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Mazda P0300 Code: Causes, Symptoms, and Fixes for Misfire in 99 Mazda Millenia 2.5L

Model: mazda Fault Code: P0300 Posted: 2008-11-05 15:58

Can a faulty TPS (Throttle Position Sensor) cause a P0300 misfire code? My car exhibits hesitation when accelerating or decelerating, especially during transitions between gears. The check engine light flashes intermittently and recently triggered multiple codes: P0300 (random/multiple cylinder misfire), P0120 (throttle position sensor circuit malfunction), P0130 (oxygen sensor upstream bank 1 sensor 1 fault), and P1170 (coolant temperature sensor circuit). The issue started after I replaced the TPS. My vehicle is a 1999 Mazda Millenia with a 2.5L engine, currently at 152,000 miles. It generally runs well but experiences noticeable hesitation and erratic check engine light behavior. I recently performed a full tune-up (spark plugs, wires, cap, and rotor), yet the symptoms persist. Could the TPS replacement have triggered or exacerbated the misfire? What are the most likely root causes for P0300 in this model?

Related fault codes
P0300
Comments (5)
Anonymous 2008-11-05 18:31

A faulty TPS typically results in a specific TPS-related diagnostic code, not a random misfire like P0300. While a TPS issue can cause hesitation or stalling, it is unlikely to directly cause a misfire. The flashing check engine light indicates the Powertrain Control Module (PCM) is detecting a misfire. Please note: when does this blinking occur? At idle, under load, or at specific RPM ranges?

Anonymous 2008-11-05 18:48

My sister's 1999 Mazda 626 was highly sensitive to worn spark plugs. Given the age and mileage of your vehicle, a simple tune-up—especially with old or degraded ignition components—could be a key factor in resolving misfire symptoms.

Anonymous 2008-11-06 05:23

It's a 1999 Mazda Millenia with a 2.5L engine, at 152,000 miles. It runs fine most of the time, but recently developed hesitation and erratic check engine light behavior. After a tune-up (plugs, wires, cap, rotor) two weeks ago, the symptoms worsened. Last night, codes P0300, P0120, P0130, and P1170 appeared—specifically when I replaced the TPS. Thanks for the insight.

Anonymous 2008-11-06 08:52

Did you install high-quality spark plugs along with reliable ignition wires, cap, and rotor? You now have a P0120 code indicating a TPS circuit issue—before blaming the sensor, verify voltage, ground connections, and wiring integrity. Also inspect the upstream O2 sensor for faults. Do not assume the TPS is faulty without proper diagnostics.

Anonymous 2008-11-06 09:46

Inspect the rubber air duct between the throttle body and airflow meter. If it's cracked or has holes, it can cause inconsistent airflow readings, leading to misfires. Try temporarily taping over a split section to see if performance improves—this may confirm the issue and indicate the need for replacement.