i had somthing very similar when i took my TB off to clean it on my 1.4L MPI, The revs would take along time to drop to idle, and even then it would tick over arround 1500-2000 and eventualy drop to 1000 if i left it running. I never figured out what it was but i ran the engine and pulled the vacuum hose off that runs the brake servo, the engine tryed to stall so i poped it back on and it was fine ever since!?
Worth a try! it worked for me
