Po171

[ColoradoMTNlivin]

99 sr5 v6 195k. Gas mileage has plummeted downhill to about 11-12. Idling at about 1k in park, 700 in drive with foot on the brake. Rough initial acceleration from a dead stop, then runs fine, then stutters/misses/bogs at between 40-50 mph mid gear. I was cruising at about 45 and it suddenly just started slowing down as I was giving it gas, and I had to pull over, shut er down, and then fire it back up. Had a a/f mixture ratio error, and a cylinder #4 misfire. I replaced the fuel filter, cleaned the MAF sensor thoroughly with MAF sensor cleaner, and put a new air filter in just to be safe. Truck started running noticeably more powerful and responsive, but is still stuttering on initial acceleration and between 40-50 mph. Now my cylinder #4 misfire error has cleared, but I'm still getting the p0171 system too lean error. I've done extensive research on here and it seems like it could be multiple things. Given this specific case and symptoms, what do you 4runner gurus think the likely culprit is?

 

[SgtAbn]

I am having similar problems, I think we both need a new Mass Airflow Sensor, its easy enough to switch yourself.

 

[gamefreakgc]

P0171 goes something like this:

50% chance it's the MAF
30% chance it's a vacuum leak
29% chance it's the front O2 sensor going bad
1% chance that you'll be chasing the code the rest of your life.

Check for vacuum leaks first, cheap and easy to do. Cleared my P0171, but it came up after doing some serious engine work so I knew I must have damaged a hose or gasket or something.

If you have someone you can swap parts with, that's ideal since you don't have to spend money. My $50 junkyard MAF (taken off a Camry) is working great.