01 running rough cold

[stroke it out]

So im working on my dads boss's tow truck which was running really rough on a cold start. When you first start it up it lopes for a few mins then smooths out a little bit. after the truck warms up to temp it will run just fine. I know its not the injectors. truck has 270k and has the reman stamp on top of the injectors. It was throwing a p1316 code and our genysis scan tool will not do a buzz test on this truck. So i suspected it to be a loose uvch. He told me to go ahead and replace all the valve cover gaskets and harnesses. So i did. soldered the outside harnesses to the wires. It had been sitting for a week before i got done with it. Got it started up and loped again for a few mins but didnt seem as long. Now when you give it a lil bit of throttle the check engine comes on then goes off when you release the throttle. Could a faulty idm cause a scan tool to not be able to buzz test? Im stumped please help.