Throttle Body Carbon Buildup and Idle Surging
ModerateFuel SystemOn 1.4 and 1.6-litre petrol engines, oily crankcase blow-by gases and exhaust deposits accumulate around the throttle butterfly valve and idle air control passage. Over time, the gummy carbon deposits prevent the throttle plate from returning to its precise baseline position, resulting in fluctuating engine revs, stalling when depressing the clutch, and hesitation upon accelerating from junctions.
Unstable engine idle speed that hunts between 700rpm and 1,500rpm, Engine cutting out unexpectedly when stopping at traffic lights or roundabouts, Sticking or jerky accelerator pedal travel under gentle initial throttle application, Illuminated Check Engine Light with diagnostic codes related to idle air regulation
- Remove the air intake trunking and check the throttle bore and butterfly plate for dark sticky residue
- Start the engine and observe whether the revs stabilize cleanly when blipping the throttle
- Inspect the idle air control stepper motor and associated vacuum hoses for splits or blockages