Low & rough idle with intermittent stalling and no throttle response when warm

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!

 

reset ecu and report back. I believe the 03-04 have drive by wire issues so you might have to look into in depth.

 

Thanks Tony2018, I am planning on doing that after work. I figure with replacing the throttle body with no change I eliminated the 3 sensors for the drive by wire system. I also checked my crank sensor and it was good (they also rarely die according to a Toyota mechanic I spoke with).

 

Tony2018, I was able to reset the ecu last night. Drove to Lowes and back home (20 minutes roundtrip) with no issues. Drove to work this morning and so far no issues. I am still unsure if this resolved my issue, but I am assuming it will happen this afternoon in hot rush hour traffic if it were to happen at all so I will report back.

 

Have you been keeping up basic maintenance, like spark plugs, fuel filter, air filter, clean the maf

 

Basic maintenance has kept my old mans 98 single cab going forever. Kinda hard for me to tell you what it is because I seriously never encountered any issues.

 

Hey Sperrunner,

Yes sir, plugs and wires replaced about 2 years ago - OEM, fuel filter replaced 3 months ago with new fuel line, air filter replaced last year and the MAF is brand spanking new.

 

new maf? oh an ecu def needed a reset.

 

Ha yeah, that was s rookie move on my part. I completely forgot to do that. Hoping that's what the issue was all along. Still wondering why it didn't throw a code?

 

So far no issues. Drove fine yesterday and this morning. Still keeping my fingers crossed. I have a trip from Tennessee to Moab, Utah to Auray, Colorado and back planned in about 2 months with many miles being off road. Trying to make sure everything is in tip top shape before I hit the road! I am bringing spare belts, spark plugs and wires, and fluids with me. I am planning on having the transmission drained and filled (hesitant and doing a full on flush), brake fluid change, and diff fluids. Not sure what else I should be checking.

 

I was having the same issue in my 2001 V6 TRD. No codes or CEL. The truck ran terribly and had the same issues you're experiencing. Every sensor or other part I replaced seemed to fix it immediately, but after driving a few hours the problem came back. I replaced the plugs and wires, fuel and air filters, MAF, IAC, cleaned the TPS and the problem still came back and still no CEL.

Finally I replaced the TPS, and the problem went away. Try replacing the TPS if your problem comes up again.

 

Interesting post here. I have similar vehicle. Gotta ask- what do you mean "drive by wire" yeah there is a throttle cable. I am not sure what is going on here except that you had a crapped up throttle body and crapped up MAF that were fixed by replacement. Interested to see if there is anything else that can cause this and eager to learn....

 

Toyota ECTS-i drive by wire system. I had no clue I had it till I started troubleshooting and was wondering why I had 3 sensors on my TB. The crap part is if in fact your TPS goes bad, good luck finding JUST the sensor. Toyota dealers only sell the ENTIRE TB...and for over $800+. I found one on eBay and swapped it out by it didn't resolve my issue. So far it appears my issue was from a bad MAF sensor. Knock on wood anyways.

 

Holly crap . there is alot to the throttle body. I've had mine off to clean it, but did not take it a part. Very interesting and thanks for schematics. I do have something to suggest: I heard that the throttle position sensor can get crapped up on the electrical wiper section. Opening and closing the throttle body manually (not with the engine on) a bunch of times (50 I heard) times cleans it up and restores its responsiveness. Looking at the schematic more closely, I don't thing mine has that throttle control motor. Just a cable from the pedal. Mine is 2004 V6 3.5 5 speed manual...

 

I’m under the impression all 2003-2004 V6 models have the drive by wire system. Check and see if you have electrical connectors on the backside of your tb. You may surprised! I have a throttle cable too but I believe after a point the throttle motor takes over and operates the butterfly valve.

 

So just to report; after resetting the ECU last week I have had no further issues. I believe my throttle response is much smoother but more importantly my mpgs have risen slightly to where I am getting 15.4 mpg around town which is better than new. No complaints here!

 

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.

 

Injectors?

 

Thought about that too, KGW, but wouldn't make sense that it would only occur when I've stopped at a light or whatnot after the truck is warmed up and my fuel pressure was measured at 43psi last week. Also, my gas mileage is 15 city which is spec for rolling off the factory floor.
Anyone else with ideas?

 

Your throttle position sensor might not be advanced enough