Car is 2000 Corolla with 60k miles that sometimes has a low idle (sometimes) when driven for the first 15 minutes early morning. Especially when accessories turn on, the RPM drop suddenly to 600 and recovers to 623 then back to 650rpm. After 15 minutes, everything works fine (normal 650 rpm)…my guess is the IAC Valve/throttle body needs cleaning.
What exactly do I need to tell me mechanic? That both the IAC Valve and throttle body needs to be clean? Also, after “cleaning it using a spray”…should he wait till the “spray dissipates”? What happens if it goes inside the engine?
Just tell him that the engine is hunting when cold and let him suggest the cure. Just like going to the doctor, describe the symptoms not the treatment.
You should have no concern about the ingestion of the throttle body cleaner into the engine because it burns very nicely. In fact, it makes a great starting fluid for small engines.
One thing I noted about your intake system is that the Mass Airflow Meter is ibefore the tube going to the throttle body. So the mechanic will have to connect the tube up to the throttle body before the engine will start. Usually, I do the IAC cleaning with the engine running so I can exercise the valve i.e. go from Park to Drive to neutral to Reverse and turn ‘ON’ and ‘OFF’ the A/C compressor to check the operation of the IAC. Sometimes I will hit the IAC a second time to clear out any loosened goop.
I concur the IAC is probably the first place to start. But after that, are there any maintenance items suggested in the owner’s manual that are behind schedule? Problematic spark plugs, air filters, fuel filters can also cause this symptom. Ask the shop to check for diagnostic codes from the ECM too.