I just put a new vortec 350 in my 96 Chevy and the truck starts and runs but when trying to dial in the timing I’m having some issues. I tried the standard procedure of installing the destributor and leaving it just loose enough to where you can move it by hand for adjustment. Then I raised the rpm to about 1500 and used a scan tool to attempt to set the timing to the recommended range. As far as I know I did everything right but when using the scan tool (I tried 2 different ones) the degree of tkming changes every one to two seconds while the destributor isn’t moving and the rpm is consistent. Any ideas what might cause inconsistent timing? Just FYI it’s not the distributor being loose I even tried tightening it all the way and no difference. Maybe ecu problem? Thanks guys.