Just drove my '90 3.1L cross-country and it ran like a champ. Once I got here, I changed the oil, oil filter, and air filter as a little thank you for getting me here without a breakdown.

Yesterday, I got read to take a trip out of town. Again, ran like a champ. The engine hit 160-180 deg about a mile out, then abruptly lost power and started chugging like a VW bus with a bad carb. The engine surged quite a bit without moving the accelerator. It wouldn't go past 25 mph on perfectly flat ground, wouldn't accelerate at all rapidly, and backfired twice. I left it for the day, went to get my second vehicle, and made a parts run.

Started up the car this morning. Ran perfectly, to my surprise. Knowing I might have a short window of opportunity, I managed to make it to a place I could work on it. I replaced the plugs, wires, cap and rotor.

Went for a test drive. Felt like I had some power back that I hadn't felt in a while. Stepped on it hard to see what she'd give me, and once I got half way to the speed limit, she abruptly went to chugging just like before. I made it the 3-4 mi back to the shop, at 20 mph with hazards on. Again, she'd just warmed up... just past 160 deg. On the way back, it did go back to normal for about 5 seconds before crapping out again. The engine was probably 150 max when it did that.

Next on the list is a new fuel filter. I'll see if the techs at the shop can help me check the fuel pressure, but with it being so intermittent, abrupt and consistent with temperature, I doubt I'll be able to get it to do it on the lift. The fuel pump is less than a year old, so I'm, doubting that it's the pump.

Need diagnostic ideas.