Got some work done, now I've got more issues
 

Hey everyone!
First off, I apologize if this is not in the right spot, it's been a long time since I used this forum.


So not long ago my check engine light went on because the Camshaft position sensor on bank 2 died out in my 2004 Enthusiast. I didn't notice any issues with the way it drove except very occasionally getting a slight rumble and low RPMs during idle and sometimes didn't like to start on the first crank.
So I got the code, bought the parts and had my mechanic replace it. Spark plugs also needed to be replaced as the others were very old, though they never gave me issues.

Well after having both sensors replaced and having the plugs and coils replaced, I picked my car up and it was so much worse off than it was before going into the shop.
It'll be driving perfectly fine but, seemingly whenever I'm in an incline (Even while parked) my RPMs drop to about 500 and the car starts a pretty rough rumble, far worse than anything before. And any time I revved up, the RPMs would tank out again in an instant rather than going down gradually.

That first day, I took it on the highway and anything over 3k RPM, the check engine light would start flashing and it was getting almost no power.
I took it back to the shop but because the Check Engine light wasn't on since the car decided to behave that day, we weren't able to get a diagnosis, though we did scan for issues. It came back with nothing.
I've tried driving it around enough for it to start acting up and take it back to show my mechanic but it always does it at random times so, thus far, I haven't been able to.

I'm trying to get a rough idea of what may be wrong.
I've looked around and I've found a few different sources claiming it might be a faulty spark plug and since I just replaced all six, that makes sense for one or more to be the issue.
But before I drop any extra money into it I thought I'd maybe get some opinions.
The car is pretty low mileage - 74k or something like that as it's just my weekend driver.
If any other details might be relevant let me know. I am, admittedly, mechanically inept so bear with me.

Thank you for taking the time to read :)

Hard to say. Could be a bad ground, loose wire, faulty new cam sensor, or faulty spark plug (s).

Try to have someone with you in the car with a scan tool and try to throw the CEL and get a code.

Oh, my apologies I forgot to mention that we did scan for issues to see the code but it came back with nothing.

As for having someone with me, outside of my mechanic, I don't know anyone with the proper reader but that is an option.

What brand and model of spark plug did your mechanic use to replace the original NGKs? BTW- the "very old" plugs were built to last 100K, so replacing them with another brand or type of spark plug can result in worse drivability. Also, some aftermarket CPS units have been known to malfunction in our VQ engines.