new engine acting strange

1989 Toyota Pickup
After replacing my engine with 214K miles, my new engine has a strange behavior. It idles at about 600rpms and slowly climbs to about 1400rpms,
then suddenly sputters and drops back to about 600rpms. This repeats forever until I figure it out or turn off the engine. lol lol I'm thinking an emissions/vacuum problem, but I don't really know where to begin.
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Check the level of your engine coolant. Mine did the exact same thing when I changed the water pump, and didn't have the engine coolant full yet.

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... check your water levels... if your coolant is low your engine will rev back and fourth... freaking your sensors out... and why get a new engine if the old one only had 214K? It's just breaking in lol.... my 93 just turned over 300K Jodi
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