After a heavy rainstorm my 2010 Tacoma has started to start up running rough first thing in the morning like its not running on all cylinders. If I...

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Customer

After a heavy rainstorm my 2010 Tacoma has started to start up running rough first thing in the morning like its not running on all cylinders. If I let it run for a couple minutes, shut it down and restart it's fine for the rest of the day.

Last updated
Elixir Cada
Toyota Mechanic

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Posted
Elixir Cada
Toyota Mechanic

Hi Gary,

Below are the most common symptoms of vehicle that runs rough during cold start. Parts that need to check/replaced are also included there. 

  1. If the car starts when cold but, idles rough or does not want to stay running, this can indicate a problem with the engine temperature sensor. When the engine is started cold, the engine temperature sensor sends a signal to the DME control unit to provide a richer mixture. As the engine temperature sensor starts to fail, it sends a higher than actual temperature signal to the DME control unit. The DME control unit leans the fuel mixture thinking the engine is at normal operating temperature. This causes the engine to run rough. As the engine warms, it not longer needs the richer cold idle mixture and the engine runs smoother.

     

  2. If the car idles rough this can also be indicative of bad plug wires, distributor, or rotor. One way to check for bad plug wires is to inspect the plug wire runs with the car running in a very dark area. If the plug wires are bad you should see some arching to the cylinder head or fuel rail.

     

  3. If the car idles rough or cuts off at low RPM or idle, the cause could be a failing O2 sensor. The Osensor is out of the loop at full throttle and will not affect the way the car runs.

     

  4. A rough idle can also be caused by a problem with the air flow box. The damper for the air flow box can fail mechanically or the contacts inside the box can get dirty and send a errant signal to the DME control unit. This can sometimes be corrected by cleaning the electrical contacts inside the air box. This requires removing the cover on the air box which is held in place by caulk. You will need to cut through the caulk and gently pry the cover off. Once the cover is removed, clean the circuit board inside with a good contact cleaner. When you have finished cleaning the circuit board, reattach the cover using a non-corrosive caulk.

     

  5. If the car experiences a rough idle or idle fluctuates several hundred RPM, this can indicate a sticking idle stabilizer valve. Many people have removed and cleaned them but, this is normally a temporary fix and the valve should be replaced. A faulty O2 sensor can also cause RPM to fluctuate at idle. Unplug the Osensor and see if the idle still fluctuates.

Let me know if you have further questions. 

Posted
Customer

I've also noticed the rpm's won't increase if I depress the gas pedel

Posted
Elixir Cada
Toyota Mechanic

What about the engine? Did you hear the engine revs when you press the gas pedal?

Posted

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