my girl has a 98 civic ex and intermittently while cruising at freeway speeds it loses power and the throttle is unresponsive. out of no where it will slam into gear and go back to normal. after happening a few times i scanned the car and no codes. finally the light came on with po171.. related? i have my doubts but i am unsure. checked all the basic stuff- vaccumm leaks, o2 sensors, intake and exhaust leaks, back pressure, ect. did some research and found people had a couple common issues with a lean code (fuel pressure regulator and rear o2) i replaced them since they were cheap.. i swapped her cars for a week and drove over 220 miles with no isses... just had dinner with her and on her way home it f'ed up out of no where. really stumped any help would be greatly appreciated

 

Test your fuel pressure. You can rent/borrow/buy the tool from your local parts store.

 

i already checked fuel pressure with and without bypassing the fuel pressure regulator and it was fine :/

 

Does your battery light come on at all? Sounds like a faulty alternator possibly?

 

its never come on and battery is about a year old