Got a 2009 Sylphy 1.5 (non-CVT). Been having intermittent erratic idling when stationary and engine hesitation when accelerating; CEL light didn't come on. Spark plugs and air filter are newish and I clean the MAF sensor with CRC cleaner regularly. Brought to workshop (ex-Tan Chong staff) for checking but no fault codes surfaced. Swapped MAF sensor, filter, PCV valve but couldn't pinpoint the problem. What else could it be? Clogged injectors, faulty crankcase positioning sensor? Thanks for any help.