my son and you have the same problem but it's intermittant and so far tough to get a meter on. He immediately replaced the fuel filter, plugs and wires and rotor and cap. next the engine coolant water temp sensor and now a throttle position position senson (TPS). unless we have two problems, this problem of ours started with a slight drop in RPMs (10-20%) At idle and once in a while while on the highway.It was so slight a drop at that speed momentum covered the problem. We immediately thought about fuel problems, then the ignition system and now into the least expensive possible sensors that are listed in the Trouble Shooting Guide in the Factory Service Manual <fsm>.(2nd link on main index on this site).
We started with the Engine Coolant Temp Sensor because of a previous minor loss of engine coolant,the rough idle and loss of power when under load issues. Now on to the Throttle Position Sensor (TPS). Both around $100. My sons recently purchased hid truck. It's rust free, stock equipment and now on a Maine island doing lobster fishing work. With a rebuilt engine (fire under hood when truck had 100K miles).Presently 140K with lots of life left. So far we just can't catch a code while in the shop. To the lobsterman his truck is comparable to the farmers tractor. Not looking forward to the mass air sensor ($700+). Next step to the Dealership (90 minutes away). Trying to avoid it till after the fishing season (6 to 8 wks). We'll see.
I'll keep watching your thread and sharing on mine. 22RE