Jag Vanden Plas Check Engine Light and Pinging

I have a 2001 Jag Vanden Plas (4.0 v-8 with 85k miles) and recently been having a couple of problems. About every other week the check engine light comes on and remains for 3-4 days, then resets. I notice during this time that there is a pinging in the engine on acceleration. Also, on a couple of occasions, at freeway speed, the car will lose almost all power, but the RPM's remain high. Taking my foot on and off the accelerator eventually "fixes" this problem with a "bang" as the power re-engages. As you would expect, this causes the check engine light to come on. I recently had the timing chain replaced, but no other significant work has been done on the vehicle. Also, a couple of months ago, I got a check engine light and it was determined that the engine was getting too much air in the mix. I discovered that the air intake from the hood was loose and tightened that. Upon doing so, my mileage increased about 1.5 mpg to a blended rate of about 19-19.5 mpg. Because of the increase in mileage, I think the first check engine light is not connected to the current problem. But I'm no mechanic.