2004 Random Misfire

Hello fellow Tacoma owners.

I’m hoping you guys have some ideas on what my issue is. I have a 2004 2.4L with the 5 speed. I’ve had it for about a year now. Recently after being parked at the airport for about a month, it developed a misfire. When I first drove it, I kind of wrote it off as I just forgot how slow it was. But the misfire got worse. You can definitely feel it’s low on power especially lower in the rpm range. Recently it’s gotten so bad it’s struggling to idle. Here are the codes:

P0135 - Oxygen Sensor Bank 1 Sensor 1 Heater Malfunction
P0171 - Bank 1 System Too Lean
P0300 - Random/Multiple Misfire Detected
P0301 - Cylinder 1 Misfire Detected
P0302 - Cylinder 2 Misfire Detected
P0303 - Cylinder 3 Misfire Detected
P0304 - Cylinder 4 Misfire Detected

I checked the A/F sensor circuit. The heater element within the sensor itself is ~2.5 Ohms halfway to temperature (within spec). The EFI main relay works as it should. Pins 1 & 2 show the coil resistance and pins 3 & 5 go from open to close when you energize the relay. There is only ~10V across +B and HT on the A/F sensor heater pins when you turn on the ignition. So it could be one of the grounds has too much resistance but I think that is more likely caused by the resistance in the ECM to ground. Also if it was a ground issue why would that occur just from sitting? I think it is more likely a vacuum leak/MAF issue or a fuel issue. If anyone has any ideas with this combination of codes or steps to troubleshooting please let me know. Thanks

 

By chance water is in the gas?

 

And i'd say the sensor heater is separate from the misfire.

i'd start by checking for vacuum leaks around the intake and such. Can you read scan tool live data and/ read the freeze frame for the codes

 

Welcome to TW…Intake air boot cracked?

 

I would start with disconneting all grounding points, clean and proceed from there. There is a post in this formun title All Ground point locations. There is a picture, it shows them easier than it is to explain. It is the 10v for the AF heater that bothers me, IIRC that ground goes through the PCM. The next step for me would to be disconnect the battery and take the PCM out and take the cover off and look for bad capcitors and burned areas. There are a few posts where this is what people have done after they have spent lots of time and lots of dollars throwing parts at it.

 

Thank you all for the replies.

CD20H - There could be water in the gas however I think it is unlikely. It was parked inside a parking garage. It is probably a good idea to drain the tank and fill it with fresh gas, this eliminates bad fuel as a cause too. I do have a separate “issue” (design feature) where the bed will fill up with water after rain. I’m guess most people just drill holes in the bed.

joba27n - I think it is. I can’t say for sure but I think that code was there before the misfire/other codes. Yeah good idea, I will look for vacuum leaks. My friend has a smoke machine so I'm planning to try that as well. I will pull the freeze frame data. I checked the live data while it was running and the MAF values did changed with vehicle rpm and the A/F sensor did as it warmed up (which doesn’t necessarily mean that they work properly)

HondaGM - Thanks! And yeah I’ll have to check that; that very well could be the issue. I didn’t see anything obvious.

Glamisman - I’ll check out that post about grounding, thanks! And yes the AF heater ground is through the PCM according to the electrical diagram for that circuit. Yeah I kind of just assumed removing and inspecting the PCM would be a pain but it actually looks very easy, like 15 minutes.