Skip the auto shop - Our mechanics make house calls

Q: when my car idles it starts to miss and check light comes on po300 i replaced plugs and ignition coils still does it only at idle

asked by on

my car misses at idle only po300 top speed is good no misses replaced plug and ignition coils still misses at idle

My car has 173 miles.
My car has a manual transmission.

A: Hello. There could be a few different possi...

Hello. There could be a few different possible problems that would need to be checked. The complete intake air system has to be checked for vacuum leaks or cracked intake air tube between the throttle body and airflow sensor. Check the airflow sensor for contamination. Have the engine checked for acceptable cylinder compression of between 142 psi and 185 psi with less than 14 psi difference between cylinders. The O2 sensors should be working normal at idle switching between 5 to 10 times a second. Contact a technician, like one from YourMechanic, to inspect the misfire on your vehicle and replace any failing parts.

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!

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: My car is having all sorts of problems. My check engine light is on. We tuned it up, changed both O2 sensors, checked fuses, and n

Quite often, when one mechanical problem occurs, others are quick to follow. In most cases, they are not related to the same components being faulty. It is possible that during service of replacing or cleaning other parts, a battery cable...

Q: My car is having starting issues - 2002 Hyundai Sonata

Hi there. From the description you have provided, your vehicle's start and stall may be more serious due to the knock you hear. Assuming the engine does not have a mechanical problem (e.g., collapsed or worn piston skirt, connecting rod...

Q: My van used to lock on the central locking key fob and also used to beep at me if i left the keys in the ignition, but it has now stopped.

Hi there. The issue is with the key fob. Either the key fob has lost the communication with the vehicle or the battery in the key fob has failed and needs replaced. If you need further assistance with your vehicle...

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 Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...