DOHC - Throttle body cleaning
Over time, oily carbon "blow by" residues build up on the throttle plate, restricting openings and gumming up sensitive moving parts such as air metering needles, or on the case of the Sierra DOHC EFi and 2.9 EFi V6 engines, the Idle Speed Control Valve (ICSV).
Carbon build up on the throttle and ISCV assembles predominantly leads to idle speed problems but can also affect throttle response and sometimes cause ragged running. Such symptoms are usually associated with CO (“idle mixture”) or ignition timing problems though this is not always the correct diagnosis and cleaning the carbon build up from the intake assembly can sometimes resolve these issues cheaply and effectively.
In this How To... I will cover cleaning of the throttle body and ISCV assembles.
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