Q: P0300 codes while idling

asked by on July 25, 2016

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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


Experienced Mechanic?

Earn up to $70/hr

What others are asking

How do I enable the power running boards?
The Running Boards on your truck are there to make it easier to get in and out of the vehicle. The Power Running Boards will move to your selected position automatically. To enable the Power Running Boards. Go to the...
Oil light on
Hello. This could be an indication that your oil pump needs to be replaced. However, it could also indicate that your engine is going bad and needs to be replaced. I would recommend that you have a certified technician, like...
Check engine light on & oil pressure dropped
Hello. It is possible that you are getting a false reading as a result of a faulty oil pressure switch. It is also possible that there is an oil leak and that’s what is causing the oil pressure to drop....
Scraped a small layer off of my tire wall; should I be worried?
I would talk to the insurance company if you have full coverage with a low deductible so you can get the rim and tire replaced. If you decide to not go with the insurance route then you should at least...
I need the measurements for brake/shoe pads left and right front and rear wheels
Hi there, thanks for writing in. I have always recommended brakes to be replaced if the pads are worn down (https://www.yourmechanic.com/article/how-to-recognize-brake-pad-wear-patterns-by-cheryl-knight) to 4/32 of an inch and the rear brake shoes worn down at its thinnest point to be 3/32....
Security light on, new key fob cannot be programed
Hello. Your key fob needs to be programmed to your car for it to work. There are a couple of ways this can be done. You could take the key fobs back to the dealership and have them program them...
Brakes are failing no fluid leaks at all and brake fluid resevoir still full
An internal seal failure in the master cylinder is possible and that is easily tested for by either blocking off the master cylinder ports and/or using pressure gauges to measure pressure developed within the system upon pedal application. It is...
Car shaking when it goes above 45-60mph and stays in that condition with check engine light flashes
Hello, and thank you for writing in. The vehicle may be having one of many issues. Shaking is usually caused by some kind of imbalance with the engine and its combustion cycles. This may be a problem with the fuel...
Hello! I have a 2007 toyota camry Se,And I don't know where the "Fuel pressure regulator ",Was located.
Your fuel pressure regulator is mounted to the fuel pump module as part of the fuel pump assembly inside the fuel tank.

Related articles

2012 Chevrolet Traverse vs. 2012 Toyota Highlander: Which One Should I Buy?
Large SUVs are a huge and broad market, with a range of different offerings from economy to luxurious. The majority of the SUVs and crossover SUVs offer decent gas mileage, plenty of room for friends and family to ride along...
The Best Used Cars to Buy If You're a Dog Trainer
If If you are a dog trainer, you expect a lot from your vehicle. You want a ride that is safe, roomy, and of course, dog friendly, since your training operation will often mean that you need to transport the...
Symptoms of a Bad or Failing Top Dead Center (TDC) Sensor
Common signs include the Check Engine Light coming on, car not starting, and engine misfiring or running rough.