CPU usage pegs at 66% when fans come on

I have a MacBook Pro 11,2. The "system" uses 66% of cpu with nothing else operating. I've wiped the SSD and loaded Mojave. Nothing else on the machine and activity monitor shows system CPU use of 66%. I loaded TG Pro to monitor the temperatures. It did not change the CPU use. Temperatures are all normal staying at about 45 degrees C. I noticed that when the fans shut off, 0 RPM, the system CPU use drops to 1 to 3% and my machine works as it always has. When the fans come back on, system CPU use again goes to 66% making the machine difficult to use. TG Pro shows the temperatures never leave the green zone. If I put it to sleep, CPU use goes to 1%. When it wakes, fans come on and CPU use goes back to 66%. Apple online diagnostic shows one error code, PPT004. The battery has been replaced with a third party product. The repair shop finds no problem with the new battery, and says the error code is simply a result of the battery not being an official Apple product. Activity monitor shows no CPU hogs. The highest use is by activity monitor, followed by bird (????) Activity monitor use ranges about 12%. With the system using 66% of the CPU at idle, the machine is darn near too slow to be useful. The CPU use seems related to the fans coming on, not racing fast, just on at 2000rpm. Any hint or suggestions?