I randomly got a check engine light while driving and I got the following codes:

P0100
Mass Air Flow Circuit.

P0110
Intake Air Temperature Circuit.

P0141 (repeated once)
Heated Oxygen Sensor Circuit – Bank 1 Sensor 2.

P1135 (repeated once)
Air-Fuel Sensor Heater Circuit Response.

P000110
????
(This could be an error since I'm using a cheap scanner with third-party software on my phone)

The only symptom I'm getting is an intermittently rough idle like as I would expect from these errors. No noticeable loss of power, no hesitation, no stalling. From what I've read, all of this is localized in the MAF sensor, which could mean that it took a dump.

The only recent work I've done was deleting the intake silencer and replacing valve cover gaskets 2 weeks ago. I checked plug tightness on my MAF sensor and all other sensors I disconnected during that work and everything is fine. I've looked up the combination of these errors online but I only found one thread that didn't have an answer. The only thing I haven't done yet (just got home) is running it with the MAF sensor unplugged to see how it runs or idles.

Definitely need some help on this one. I'm planning on getting rid of my other car and this beater needs to be reliable.

I'll give you a hint and tell you how it runs with the MAF unplugged - very quietly because the engine will cut off the fuel and stall almost immediately.

Check your MAF wiring and ensure it's all intact and smooth. Same goes with the Oxygen sensor, make sure it's sound and plugged in. You are getting MAF codes and O2 sensor codes as though it's not even plugged in. Could also be a pinch or damage in the engine harness itself.

A new DENSO MAF sensor will run you around $70, and a new DENSO O2 sensor about $60. Double check your part numbers here:Find My Part. Best to see if it's a wiring or connecter issue first though before you are out $130. Someone will eventually chime in and say "clean your MAF its dirty" but dirty MAF's rarely throw a code, they just get bad gas mileage. Yours is throwing circuit codes, not rich/lean codes so something in the circuit to the ECU is broken.

Well all of these codes popped up at the same time. My O2 sensors are new-ish. I'm not sure how close one of the O2 sensor wires might run to MAF sensor wires in the engine bay outside the main bundle of the harness, but I didn't see anything wrong with the MAF sensor harness. Not too close to anything hot, nothing frayed. I feel like the completely unrelated codes are from a common issue.

I can read a wiring diagram but I can't seem to find one and I no longer have access to Chilton's Database.

Check the ground near the diagnostic plug on the engine, driver's side--aka the sensor ground. I'm not saying that's it, but it's the first thing I'd do.

I don't know if you have to dig that deep by going to a wiring diagram but it sure can't hurt. From my knowledge of the MAF wiring I don't think there's a common circuit with the two except for a ground like TheDurk mentioned. The other wires in the MAF is the IAT temp circuit, 12V power, MAF signal wire, and fuel pump circuit. I don't think the O2 has any of those in common.

If you are not seeing any visible damage to the engine wire harness, then assume the components themselves have failed. Still very weird to have two fail at the same time. I checked the FSM for those codes and the common denominator is the ECU. ECU failures are rare but it can happen.

I would order the DENSO parts needed from a place with a very generous return policy (Amazon maybe?), that way if you replace say the MAF and it still throws a code, you can return it.

Trouble codes cleared themselves after 300 miles...

Trouble codes are back. This time BOTH O2 sensors came up, also getting a lean code. Truck is driving differently now... Noticeable loss of power and fuel economy, it has stalled twice at low speed. My assumption is that the MAF sensor has failed and is causing everything else down the line to do their thing.

Ordered a used MAF sensor on Amazon for $30 and it should arrive tonight.

Installed the new MAF sensor. Engine is running much more smoothly. No stalls or loss of power. Cleared codes. O2 Sensor codes never came back. MAF Sensor codes never came back.

Check engine light came back on. Getting the following codes:

P1130
Air/Fuel Ratio Sensor Circuit Range/Performance Malfunction Bank 1 Sensor 1

P0171
System Too Lean Bank 1

P300000
????

Bump.

Could use some further assistance. I am basically stuck.

Checked all the vacuum hoses? What brand sensors did you buy? Non-OEM
can fail quick.

I purchased what I thought was a used OEM part. Turns out it was generic Chinese. I have since then replaced it with a brand new OEM sensor and have driven it around for about 100 miles. Codes have not cleared and now it is starting to stall again at sustained low rpm, such as cruising at low speeds or idling.

Looked around for vacuum leaks, couldn't find anything. I have recently replaced the intake silencer with a straight pipe but I re-routed vacuum lines the way the guide suggested and replaced some damaged ones while I was at it. After this I drove about 400 miles before my CEL came on the first time when it began to throw MAF sensor codes. I will check codes tonight now that I've put a few miles on it with the new MAF sensor.

Brought it to a mechanic to get a final verdict. He said to replace O2 sensors. I've only had time to do the air/fuel sensor (upstream) before going on a camping trip. Anyway, still getting CEL for downstream O2, lean running, and coolant low temperature (wtf). ~10 miles into my trip I stalled out, engine did not recover from mashing the throttle like it usually does. I pulled over, checked and cleared codes, and did the remaining ~450 miles of demanding mountain highway driving with no incident but CEL still on.

I'm still confused why it can still run like crap because I was under the impression that the downstream O2 sensor only monitors emissions and has no control over the operation of the engine.

I learned a month ago while tracking my fuel trims that the rear O2 does have a slight control over long-term fuel trims, I was very surprised. Mine was fouled out so wasn't working properly and adding too much fuel. However the vast majority of the fuel trims are set by the upstream sensor.

None of the sensors beyond the MAF should cause the engine to stall though, something is very wrong. The low coolant temperature code tells me there's an issue with the wiring or ECU... I don't think you a chasing a sensor problem but rather the ECU is not getting the right voltage signals that it should be.

The A/F ratio sensor new is about $150, rear O2 $50, so this is going to get a little pricey. I mean, you can replace both but it's not going to clear all the codes.

Are you still getting the P0171 lean code though? That's a vacuum leak 90% of the time.

Still working on it, haven't done anything with the downstream O2 sensor yet.

I just remembered that one of my valve covers is cracked into 2 pieces and is being held together with JB Weld. I've been running it like that for the past 3.5k miles and will continue to do so until I replace it when I do my oil at 5k. The JB Weld is probably starting to fail at this point and leaking air.

Don't judge me, I'm aware that this vehicle will not survive my ownership of it.

I just had the P0100 and P0110 codes pop up on me after a valve adjustment. It makes sense because I had to remove a lot of vacuum tubes and unplug stuff. I noticed a higher than usual idle but it could be my throttle cable acting up again.

I don't see how a poor seal on the valve cover could cause those codes. I tried cleaning my maf airflow and I will clear the codes and see if it comes back.

Could a loose engine ground wire cause a problem on the intake system?

Also I have a 3rz-fe engine. I thought non-CA 4runners had only a maf sensor, and no O2 sensors. Is that correct?

Update: After cleaning the sensor and clearing the codes neither returned when I started the vehicle for a few seconds. Hopefully they don't return later. Idle is still high at 1300, but I'm not concerned because that is at startup, it usually drops some.