Greetings all. I'm a little frustrated and upset about this, the blue tick is not running right. I had the egr burn out my intake and hydro locked my car. I replaced the upper and lower gaskets. New PVC sensor (MAT??) cleaned throttle body, i did remove all sensor before spraying and cleaning. New plugs and wires. I now get a p300 code and can hear a noticeable skip especially with the ac running. I replaced the coils and ignition module from the junkyard and no change,runs the same.sprayed throttle body cleaner all around and over my vacuum lines to check for a leak no change. Kinda bummed out i love my ride but hate this new issue any help or suggestions? I had no issue till the intake failure. Check engine light is flashing and p300 is my only code. It'* a1996 park avenue 3.8 vin k

How old are the plugs and wires?

New plugs, new wires.

Sorry, don't know why I missed that.

Well, obviously we already know its a misfire on all the cylinders. You already replaced the typical misfire culprits such as the plugs and wires. Another cause of misfires is a leak between the gaskets. Hows your coolant level? Even if the coolant is fine, you still could have an air leak (mis-aligned gasket) cause a P0300.

Or, there is a VAC line not connected somewhere.

would this "misaligned gasket" be discoverable by spraying air intake cleaner or something that could reveal it? or what would reveal this possible gasket issue?

It depends on where the leak is at with the gaskets. Sometimes the leak allows coolant to be sucked in and that will cause a misfire. But assuming the gaskets were installed correctly, sometimes a vac line is not connected or is broken. Retrace all steps taken when everything was taken apart.

i would think a vac. leak would create a high idle effect or hissing/whistling. it runs great just a skip that is very pronounced motor sounds good no knocking, rattling. ??

If its big enough, it will. Only advice I can offer is to go back and recheck everything you touched.

looks like all gaskets are good.i compared the edge of the gaskets and they appear to all be aligned plus all bolts went through the holes correctly since the edges are even. so im going to assume they are right. all vacuum lines are attached and not cracked or leaking.my coolant level is good, not losing any. will change oil again tomorrow . i will do a compression check in the morning.

checked compression got 165-175 lbs. all plugs are firing,coils are firing as well.checked and wiggled all wire connections and wires, checked all vacuum lines no leaks. did put hand(gloved) over exhaust pipe felt a slight but noticable suck back. sticking valve?? but that would have showed up i the compression test right?? anyhelp or sugestions. before start up after upper and lower intake gasket change i did drain the /antifeezemixed oil, put a bout 3 qurts of kerosene in engine and turned over with no plugs then drained, dumped some cheap fresh oil in turned over as before and drained. then replaced oil filter and put in oil and started and ran for about an hour thats when this issue showed up. have since drained and replaced oil one more time just to make sure its as clean as possible.