1500 RPM Idle

Just acquired a new 5spd xj, and every so often (not very often) my RPM's will jump to 1000, 1200, and sometimes 1500 RPMS when the clutch is in, or when i'm in neutral. I think it might have something to do with the throttle body spacer the previous owner installed. Any ideas?

Also: its an 87 xj 2dr, 4.0 I6, AX15, 4x4

Start searching: TPS, grounds, bulkhead connector, Renx files, High idle, renix high idle, etc. This has been covered MANY times