My 2001 Toyota Camry CE (4-cylinder gasoline engine) has run rough and shaky the last several weeks and several hundred miles. The car has about 226,000 miles. I bought the car new and have generally done regular maintenance. In general, the car has served me well for these 17 years and given me few problems.
Check engine light appeared and resolved
In June 2018, the car was running fine, but the Check Engine light appeared. I used my OBDII scanner and got code P1135, which apparently is a bad upstream air fuel ratio sensor. That's a very easy repair on this car, so I replaced the sensor with a new one and cleared the code. The Check Engine light went off and stayed off, and for a week or two, the engine continued running fine. Please note that the only symptom of problems at this point was the Check Engine light itself.
Evidence of engine trouble
A week or two after the air fuel ratio sensor replacement, I started hearing and feeling occasionally that the engine was not running 100% smoothly. It was as if the engine would suddenly slow down and then speed back up once in a while. The problem has become more consistent in the ensuing weeks. At this point (August 2018), most accelerations produce this rough, shaky behavior and sound, where the engine goes fast then slow, fast then slow, fast then slow, probably three times per second. This happens both while accelerating to highway speeds and while accelerating to 25 MPH on residential streets, most of the time but not every time.
I made this video to illustrate the problem. The audio quality isn't great. You can hear the problem best at 4:22 when I'm accelerating to 25 MPH; you can also see the video shaking up and down slightly as the engine goes fast then slow, fast then slow, fast then slow.
What I have tried
- Oil (full synthetic) and filter are recent (four months ago, 2,800 miles ago)
- Fluids are topped off (oil, coolant, power steering, brake)
- For what it's worth, the car passed its biennial emissions inspection four months ago
- Replaced upstream air fuel ratio sensor (as mentioned above) (one month ago, 600 miles ago)
- Replaced air filter (it was due) (two weeks ago, 300 miles ago)
- Applied Gumout Regane Complete Fuel System Cleaner (10 days ago, 200 miles ago; it's about half gone by now)
- Replaced spark plugs with platinum spark plugs that claim to fit my vehicle (today, just before taking the video)
None of these actions seem to have made any difference.
Update: code P0171
A day or two after replacing the spark plugs, the Check Engine light returned but with a different OBD-II error code: P0171, System Too Lean. The interwebz say this could indicate a variety of problems, including a mass air flow (MAF) sensor problem.
What should I try next? I am a DIY kind of guy who works with computers for a living, so I won't attempt any major auto repairs. If my best move is to go to a mechanic, please say so. But if there are other simple and relatively inexpensive things I should try, I would love to hear them.