Skip the auto shop - Our mechanics make house calls

Q: P0300 codes while idling

asked by on

I have been getting p0300 codes on my van this past week. The codes only appear while idling. I’ve checked and repaired a few vacuum lines, cleaned the mass air flow sensor, cleaned the throttle body, installed new plugs, cap and rotor, ran fuel injector cleaner through the fuel system, checked the for intake manifold leaks and more. So I decided to pull the plug on the mass air flow sensor and all of my misfires were gone. My van ran great with no problems! I bought a new mass air flow sensor and installed it. I cleared the mass air flow code and started it up. Less than a minute later p0300 codes showed up again. So I unplugged the new one and the misfires were gone. Can you tell me what’s going on? Should I return my new MAF sensor? Is this something I should worry about?

Hello. If unplugging the MAF sensor causes the engine to run better then there is a secondary air leak into the engine. This means that there is a vacuum leak from someplace. Most of the time on this engine it is from the intake manifold. It may also be a rich condition that can be from the fuel injection unit.

I usually check this by installing a scan tool to see what the fuel trim readings are. This will tell me if it is getting too much air or fuel and where to start. I have seen more intake manifold gasket failures on this engine than anything else. If you are going to have this repaired, consider YourMechanic, as a certified mechanic can come to you home or office to diagnose your Check Engine Light and repair it accordingly.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. P0300 codes while idling

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

Q: Keep burning out ac clutches

The clutch is burning up due to slip of the clutch overheating the clutch and melting the rubber. The reason it is slipping is the compressor locking up at the higher RPMs. You will need to reclaim the A/C refrigerant...

Q: Clutch slave cylinder

Hi, thanks for writing in. If your slave cylinder is leaking in this vehicle, I would not recommend driving it at all. It is very likely that within just a few applications of the clutch, you could lose all of...

Q: Diagnostic reads 12 and 22. Jeep is idling at just over 1000 rpm (drives itself at 50km/hour.)

Hi there. Yes, the code 12 is for a battery disconnect to the PCM of the vehicle. The code 50 means that there is an error with the PCM. The code 26 means that there is an electrical input issue...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.