irregular motor revving

Just changed the alternator out of my wife's 2001 PT. Started it back up and now the engine is revving up and down. Only going about 200-300 rpm's, but it cycling about 2-3 times per second. Going to check the hose between the air cleaner and throttle body today, but anyone have any other clues? Thanks in advance.

Just changed the alternator out of my wife's 2001 PT. Started it back up and now the engine is revving up and down. Only going about 200-300 rpm's, but it cycling about 2-3 times per second. Going to check the hose between the air cleaner and throttle body today, but anyone have any other clues? Thanks in advance.

Maybe you could try resetting the PCM by disconnecting the battery for 10 minutes? It sounds like an engine management issue?

Once it turned daylight again, the problem became pretty apparent. I had knocked a vacuum hose off while reaching down the back of the engine compartment sometime during the alternator swap. Runs fine again.