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Q: Engine hesitates for 2-3 seconds before moving when accelerating from a stopped position.

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No SES light in dashboard so there's no code to recover. Problem occurs every time car is at a stop, but once the car starts moving the engine is fine. Engine starts and idles smoothly, idling RPM is 600. No unusual sounds or odors present. In the past six months I've replaced all six fuel injectors, all six ignition coils, knock sensor, all six spark plugs, air filter, and the starter. All new parts installed are OEM. What's the likely culprit that's causing this problem??

My car has 114000 miles.
My car has an automatic transmission.

A: The first thing that came to my mind was th...

The first thing that came to my mind was the Mass Airflow sensor, or MAF. This sensor is located in between the air filter box and the intake manifold. It is the primary sensor input for the amount of fuel delivered. It can become dirty, or it can provide a "biased" reading.

Because it is still providing a reading (even though it may be wrong) it will not set a trouble code. It will take a few seconds for the computer to deduce from the throttle position sensor, TPS, and the Manifold absolute pressure sensor, MAP, that you are attempting to accelerate and add fuel.

The diagnosis is an easy one. Simply unplug the sensor and road test the car. The Check Engine Light will most likely come on. If the car accelerates normally, that sensor is the problem. You can try to clean it. You will see small wires that look like a light bulb filament when you look through it. You can use air intake cleaner, or compressed air, or both. Make sure it is 100% dry before reinstalling and plugging it back in. Always connect/reconnect sensors with the ignition off. If cleaning does not fix it, the sensor will need replaced. Also check the air intake hose very thoroughly, especially between the MAF and the intake manifold. Push, pull, and bend it. If it is cracked, this can cause your issue as well.

The next thing that comes to mind is the EGR valve. If it is fully opening when you accelerate, it will cause a rush of "un-metered" air, and a hesitation. It should slowly open. The position of the pintle is monitored by the computer, so this not setting a code is far less likely. Perform the same test, unplug the connector and road test. The EGR valve will not be commanded to open when the transmission is in Park. You have to drive it. If this is the culprit, the valve will need replaced.

If one of these two parts is the not the issue, a more thorough test will need to be performed. A scan tool will be needed to check other parameters. If you would like someone to perform all of these tasks for you, a certified mechanic from YourMechanic can come to your home or office to inspect your engine’s hesitation issue and make any repairs that are needed.

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