GM DOHC motors can be very particular on the plug wires you use. What makes them susceptible to problems on these types of motors is the sleeve design. If it is a two piece design, sometimes the charge/spark can go through that joint, into the cylinder head and going to ground. You can tell of your plug wires are the issue by pulling them and noting any carbon tracking at the joint of any two pieces of the sleeve.
However, his surging has nothing to do with ignition. If he was having a misfire issue that was a count high enough to trip the count trigger in the PCM (one or two misfires randomly aren’t uncommon and can be normal at idle on some GM engines), will also trigger DTC P0300 “current misfire code” and then the corresponding cylinders it’* happening on. I.E. if it was cylinder three, you’d be seeing P0300 as well as P0303.
Since he’* not getting any DTC’*, it can’t be ignition. It’* either on the fuel side or in the EVAP/emissions system as noted above by searching for vacuum leaks.
Aside from checking hoses and vacuum lines, make sure any piece AFTER the MAF is secure and sealed. Even the tiniest crack between the TB and intake plenum that can allow unmetered air in can cause a surging issue. So make sure all gaskets between these pieces look ok, and that parts are torqued to the correct spec, effectively sealing and leaks.
Have you had an injector cycle test? You’ll need access to a TechII to do it. But you hook a fuel pressure gauge up to the end of the fuel rail, hook the TechII up, run an injector cycling test. What the TechII will do is run each injector at a set interval, sequentially, while you watch the pressure drop on the pressure gauge as each injector fires. Most fuel rails run in the 30 – 40 psi area (+/- some), so if each injector as it fires drops it 5 – 10 psi, that should be a normal pull. If some pull 30 psi or none at all, you’ve found your bum injector. Go about there remedying the situation.
Of course these PCM’* can be very tempermental too. Are you sure your EGR and Secondary A.I.R. system are working? Although if they weren’t, you’d be getting their DTC’* also, usually a P0410 or P0430. Otherwise, it could be a bad mapping in the PCM.
Have you tried an idle re-learn? Go to www.obdII.com
or maybe it’* www.OBD-II.com
, I can never remember. There you will get the entire process as well as driving procedure for the most effective “re-learn”. This process is akin to re-booting you home PC after it’* been running for a week or more. It clears all the bugs and cobwebs out and resets it back to the base programmed mapping.