Engine noise- stuck lifter?

[phrogs]

Maybe that's my ticking sound as well, shows up out of nowhere and I can't figure out where its coming from sounds like its under the plenum on mine as well.

The problem is I just replaced them damn coil packs last summer.

[1991 Corvette ZR-1]

Just armchair quarterbacking the issue, but the rev to 3K rpm seemingly resolving the issue, to me, indicates an oil pressure or quality issue. The result is a ticking lifter or lifters. Does the actual drivability of the vehicle seem different? From a cruising perspective, or moderate acceleration, a failing coil pack will not allow you to maintain anything close to the performance you were familiar with before the issue developed. Unhappy ticking valvetrain will, it will just sound like a sewing machine from hell.

A bad or failing coil pack?s performance should not improve with increased demand in revolutions from air, fuel and now the significant increase in spark production demand from idle to 3K.

Furthermore, the heat generated from a cold idle time to a fully heat soaked motor from idling while diagnosing the issue should have an adverse impact on the failing coil capability to clear up when revved. You mentioned sludge on the distick, despite newer oil being changed in. If you can ohm the coil packs cold and hot and they check out, an oil change may be an easy option for next step.

With fresh oil, a few short drives SHOULD completely resolve the ticking lifter. If that is the case, something is in that pan that is compromising any oil put in over time and the valve train is not happy.