John Gill Commentary 2 Kings 17:33

"They feared Jehovah, and served their own gods, after the manner of the nations from among whom they had been carried away." — 2 Kings 17:33 (ASV)

They feared the Lord, and served their own gods
Worshipped both:

after the manner of the nations whom they carried away from thence ;
the Israelites, whom they had carried captive from Samaria; they worshipped the Lord in their idols, as they did, who pretended to worship God in the calves; so they worshipped the supreme God in and by their idols, and made use of them as mediators with him.