brandyn85

ok guys i had this problem about a year ago with my 99 4runner did some research on here and eventually replaced my A/F sensor, and i was able to get a used MAF and it fixed the problem.

well my light came on again a couple weeks ago. a friend was following me and said my truck was just blowin black smoke like a diesel. i went in a had it scanned and it was p0171 and p0125. i got on here and did some searching and found that the p0125 may be linked to the p0171, after more testing on the truck i got irritated and went and got a denso a/f sensor and threw it in. i cleared the light and it stayed off for about 30 miles. popped back on so i went and had it scanned again. just the p0125 now. so i did some more screwin around and didnt find any broken wires or anything so about 2 days later i went and got a coolant temp sensor. reset the light again. it stayed off for about 2 days, then i went to get gas and when i started the truck the light came on again! went and had it scanned again and it was just the p0171 now. so what i've come up with now. if i reset the cel the light will stay off, no matter how far i go. but when i shut the truck off and turn it back on the light pops back on and i get crappy gas mileage again. its like when the cel is on my gas mileage is about half what it usually is. i cant figure out what would make it do what its doing. its just weird to me that as long as i dont turn the truck off its fine.

has anyone had an issue like mine? i've tried searching and have come up with nothing. last time i had the p0171 it didnt matter if the truck was warm or cold or if i was driving or not the light would just pop on. but this time im stumped...

kball

The CEL comes on after so many on off cycles. So it's normal to not come on the first time you drive it after clearing it. You say your MAF was a used unit? Maybe it needs cleaning now?

brandyn85

i cleaned it a few days ago, and i cleaned it again today to make sure... i noticed though... after i reset my ecu my mpg goes back to normal, my girlfriend drove it 2 weeks ago up to our cabin, about 135 miles one way. and used almost a whole tank of gas, i reset the ecu and drove it to the cabin 2 days ago and i only used about a quarter tank of gas... im wondering if i need to buy a new MAF, i dont want to replace it though unless i am sure. is there a way i can test it?

kball

Yep, you can test it. Here you go.

http://www.ncttora.com/fsm/1996/SIL/.../mafm/insp.pdf

brandyn85

thanks i havent gotten to it yet, im going to try tomorrow.

brandyn85

hey guys im back! still not fixed. i have since replaced the MAF with a new one, replaced the A/F sensor with new one, both OEM, checked for hours for vacuum leaks with carb cleaner and starter fluid... any ideas? i think im going to go tomorrow and pay the 90 bucks to have a diagnosis done... i dont know what else to check for.

DewDog

It could be fuel pressure too or engine temp sensor. I had the same problem but I found that there was a crack in my intake tube between the MAF and throttle body. Hope this helps a bit too.