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Problem keeping power to the engine

I drive a 5 speed 4.0 L 1999 Jeep Wrangler. Sometimes when I’m accelerating, idling, or just holding speed I will lose power. It’s as if I had the clutch pedal to the floor then released it into gear, except the rpms decrease instead of increase. The rpms will bounce around for a while. If the transmission is in gear the Jeep will lurch forward on the up bounce of the rpm meter and do the opposite on the down swing of the rpm meter. Shifting up and flooring the gas pedal seems to fix it for a while. The problem comes and goes. Some days I don’t have the problem at all, others the problem keeps coming back. I took it into the shop and was charged 600 bucks to change spark plugs, cables, have the air idle speed and throttle body serviced. Of course none of them fixed the problem and the shop can’t figure out the problem. The check engine light is not on. Any ideas for things I can check without having to take it into a shop?

I would like to see that the engine manifold vacuum is within specs along with a compression check.

Is hooking up a data recorder a possibility with your vehicle? I would like to see just what is going on when the engine starts bucking.

Has anyone checked for TSB’s? perhaps a PCM reprograming exists

I wonder if this engine could be losing its timing advance some way.

Unfortunately, the only way I would be able to get that information would be to take it to some shop somewhere. And I honestly don’t know anything about a car’s computer system. Is taking it into a shop my only option for getting this fixed? Or are there other avenues I can check and hopefully find something I can fix?

I really would like the data I suggested. You could get the compression and manifold vacuum figures on your own. Someone helpful could check for TSB’s. It is only the recorder data and the timing advance data that is shop directed.

There may be “pending” codes stored in the computer even though the check engine light isn’t on. Possibly it’s something simple though, like the ignition coil.