1996 Lexus LS400 - 208k miles

So had something weird happen with my lexus today. If this relates to the story I did have to jump the car before driving.

I jumped my car and went to get emissions testing done, which it passed, then drove to the store. When leaving the store, I pulled out onto the main road, gave it gas, but there was no response at all from the throttle. I was flooring it, but the car wouldn't accelerate beyond 1000-2000 RPM. I turned on my hazard lights, and after about 15 seconds, the car finally responded and started acting normal again. Later that night, I took it for a drive to try to recreate the issue and see what might be going on. While driving, the check engine light came on with the code P0171. I haven’t looked into anything else yet, but I figured I’d ask here to see if anyone else has run into a similar issue or has suggestions on what might be causing this.

Thanks!

 

Interesting. Usually, being stuck at 2000 rpm or less points to limp mode, but your car correcting itself may be the ECU deciding to use default values for fuel trims due to unmetered air

I know that first gens use the "two-trip" diagnosis method, where you have to drive the car twice and the ECU has to see the same problem repeatedly to trigger a check engine light. I believe that would still be the same for second gens

P0171 is a code for excessive air in the exhaust. Time to check your intake for leaks/cracks. I'm assuming other parts are ok in your exhaust system, like the EGR pipe and the exhaust itself doesn't have any holes in it.

Make sure the neck for the intake doesn't have any cracks in the plastic, such as where the vacuum line for the idle up valve connects to it. Anything past the airflow sensor that's letting in air could lead to this issue.

 

Sorry for the super delay to this figured I would share issue was resolved a week or so after this post but turned out my fuel pump was failing and did die

New fuel pump and everything runs find now

 

thanks for updating us. i was going to suggest fuel pump as well since the engine was lacking fuel and thus the CEL!

i'm astonished that you can pass emissions immediately after a jump.
us in CA, the car would need to complete all monitor readiness like EVAP, CAT, etc before i could pass. this usually take 2 heat cycles depending on car! maybe on a 96-97 it doesn't need it? or AZ is less strict? both? oh well, glad you are sorted!