Q: PO300 and PO420 and rough idle and RPM fluctuation

asked by on

For the sake of diagnosing, I have installed new spark plugs, spark plug wires and boots, new engine coil packs, EGR valve, EGR modulator, new tubes in the EVAP system, vacuum switch valve, vacuum control valve, Purge solenoid and a new Idle Air Control valve.

My car is having a rough idle every once in a while (and seemingly getting worse) and would hesitate accelerating because of whatever issue is going on. There are no audible sounds but it feels like the car is kicking while trying to accelerate and there is a hesitation to the acceleration. It also has a rough idle just sitting in drive or reverse with the brake on. This only happens in drive and reverse.

It would help with diagnosis if you included the vehicle year, make and model with engine size. Since the engine is running good out of gear and only gets rough when in gear you either have a bad motor or a transmission mount that is not supporting the engine and allows excessive movement when accelerating.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. PO300 and PO420 and rough idle and RPM fluctuation

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.