Took my Chevrolet utility 1.4i 2015 model to dealer because it was missing. Dealer informed me that wrong spark plugs was fitted. They changed spark plugs and did a diagnostic check but could not find the problem. They said I must bring it back the following day. After a whole days wait I finally received vehicle back and now the idling is fluctuating between 900 and 1000 rpm. They thought it was now a mechanical problem and want to open motor to check valves. Also did a compression test that revealed problem with cylinder 3. I refused them to open motor. Took vehicle to trustworthy mechanic and he informed me there is a slight difference in idle speed but no mechanical issues. Vehicle preforms well on road when driving it.
Clean the throttle body and check for vacuum leaks. A fluctuation of 100rpm is not a big deal. though 900-1000rpm seems high, is that when cold? Warm should be around 700rpm on most vehicles.
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