Odd RPM drop

[LuckyX2]

Hey guys, I'm having a bit of an odd issue with my sr. At idle, after it has warmed up to about 145-155F, there is a sporadic droop in rpm. From the datalogging on the haltech unit I have, I can see that there is a sudden loss of some vacuum, the rpm drops as a result, injector time is increased due to the load change and it goes rich as a result. It idles around 14.5afr and drops to about 13.5afr as a result from all of this.

It drove wonderfully and had just put down 300whp but then I had made a 4hr trip and by the end I noticed the lurching at idle and it felt like it was doing it at highway speeds too, with an accompanied power loss. I did not push it at all during my trip, which was mostly highway; I doubt it even saw more than 5psi.

I'm thinking it may be due to something in the valvetrain as I've noticed it is noisier than usual. I had done solid lifters, tomei cams, titanium springs/retainers and new guides a little while back but recently has been my first time driving it, since I've been learning to tune my haltech. I had shimmed it all when it was done but a few were still slightly off due to tomei being out of the shim sizes I needed. Nothing seriously off however and I just haven't yet gotten around to re-shimming. I already pulled the valve cover and everything looks ok but I was unable to gauge the tolerances at the time.

Any ideas on possible causes? Thanks

[LuckyX2]

For anyone who cares to know, I took off the valve cover, removed the cams and discovered that a valve lock had gone bad on one of the intake valves for cylinder 2.
This caused the valve to jam itself up in the retainer, ruining the lock, valve and retainer.