Car hesitant to accelerate after a complete stop.

ANSWER : Hi, thanks for writing in. Sorry to hear of your difficulty with your 2012 Sonic. The good news is your Check Engine Light is on, so what means the fault has been "recorded" by the engine computer and diagnostic codes will be available to the mechanic to search for the fault. The codes don’t necessarily indicate which "parts" have failed but rather will indicate which systems are malfunctioning and causing poor operation of the engine. Individual components in these systems will then have to be tested by the mechanic. The traction codes may or may not be related to the issue with the engine, the poor acceleration, but those traction codes will have to be evaluated as well. It is possible there is more than one problem. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect your vehicle for you and download codes your car computer has stored, and make or suggest any repairs as needed.

ANSWER : Hello. There are several problems which could affect poor idle and low speed running. Starting with the misfire indicated by Check Engine codes, bad spark plug coils, especially with your mileage. Check also for oil leaking from the valve cover into the spark plug recesses – this will cause shorts and misfiring as well. A dirty or sticking idle air control valve and/or throttle body, clogged fuel filter can cause poor low speed running as well. I recommend having a certified technician diagnose the misfire in person for a precise diagnosis and repair.

ANSWER : This kind of reaction is often a sign of low transmission fluid or a faulty transmission control solenoid. As you know, automatic transmissions use pressurized hydraulic fluid to change gears. Every time a gear change is required, the car’s computer activates a transmission solenoid, which directs transmission fluid into the valve body to engage the correct gear. When this is faulty or not working properly, this can cause a delay in gear shifting or in some cases cause the car to not shift at all. This type of problem is amplified any time the transmission is low on fluid creating a drop in hydraulic pressure. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

ANSWER : As you may know, your car’s AC system when working properly puts an extra load on the engine at all times when it is running. When this happens, your car’s computer makes adjustments to compensate for this extra load on the engine. There is a component in your engine’s intake system called an idle air control valve that helps to control air intake as it is mixed with fuel during idle or low speeds. When this is dirty or not working properly (especially under load from additional power required for the AC), tis may cause incorrect adjustments to be made to the fuel mixture causing the hesitation you describe. I would recommend having an expert from YourMechanic come to your home to take a look at your car to properly diagnose and repair your idle air control valve.

ANSWER : Hi There,
The hesitation accelerating after the light comes on is likely due to the ABS and traction control system intermittently engaging. Your car is equipped with wheel speed sensors at each of the four wheels which monitor wheel speed while relaying this information simultaneously to the ABS and traction control system which are controlled by the car’s ECU. When the ECU senses an abnormal speed given specific conditions, it engages the ABS or traction control as needed to control the vehicle properly and safely. Occasionally, these sensors can fail or become faulty working intermittently sending inaccurate signals to the ECU. When this happens, you may experience the symptoms you have described. The ABS or traction control system may be inadvertently activated by these false or inaccurate signals. I would suggest having a professional from Your Mechanic come to your location to diagnose and inspect your vehicle.

ANSWER : Hello, thank you for writing in. The vehicle may be suffering from several different issues. In this type of situation you want to start with the least complicated option, and work your way up. Start by making sure your tires are properly inflated, and have them balanced. Your brakes may be playing a role, and you will want to start by cleaning them off with some brake cleaner, and make sure nothing is stuck between the pad and the rotor. You can then raise the vehicle and manipulate the wheel looking for excess play, damaged axles and joints, and damaged wheel bearings. From there you may need to look into the wheel assembly itself and make sure there is nothing mechanically wrong, dirty, or damaged. For more help diagnosing or resolving the vibration issue, contact our service department to schedule an appointment.

ANSWER : Unmetered air can cause this type of hesitation and shuddering. Too much air compared to fuel will cause a lean misfiring condition. Fault codes need to be read out of your Mercedes C320’s engine computer to see if there are any underlying issues and those issues are corrected.

The induction should be inspected and checked for vacuum leaks. Also, fuel pressure and volume should be checked as well if the induction system checks out okay. A partially clogged fuel filter can cause a starvation issue on heavy acceleration. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will have the tools and expertise to conduct this type of diagnosis and repair for your acceleration issue.

ANSWER : It sounds like you may have a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. This valve is controlled by the vehicle’s computer and will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. This is also an important function when starting the motor as it allows the motor to run and idle on it’s own once the motor fires. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve making the transition from a higher RPM back down to idle speed while adjusting the air/fuel ratio constantly to allow this to happen smoothly. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.