It stalls at the light. Sometimes the whole fault is a film of carbon.

There is no fixed interval, because it depends almost entirely on how the vehicle is used. A car doing short trips in traffic, a delivery van stopping every few minutes, or a truck idling on a jobsite all collect deposits far faster than a vehicle that runs long highway stretches. In practice the symptoms are the schedule: when the idle starts hunting or stalling appears as you slow down, it is time regardless of mileage.

On an electronic throttle that is the move that turns a small job into a large one. Aerosol sprayed into the bore can strip a factory coating and run down into the motor and the position sensors behind the plate, and levering the plate open by hand strains the gears that drive it. A replacement throttle body costs many times what a proper cleaning does. Correct solvent on a rag, by hand, with nothing allowed to run inward, is the version that works.

Because the computer is still compensating for the dirt that is no longer there. It had learned to hold the plate slightly further open to keep idle correct with a restricted bore, and with the bore clean that same position now passes too much air. The adaptation has to be cleared and the make’s relearn procedure run. Done properly, the idle is right within minutes rather than after days of the vehicle sorting itself out.

It measures the air entering the engine, and it is easily contaminated. The most common cause is an aftermarket performance filter that has been over-oiled, which sends oil downstream onto the sensor’s heated element. Once coated, it reports less air than is really flowing and the engine runs lean, producing hesitation and a stumble that feel exactly like a dirty throttle body. Testing it is part of this job, because cleaning the throttle alone would not fix it.

No, and anyone promising that is guessing. Carbon at the throttle plate is a very common cause of hunting idle and stalling, but a vacuum leak, worn plugs, a failing coil, a contaminated airflow sensor or a sticking ventilation valve all produce similar complaints. Reading live data first tells us which one is in play. If the throttle body turns out to be clean, we say so and keep looking instead of cleaning it anyway.

It does not. The intake ducting comes off, the bore and plate get cleaned by hand, everything goes back with its seals seated, and the relearn runs off a scan tool. All of that happens in a driveway, a parking lot or a yard with the vehicle exactly where it already is, which is the whole point of a mobile setup for a job this size.