Skip the auto shop - Our mechanics make house calls

Q: Rough idle and engine misfire

asked by on

Ford focus mk2.Car have a rough idle and misfire,smell like raw fuel, causing limpmode when driving(malfunction transmission).Car have no power when accelerate. Took car for diagnogstic with no success.Service transmission,still have the same problem.

My car has 189000 miles.
My car has an automatic transmission.

A: Engine misfires can be caused by many diffe...

Engine misfires can be caused by many different problems, but there are a few suspects that occur more than others. Generally, misfires are caused by either a spark or fuel issue or in cases, a combination of both. Spark related problems generally will result from things like ignition coils, crankshaft position sensor, spark plugs, spark plug wires or ignition modules not working properly.

When the misfire results from a fuel related issue, this is commonly related to a lean fuel condition (lack of sufficient fuel supply to the motor). Fuel related misfires can be caused by many different things such as low fuel pressure, faulty or dirty fuel injectors, a faulty O2 sensor, a dirty or failing mass air flow sensor, a faulty or dirty idle air control valve or a vacuum or intake leak. When the fuel supplied to the combustion chamber is insufficient, this results in an ignition (spark) that is igniting a less than balanced load of fuel and air. This results in a misfire or an explosion in the cylinder that is much less powerful than the other cylinders. This creates a loss of power that resonates throughout the motor additionally causing other problems with ignition and fuel timing. Due to the number of different things that may cause an engine misfire, the quickest and easiest way to diagnose this type of problem is to hook the vehicle up to a scanning tool which will download any potential fault codes that may have registered in the vehicle's computer as a result of the poor running condition. I would recommend having an expert from YourMechanic come to your location to diagnose your misfiring problem.

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・Save up to 30%

Get a quote

What others are asking

Q: Cylinders 4 and 5 are misfiring - 2007 Mercedes-Benz S55 AMG

Hello. Most of the time if there is a misfire on those two cylinders it is not caused by the computer. Typically it is caused by either failing spark plugs or an internal problem. I usually start by doing a...

Q: My car is overheating and leaking from somewhere - 2005 Nissan Altima

Hello. You may have a leaking water pump or cooling fans that are not working. I recommend having the cooling system performance tested and pressure tested by a qualified mechanic. Since it is overheating already, you may have blown a...

Q: Windshield wipers leaving spot on driver's side

This is not really my area of expertise. Looking online, I have seen some people suggest using steel wool but I would be very careful with this approach. Test the steel wool in a small, inconspicuous place before using it...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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.