Had a very similar problem with my 98. Try driving with maf sensor unplugged. If it runs like normal thats your problem.

 

Fixed it!!!


No More Huge Fan noise under hood and no more power loss when engine is warmed up!!!


I after spending thousands of dollars on various sensors and repairs, fuel injectors, fuel pumps, etc. I went with this AC Delco Fan Clutch ACD# 15-4684, GM# 15154901


This part cost me about $90 and shipping.


The fan clutch was one of the items I replaced from the get-go, but used a different part/manufacturer and it cost about $40-$60 at the time. And my issue was still present


Once I installed the new Fan Clutch from AC Delco, the huge fan noise was present for about 5 sec, then dissipated. I ended up driving from Arizona to Denver the very next day (about 900 miles). Not ONCE did the fan/power loss issue surface......


My Truck stayed under 190 Degree entire way through!

 

Congrads! I can see how the new fan reduced the roaring noise, but how did the fan help the low power/no acceleratin part of it?

 

I believe the first time I replaced the fan clutch, it was either a bad one, or just functioned/engaged once the engine temp hit around 130-140 degrees. After knocking around the idea that the problem only occurred once the Fan clutch would engage at such an early temperature, I tried to think "How do we keep the Fan Clutch area COOLER?" The only conclusion I had left was to try a different fan clutch...

 

I know many are finding out that buying OEM aka AC Delco or Delphi up front is cheaper in the long run. It is hard to do when you are on a tight budget and you are presented with 'bargains' on the net /ebay. But I like doing the job once and not chasing around after an illusive trouble. Exp. when you thought you had fixed a problem with inexensive parts. Thanks for posting your search for the solution.