Car slightly jerks, stalls, and then restarts

ANSWER : You should have the check engine light and engine scanned to see if the engine may be running lean due to low fuel pressures or clogged injectors. You should also have the mass airflow sensor cleaned and checked for proper readings and replace if not within specifications. The vehicle runs richer in colder weather and may be the reason for not stalling. You should clean injectors, clean throttle body and idle control valve then clean mass air sensor and relearn idle.

ANSWER : Trouble Code P0335 is a crankshaft position error code if I remember correctly and it sounds like you replaced the camshaft position sensor inside the distributor. If the scanner you have shows live data, you can watch the engine rpm numbers while the engine is running and if they do not match the tachometer on the dashboard or you can see the reading cut out right before the engine stalls, you may need to replace a faulty crankshaft position sensor. To avoid any unnecessary repairs, consider hiring an experienced technician like one from YourMechanic to come take a look at what’s going on and offer a personal diagnosis of the stalling issue.

ANSWER : Hello. A faulty coil pack is likely the cause of the issue you are having. A less likely cause could be a clogged fuel filter or fouled spark plugs. I suggest that you have a technician inspect your coil pack to be sure it has voltage and ohm readings according to manufacturer’s specifications, also be sure it has a good electrical contact.

The technician should test the fuel pressure of the system as well. Make sure the fuel pressure reaches the manufacturer’s specifications. Also inspect the spark plugs for oil fouling and bad electrodes.

If you’d like to get this fixed, consider YourMechanic, as a certified technician can perform these checks and properly diagnose your stalling issue.

ANSWER : Hi there. What had happened is the wrong key set the security to the vehicle. This is to prevent the vehicle from starting with the wrong keys. Try removing the battery cables (+) and (-) for 13 minutes. During that time, put the original key in the ignition and turn it on. Activate everything in the car even though there is no power. Then remove the key and hook up the battery cables. The computer should have reset and reset the security. If the security is still being tripped, then I recommend seeking out a professional, such as one from Your Mechanic, to help you

ANSWER : There are reports that the replacement alternators will not communicate with the engine computer and will not charge correctly. I recommend using only the manufacturer approved replacement part. It can be new or remanufactured but approved for use in the vehicle. Some lower cost alternators on the aftermarket will have charging problems since they will not communicate with the ECM on the vehicle and will stop charging.

ANSWER : Hi there. Usually when you shift into reverse and engage the brake it will cause the engine RPM to drop; as it’s creating a load against the transmission and the engine. If the engine stalls, it may be caused by a faulty idle control valve, bad O2 sensors, or clogged fuel injectors.

In regards to the "pan", we’re not sure what you are referring, so it may be a good idea to contact one of our local professional mechanics to complete a battery inspection to determine what’s going on with your 2010 Ford Focus.

ANSWER : Hi There,
The air box resonator missing should not impact the running condition of your vehicle at all. If the air box had cracks in it, this may have caused excess air to be injected into the intake system which may affect the reading of something called the mass air flow sensor which meters the air intake into the engine. When this is producing faulty readings or detects abnormal air intake, this may cause the jerking reactions you describe. The mass air flow sensor monitors air intake as it is mixed with fuel prior to being injected into the motor. This sensor relays vital information to the ECM which uses this to make adjustments to fuel supply to the motor. A dirty or faulty sensor can cause an imbalanced air/fuel load to be supplied to the motor which results in an over fueling or under fueling situation depending on the conditions. This type of inconsistent fuel supply to the motor may cause a hesitation, loss of power, a jerking reaction, potentially a bit of black exhaust smoke and typically a strong smell of fuel when this sensor is malfunctioning. I would suggest having a professional from Your Mechanic come to your home to diagnose and inspect your vehicle.

ANSWER : Have the computer checked for codes to see if the EGR system is malfunctioning. The ECM is not a common failure, and the failure may be caused by the EGR system or the engine having a misfire in one or more of the cylinders. The wire harness on these vehicles has very small pins and sockets and are very susceptible to connection issues at any of the engine sensors. This can cause multiple codes to be stored in the computer. The list of possible connections that could have a problem is very long and includes the ECM and all the engine sensors. The first place to look is at the connections to the crankshaft and camshaft sensors. If you would like to have this diagnosed, a certified technician from YourMechanic can come to your home or office to inspect your stalling issue and recommend the appropriate repair.