I just changed the intake manifold gaskets,put everything back together right,marked the distributor while taking out,put back the same way.I fired it up and the Yukon 5.7 has like a rough idle and sort of a hitching under 2500 rpm I hooked a diagnostics tester to it and the code read 1345 and I dont have a guide to identify codes.What do you think???

Check compression in each cylinder., sounds as if it might be piston rings.oil thins as it warms so the drop in pressure seems to point to loss of compression .i take it it doesn't blow smoke out of exhaust?

no vehicle type,so I will be general.start by taking pictures of engine,this way you can put it back together,right.then mark all the hoses and electrical lines with pieces of tape so you can match them back up were they go,mark both sides of the lines at the disconnection points, take notes too..then start at the top and work your way down removing everything that is in your way.if you have any doubts take more pics so u can reference them on the reinstall.get new gaskets were needed,do not use old gaskets or you will create problems you don't want. u should have several bolts on both sides of the manifold make sure you torque to the right specs on reinstall,you find the specs on line just type in exactly what you want <torque specs,list make and model,and year,for manifold>.hope this helped

sounds like u advance the distibutor

Turn the engine over and bring #1 piston to the top of the cylinder then remove the dist. cap and be sure the rotor is pointing to #1 plug wire in the firing order. Turn the oil pump shaft with a screwdriver so you can keep the rotor pointing to #1 in the firing order set the dist. You have to pay close attention when you set the dist to the oil pump shaft or you can get it a half tooth off and car will backfire when you start it. Good luck

The 2.2 is known to "strip" the timing gear. The cam gear is made of a synthetic material. But...you could possibly have an injector bad on #1.

If the RPM's are going pretty low to where the car seams like its about to die, then it could be a vaccum leak. Whick could be cause by a bad gasket or something maybe didnt get sealed right when putting everything back together. If you do decide to change the gasket, i would recommend the "Hondata Intake Manifold Gasket". Its thicker and not made from metal and also keeps your intake manifold cooler.

Sounds like he got some plug wires crossed in the process

All chevy v-8s required distributor removal to pull the intake.

You do not have the dist. in correct or plug wires are crossed. Please check wires 18436572 is firing order.

Check to make sure you have the firing order correct. If so, go ahead and remove each wire to isolate the misfiring cylinder. From what I can understand from your post, it seems that so far, you have done everything correctly. Did it run well before you did the gasket? Running rich can be a product of a vacuum leak as well. To find it, spray some carb cleaner around perimeter of manifold, and near any vacuum source. If idle changes, that's where the leak is! If its leaking from the new gasket, you might consider, loosening up the bolts and re-tightening them in a cross pattern, side to side, beginning at the center, working towards both ends. split the torque value and tighten twice: if value is 30lbs, do once at 15, the second time @20. I hope this helps.
Good luck