Should I wait a few weeks and see what happens or assume the injector is going bad and swap it out? If I replace it, should I go ahead and do them all?

fierohink

Soumipukuu

I'm on the bad injector idea, mine showed correct fp at all times but one was leaking, would idle like crap and had crappy acceleration.

Soumipukuu

And no cel showed up either

Thommo Thompson

the original problem was described as total power loss for a few seconds on acceleration....
DC motors such as those in fuel pumps can be quite temperamental, and if one cylinder is slightly down on compression then that will be the one that missfires in the event of a continuous state of slightly lower than ideal fuel pressure.
The times u lost power completely may have been a symptom of the fuel presssure being substantially lower than needed for a brief moment.

I would have the fuel pressure tested during a few hard dyno runs so long as it isnt too expensive a test.