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1996 F150 I6 300 4.9L- Wants to die out after coming to a stop

05-12-2021, 06:25 PM
Hello everybody hopefully I can get some guidance on what to do here and where to start, thanks.

Truck was running great a few weeks ago until one day it started hard & ran super rough and threw these codes -
P1131 - lack of upstream heated oxygen sensor switch sensor indicates lean bank 1

P1151 - lack of upstream heated oxygen sensor switch sensor indicates lean bank 2

P1507 - Idle air control under speed error

Pulled out the MAF & IAC end cleaned them (with the proper spray making sure not to damage them),it ran a little better and started a bit quicker. CEL still on but wanted to see if it would go away on its own without clearing.
Drove only a few hundred feet & it blew a brake line so had it on jack stands a few days, fixed it and then went for a drive, after the first stop sign it started to sputter and chug up to 10-12 mph, after that spot it seems to have the same power and drive fine. If you try to floor it it will basically die out to almost nothing, you basically have to let off the brake and let it coast and just feather it until it gets past 10mph then its normal. Also doesn't want to rev up in park, drops to like 300 rpms when revved.

Got home and plugged it in the first three codes are still there and three new ones -
P0171- System too lean bank 1
P0385 - Crankshaft position sensor "B" circuit
P0102 - MAF circuit low voltage input

Got under the hood and found an obvious vacuum line leak (basically split in half) and sealed it up real tight, but seemed to make no difference when I rev it up, still seems like it choking or something.

Do you have to let the system run for the sensors to recalibrate or something else for it to relearn? it was definitely not good for the engine but made no difference as I said. Reading the codes it seems like the MAF, IAC & Crankshaft sensor could be failing due to not getting enough power causing the lean codes, does it sound like a computer issue? I can't imagine all 3 going bad at the same time basically but this type of diagnosing is not my forte so not sure. Once I know what it is I'm capable of fixing it but the diagnosis is a different story. Also not inspected ATM so doing a drive cycle is hard and don't want to clear it until I have a better idea of what's going on.
Any help at all is greatly appreciated!

05-13-2021, 10:01 AM
Kinda sounds like an exhaust restriction. Plugged cat maybe? Usually test bungs in front of the cat that you can remove and see if it will rev up.

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