Why does my 99 z24 with 2.4 ld9 sound like a diesel at idle ? It runs great otherwise and has good get up and go, but idles around 650 rpm and sounds like a diesel. The noise is coming from the top end and fades with increase in rpm. It has a new timing chain kit with less than 3000 miles from PCI which included the chain tensioner, chain guides, chain, and cam sprockets. Sometimes at initial cold start there will be a brief rattle for about a second or two as well. car has 189k, but not sure how many miles are on the engine beause it seems that it was replaced at some point. The engine has a heat tab on the coolant bypass tube indicating that it was under warranty at some point. The car doesn't seem to get very good gas mileage in the city, about 16mpg, but gets about 28 on the highway. It's a 4 speed automatic.
