You may not able to tell by idle. My car idle like stock with 264/272 hks cams due to a reflash. Yes, open the oil cap will let you know at least one cam is whether an upgraded or not.

Also, if the car keep fulling to red line before running out of steam then it may have cams as well.

 

even with a reflash, you should be able to hear a slight lope somewhere during idle. I dont think you can get it tuned so perfectly that you can't hear the cams. My 2 cents.

Nebo

 

Well! My EVO friends listened to the idle and they can't tell. Same as the technician at the local dealer. Yeah! I'm curious too that why I opened up the valve cover to check.

I'll not get into any debate over this subject. I just want to help the guy here.

 

ask the dealership to open it up. they have a shop with mechanics right? tell them you're not buying it unless you know what's in there. it isn't that hard. they'll do it just to make a sale.