Tune Up Help/Recommendations

[Luciendar21]

My 00' Limited has been throwing intermittent P0171 (Running Lean) errors and some very occasional misfires. Timing belt was done in September by a reputable shop, and the P0171 began occurring even before that, I'm thinking time for a bit of a tuneup. Planning on:

• Spark Plugs
• Spark Plug Wires
• Mass Airflow Sensor
• Fuel Filter

Any advice on what I should get for each, or anything else I should do while I'm at it?

Spark plugs I have NGK BKR5EKPB-11 in my cart, is that right?
Spark plug wires I have NGK TE66 in my cart.
MAF I have already purchased Denso 197-6020.
Fuel filter I have Genuine Toyota 23300-62030 in my cart.

 

[Luciendar21]

I should also note that in addition to the codes and the misfires, it feels very down on power (it's not the quickest beast in the world to begin with) and when it misfires it refuses to misfire altogether.

The first several times the misfires occurred it was when there was poor weather. I suspect that the aftermarket cold air intake and spacer put on by the previous owner is allowing water to enter the intake. I plan to restore the factory intake the next time I am back at my home (a few months away) where it is stored, but in the meantime I'll continue to operate with this aftermarket intake.

 

[Acorn22]

4runners like NKG and Denso plugs and wires, and for a fuel filter I would just shop around on Rockauto for one. As for the lack of power, I would clean your throttle body and intake, and a new MAF should help for sure, along with a new PCV valve. Also make sure your throttle cable is tightened.

I ran a can of seafoam through my intake from the PCV hose and that helped clean a bunch of garbage out and made my runner more responsive, but some people will argue whether or not to use that stuff.

 

[Rock_Rat]

My 00' Limited has been throwing intermittent P0171 (Running Lean) errors and some very occasional misfires. Timing belt was done in September by a reputable shop, and the P0171 began occurring even before that, I'm thinking time for a bit of a tuneup. Planning on:

• Spark Plugs
• Spark Plug Wires
• Mass Airflow Sensor
• Fuel Filter

Any advice on what I should get for each, or anything else I should do while I'm at it?

Spark plugs I have NGK BKR5EKPB-11 in my cart, is that right?
Spark plug wires I have NGK TE66 in my cart.
MAF I have already purchased Denso 197-6020.
Fuel filter I have Genuine Toyota 23300-62030 in my cart.

You're cart looks fine.

Run 92 octane to minimize the pinging until you find the problem. Examine all of your hoses for possible cracks or wear.

I had an intermittent 0171 a while back and it ended up being my plugs. If that doesn't fix it, it could be your MAF.

If/when you replace the MAF, be careful not to strip or drop the tiny Phillips head screws. Place a large towel under the air box, or remove the air box.

Here's a start...

 

[wemslie97]

O2 sensors done? They can cause lean/rich issues also I believe.

 

[19963.4lsr5]

Any air leaks between the MAF sensor and the throttle body can produce it. The pre cat O2 sensor produces the 171 code. It could be fuel flow, a sensor not providing correct info to the ECU. I'd look at fuel pressure, the MAF sensor or air leaks between the MAF sensor and the throttle body.


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[BamaDrewski]

How long has it been since you replaced both 02 sensors? If it has been awhile, it can make a big difference. Just disconnect the battery for the ECU to reset and "start anew" after doing this.

One other thing that might feel like a "misfire" is often the TPS (Throttle Position Sensor). I have had to replace mine 4 times in the 13 years I have owned my rig. RECOMMENDATION: ONLY USE OEM TPS SENSOR - NOT AFTERMARKET!

 

[fblainen11]

Not sure how much MAF sensors cost, but I'd start with new spark plugs and wires and see what that gets you.

 

[gamefreakgc]

My 00' Limited has been throwing intermittent P0171 (Running Lean) errors and some very occasional misfires. Timing belt was done in September by a reputable shop, and the P0171 began occurring even before that, I'm thinking time for a bit of a tuneup. Planning on:

• Spark Plugs
• Spark Plug Wires
• Mass Airflow Sensor
• Fuel Filter

Any advice on what I should get for each, or anything else I should do while I'm at it?

Spark plugs I have NGK BKR5EKPB-11 in my cart, is that right?
Spark plug wires I have NGK TE66 in my cart.
MAF I have already purchased Denso 197-6020.
Fuel filter I have Genuine Toyota 23300-62030 in my cart.

Not to be a downer but most likely you are still going to have the code. The most common cause of P0171 is a vacuum leak, here's a great video on how to check. It's simple and free:

<iframe width="560" height="315" src="https://www.youtube.com/embed/9CPqbaSgcok?rel=0" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

Second most likely cause is a bad upstream O2 sensor. They will wear out over time and can fail, but the heater circuit still works so you don't get that second code pointing to the O2 sensors.

Third most likely is the MAF sensor but it normally just needs to be cleaned, not replaced. But since you already bought one, go ahead and use it.

 

[Luciendar21]

Any air leaks between the MAF sensor and the throttle body can produce it. The pre cat O2 sensor produces the 171 code. It could be fuel flow, a sensor not providing correct info to the ECU. I'd look at fuel pressure, the MAF sensor or air leaks between the MAF sensor and the throttle body.

There's a Cold Air Intake in place from the previous owner. I'm planning to swap back to the factory intake (which I have in a garage at my house where I am not living presently), but it'll have to wait until I'm next home (I'm not buying a second one just because I can't get to the one I have at home). I've always suspected something is screwed up with this intake (AEM-21-8402DC), which also has a Throttle Body Spacer (I believe it's an AIRAID 510-502).

 

[Luciendar21]

Not sure how much MAF sensors cost, but I'd start with new spark plugs and wires and see what that gets you.

MAF is the one thing I've already purchased (went with my gut having had very similar issues with an EJ205 in an '02 WRX that were caused by the MAF). Not sure it makes much sense not to put it in where it's already sitting behind the driver's seat.

 

[Luciendar21]

Run 92 octane to minimize the pinging until you find the problem. Examine all of your hoses for possible cracks or wear.

Been running 93 octane since the misfires began to happen and ran some fuel system cleaner through the lines since I couldn't get to fuel filter/injectors anytime soon. Definitely helped and I haven't seen misfires in a while.

If/when you replace the MAF, be careful not to strip or drop the tiny Phillips head screws. Place a large towel under the air box, or remove the air box.

Aftermarket Cold Air Intake, I haven't swapped the MAF despite having the part for the past two months because the intake actually has the MAF on the bottom in just about the least accessible spot.

 

[Luciendar21]

O2 sensors done? They can cause lean/rich issues also I believe.

The pre cat O2 sensor produces the 171 code.

How long has it been since you replaced both 02 sensors? If it has been awhile, it can make a big difference. Just disconnect the battery for the ECU to reset and "start anew" after doing this.

Second most likely cause is a bad upstream O2 sensor. They will wear out over time and can fail, but the heater circuit still works so you don't get that second code pointing to the O2 sensors.

Don't believe I've done O2 sensors in my ownership (3+ Years), probably something that needs to be done. I replaced from just behind the cat back with a cheap stainless exhaust, but the cat and forward is pretty tired also. The cat heat shield rusted loose and had to be reattached with pipe clamps sort of tired. I wouldn't even be surprised if there was an exhaust leak in there around or before the O2 sensors, or if the O2 sensors hadn't been replaced in 5 years or more.

Any air leaks between the MAF sensor and the throttle body can produce it.

Not to be a downer but most likely you are still going to have the code. The most common cause of P0171 is a vacuum leak, here's a great video on how to check. It's simple and free:

This is my biggest suspicion. I should be able to address this issue with swapping the factory airbox back, but that won't be for another few months at the earliest.

One other thing that might feel like a "misfire" is often the TPS (Throttle Position Sensor). I have had to replace mine 4 times in the 13 years I have owned my rig. RECOMMENDATION: ONLY USE OEM TPS SENSOR - NOT AFTERMARKET!

The check engine light and codes are quite clear that the things that feel like a misfire, are a misfire (also fun when the unburnt fuel causes backfiring).

 

[gamefreakgc]

Looks like you have a game plan. Let us know how the repairs go!