On the phone this sounded like a simple problem, a Honda Civic Type R has a high idle when cold and is hunting badly when warm.
Got to be an air leak, Right?
The garage has performed a smoke test and no leaks were found in the inlet system. No fault codes are stored in the fault memory and there are no pending codes.
I performed a visual inspection, and everything appeared to be good, the vehicle had a full service history and had just had a service when this fault was mentioned to the garage. The symptoms were just as described on the phone, and once warm the vehicle starting hunting. A quick test ( I placed my hand across the throttle body-the engine stalled immediately) proved the smoke test was right the vehicle had no air leak.
The scan tool showed normal live data, and no DTC's. However the idle speed was not being controlled by the ECU correctly.
If there was a circuit fault there should be a DTC. This could be a mechanical fault with the idle speed control circuit. I removed the throttle body and ISCV this is the rotary type valve on this vehicle and a build up of carbon had resulted in the valve sticking. These valves can be stripped down and cleaned. This was down and the throttle body re-fitted. The idle speed must now be reset using the scan tool, and allowing the engine to idle once warm for 10 minutes.
The vehicle no performed as it should, proving the relying on DTC's is a big problem if the fault is mechanical.
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