Q: My car has some trouble codes and has a rough idle in reverse and drive but is fine in neutral and park.

asked by on February 14, 2018

The trouble codes on my car are PO420, PO300, PO304 and PO505. I do believe that the first three are in result of PO505 code. I have replaced the EGR valve, modulator, Vacuum switch valve, vacuum control valve, purge solenoid, new spark plugs and spark plug wires and boots and both engine coil packs(because of other codes. First I thought the Idle Air Control Valve was faulty causing these codes but when I did the test of testing the RPMs and unplugging the IAC my RPMs change, thus telling me that the IAC is not completely faulty. I read online that stated that if the IAC was faulty then the engine wouldn't shake and stutter in acceleration, which is another reason I took to believe that the IAC was not faulty. When I turn on the air conditioning, the car struggles and feels more so like the engine is choking, which again, makes it seem like the IAC is bad. I checked my EVAP hoses and replaced a couple of them but I am still having issues with the engine stuttering in idle.

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Hi Justin. Thanks for contacting us today. Trouble codes can be caused by multiple issues ranging from component failures or simply sensor or electrical harness connection issues. However, the best way to determine what is causing the codes is to analyze the symptoms you’re experiencing. This typically helps a professional mechanic determine what repairs are needed - as the codes are designed to simply be a starting point for resolving the actual issues. If your Toyota is having issues accelerating when the AC is on, this could simply be due to clogged fuel injectors, dirty throttle body or a mass air flow sensor that is clogged with debris. While the codes indicate IAC failures, the symptoms you’ve described typically don’t relate. You should probably have a professional mechanic complete an on-site inspection to help resolve your issues.

You may be correct in the first three codes may also cause the last one (P0505) to be triggered, which points to the IAC valve. You can test the functionality of the valve by checking its electrical resistance if you have access to an ohm meter. To do this, disconnect the IAC valve, connect an ohmmeter to pins 2 and 3 of the valve. If you get a resistance value between 10-14 ohms, it indicates IAC valve is working as it should. Next, connect the ohmmeter to pins 1 and 2. If you do not get a resistance value between 10-14 ohms, the IAC valve may need to be replaced. If the IAC valve is not faulty, you may want to check the MAP sensor as this may also cause similar type symptoms when putting a load on the motor.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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