reisjdmd

99 AWD, 135K miles. gas mileage right now, since problem started, is dreadful, at about 12 MPG [used to be a lot better]. out of the blue, on the freeway, it started occasionally bucking [felt like driving over a lot of potholes]. about the same time the P0171 cel appeared. we chased that down with bank 1 sensor 1, and MAF, replacement. but, it still occasionally bucks at 55mph, and the P0171 still comes on a few moments after it starts with the occasional bucking. we thought it might be the torque converter slipping when in 4th gear [OD on]. we tested this by driving for 1/2 hour at 55mph with OD off. absolutely smooth. turned OD on, and it ran normally, but started occasional bucking. while it was bucking, i turned the OD off, and it instantly smoothed out. it shifts smoothly in all gears. only toyota fluid has been used. the fluid is pink and clear. since the problem only occurs with the OD on, at HY speeds, what am i facing??? any advice appreciated. should i just drive with OD off; keep mostly under 60-65MPH and hope for the best [rpm's are about 3,200 at 60 mph; i cruise at 55MPH]?? i don't like that approach, but that would work for the 3+k miles/year i put on it, as it is a weekend driver only [25 miles round trip to town and back, a few times a week]. i'd hate to stick 2-3k into a car worth about 6k.

reisjdmd

anybody out there? i could really use some advice. we are sort of stumped here. suv runs/shifts perfect except at around 55 mph, when light pdeal pressure causes occasional bucking [only with OD on]. if i turn OD off, everything is perfect.

salimshah

Check this out
http://repairpal.com/OBD-II-Code-P0171-and-P0174


Salim

reisjdmd

salim

i have already seeen that, and we tried to eliminate/correct the likely causes. it still occasionally bucks, but only with the OD on, and only arounbd 55 mph. i can drive 70mph with the od on and there is no problem. i can floor it and accelerate and there is no problem. it is only with slight throttle pressure at low rpms in OD that it bucks. does the throttle position sensor come to mind??

salimshah

My focus is still on the error code and you are looking at the drive.

In OD engine power (misfire etc) gets amplified due to gearing. I would try to fix the CEL first before chasing the drive. I am assuming that do get the CEL along with the lurch.

I think you need a realtime obdII reader to record the sensors when the lurch happens.

TPS would be unlikely. RX is cable throttle and the TPS is more for kick down.

Salim

reisjdmd

thank you salim. yes, the code appears very soon after the intermittent first bucking starts. the car is in the shop now. my mechanic agrees with you. he thinks it sounds like ignition misfire. he will track down P0171 possibilities again. maybe we overlooked somthing the first go around. anything but a transmisssion problem, please, please. if i learn anything, i will post it.