Toyota: 2007 Toyota Matrix, throttle position sensor, 2007 toyota matrix

Question
QUESTION: I just bought a 2007 Toyota Matrix and today the engine light came on. Diagnostic showed code PO116 which has to do with engine coolant temp. My car will rev when idling and the lights go dim before the rev.  Are these related and any idea what could be causing this.  Thank you for your time and hopefully your response.

ANSWER: Hey Corrina,

In case these 2 are related by any chance, the fault could be with the ECU (Electronic Control Unit) which consists of the Engine Control Module and the Transmission Control Unit. In this case, I'd suggest you to take the vehicle to the dealership and have the ECU reprogrammed please.

However, the alternative phenomenon might mean a faulty throttle position sensor. It is situated next to the throttle valve and will have to be replaced.

Thank You.

Yours forever,
Sriky.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your reply and it turned out there was a recall on the ECM which has been replaced.  However I still have the problem when the defrost is on in my car the car revs and lights dim.  From the outside of the car it sounds as if a fan keeps kicking in and the mechanic from the dealership, where I bought the car keeps saying it's normal.  When I turn the heater on towards the vents or feet, the car doesn't do this.  Can you please help me once again.  Thank you for your time and expertise.

Answer
Dear Corrina,

What you witness here is actually not a defect, but forgive me for saying, an under powered engine. Whenever, you switch on the defrost, the AC compressor gets on, and the ECU increases the idling RPM of the vehicle so as to compensate the load of the compressor. However, the ECU would be limited to increase the RPM only to a certain extent. The older the engine gets, lesser the power derived to manage the compressor; which explains the lights dimming. However, when you turn the AC mode to feet, the air velocity from the vents are lower and reduces the load, which in turn can be managed by the regularly idling engine.

I know the above explanation doesn't resolve your concern, but i hope to get back to you with a counter measure at the earliest.

Thank You.


Yours forever,
Sriky