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2002 Camry Check Engine Code P1121: Mass Air Sensor or Throttle Position Sensor Issue?

Model: 2002 Camry Fault Code: P1121 Posted: 2007-09-27 15:16

While driving today, my 2002 Toyota Camry suddenly lost power and the check engine light illuminated. The vehicle restarted but exhibited significant performance issues—slow acceleration, a noticeable delay when pressing the accelerator pedal, and an inability to exceed 4500 RPM. A code reader at Advanced Auto showed 'P1121 - Manufacturer Control Fuel Air Metering'. The technician suggested a Mass Air Flow (MAF) sensor issue, though online forums indicate this could also point to a Throttle Position Sensor (TPS). I'm trying to diagnose the problem myself to keep costs low. However, I'm unsure whether this is something that can be safely handled by a DIYer or if it requires professional diagnosis and repair. Can anyone confirm which component is more likely based on symptoms? Is there a way to test these sensors before replacing them?

Related fault codes

P1121

Comments (7)

Anonymous 2007-09-28 08:38

If the MAF sensor is disconnected, does the engine still run at all?

Anonymous 2007-09-29 05:58

The car appears to be running in a limp mode—able to move but with very limited power. It cranks and accelerates slowly, especially when the pedal is pressed. There's a noticeable delay between pressing the gas and response, and it consistently maxes out at around 4500 RPM. Some Toyota technical resources suggest this behavior may occur when the Throttle Position Sensor (TPS) fails.

Anonymous 2007-09-29 08:26

So, based on that, is it safe to assume a TPS fault?

Anonymous 2007-09-30 10:00

Apologies for misreading your original post. I haven’t tested the car with the MAF unplugged—so far, no engine start or run observed under those conditions. I assume the Mass Air Sensor (MAF) and Mass Air Flow sensor are interchangeable in this model? I’ll try disconnecting it today and update my findings. Also, I recently cleaned the throttle body—it was clogged with tar—but that didn’t resolve the issue. It seems a clean TB wasn't enough. Thanks for the input—I'll report back after testing.

Anonymous 2007-10-01 05:55

I disconnected the MAF sensor and attempted to start the engine. The first attempt failed; on the second try, it started and ran without any noticeable performance changes. After shutting off the engine and reconnecting the MAF, it started immediately on the first try with no difference in behavior.

Anonymous 2007-10-01 07:22

Given that, I think it's time to consult a professional—unless cleaning the MAF sensor resolves the issue entirely.

Anonymous 2007-10-05 05:47

I replaced the Throttle Position Sensor (TPS), but the problem persisted. Since new parts cannot be returned if used, I'm now looking for a used TPS at a junkyard. Does anyone have experience testing a TPS before purchasing? The part number is 89281-33010, with Toyota P/N 78010-33010 (as listed in dealer paperwork). If I find one at a yard, how can I verify it's functional and not faulty?