Fuel Trim Bank 1 Driving Me Bonkers

Hello!

I've got a stock 95 2.4L RWD Tacoma with 145,000 miles (she's old but she's still kicking!) who is currently giving me some grief. Back in May she started idling rough, juddering on acceleration and threw a CEL for the Mass Air Flow Sensor. I replaced it with an aftermarket part (A-Premium) which fixed the light and seemed to fix the symptoms. Fast forward to now and the new sensor failed with the same symptoms and a CEL for Fuel Trim Bank 1. Like before I replaced it with a new aftermarket sensor (whichever one O'Reilly's had in stock because I just needed her working) which seemed to barely fix it, but now the engine is running VERY rich, and she will still sometimes idle rough.

Fool that I am, I thought this may have been due to the new MAF being defective and tried swapping it out for a THIRD sensor (Beck/Arnley) which... fixed nothing and threw the code for Fuel Trim Bank 1, again! So now I've got three MAF sensors (one of which I can return), and an unhappy but mostly working truck. It seems like OEM sensors are VERY pricey where I've been looking, and I threw the old one away before I knew how much it would be to replace it so I can't just clean the old one and try it. Knowing what I know now, I'm kicking myself for not holding onto it. And obviously throwing a bunch of generic aftermarket sensors at the problem hasn't fixed it (since all the different brands I've bought look nearly identical). I did add some Seafoam injector cleaner which helped some of the symptoms, but it seems like a bandaid not a solution.

So, my question is - what should I do next? I'd love if the problems could be solved easily with a reliable aftermarket sensor if someone has a recommendation, but with her age and track record I'm guessing it's more than one issue. No other part of her fuel system has ever needed replacing until now, so if there is something else I could try to get this old truck back on her feet I'd be very grateful to hear it. Thanks in advance, and have a great day!

 

Pop a coil out and see if the tip is covered in oil. If it is, you need a new valve cover and spark plug tube gaskets, maybe. How many miles on plugs?

 

Too many! Upwards of 10,000 at least. I've never changed them since I got the truck in 2019, not sure if a shop has. Last servicing where they could have changed them was about 15,000 miles ago.

 

Let’s start there, then. Replace brittle or dry rotted vacuum lines, too.

 

You need a scan tool.
You need to graph the A/F sensors, O2 Sensors, Short Term Fuel trims, Long Term Fuel trims and MAF data.

And the exact code it throws would help us too.

 

Popped two coils with the engine cold and they both looked clean, with no oil pooling either. The hoses all seemed pretty fine as well, some were a bit dry but no cracking on any.

 

I hope you still have the factory MAF... Toyotas dont really work well with aftermarket EFI parts. Having said that, you can fire the parts cannon at this all day long and not fix it. Start with a compression test and verify that the motor is sound mechanically first. When was the last time the valve clearnaces were checked?