90 camry sudden idle problem

[V6yota]

ok i have a '90 camry that was in great shape when i found it about a week or two ago, ran fantastic, i decided to pop out the stock air filter and put a k&n style cone filter, no immediate problems.....the next day i was cleaning the negative battery terminal and after i was finished went for a drive and found the car to drop down into 2-400 rpm range when coasting or comin to a stop......whats the idle range for the 90 v6? and what may have caused the sudden idle problem?...