Hyundai Repair: coil pack/ vaccum leak, throttle position sensor, intake manifold gasket

Question
I have a 2001 Accent. I had a major vacuum leak. I took it to a independent mechanic who told me it was the intake manifold gasket. I could see where the gasket was split. Since the gasket is covered under warrantee, I took it to the dealer. They told me the problem was not the Intake gasket but the PCV hose and throttle position sensor. I replaced those parts and the car is still running poorly. Computer scan says misfire on cylinder 4 and multiple misfire. The dealer recommends I change the coil pack. I don't have the money to go chasing problems. I imagine it could also be an injector right? Is there any DIY way to isolate the problem? Is it difficult to change the coil pack? PS. I have brand new plugs and 5,000 miles on new wires. According to the computer scan the vacuum leak is gone. I appreciate the help.

Answer
The coil isn't difficult to change.  It simply bolts onto the cylinder head with several 12mm bolts.

Most misfire problems are caused by the secondary ignition system (plugs, wires, and coil in your case).  The fact that you have a #4 and a random misfire code complicates the issue, however.  For now, concentrate on cylinder #4.  Start by removing the wire from the #4 plug and then just place the wire back on the plug without snapping it back into place.  Then start the engine.  Now, using the wire boot, gradually pull the wire off the plug.  The spark should continue to jump out the end of the wire onto the plug (or whatever else is closest).  If it exits the wire or coil anywhere else, the place of exit is the area of defect.  If you find no problem there, then try swapping the plug with another cylinder.  If the misfire moves, then you know the plug was the problem.  

I've seen certain poor quality brand plugs and wires cause problems very soon after installation, so I think you shouldn't immediately dismiss them as causes.  It's also possible that the misfire could be caused by a manifold gasket leak, by an injector issue, or by an internal engine problem resulting in lack of compression.

Also worth mentioning is that the computer cannot detect a "vacuum leak."  The best it can do is say that it believe's it must supply more fuel than it thinks should be necessary (code P0171).  If this code is indeed gone and your fuel trims now show normal values-- you'll need a scan tool to view the values-- then I'd say the dealer has repaired the vacuum leaks.