Lumpy and Stinky Idle.

[Tiger_kpt]

These are the symptoms I have had recently on my FD RX7. UK spec 1993.
 
Rough idle which gives off a very potent stink or smell. Idle hunting.
 
I have been reading around the net and have heard that this could be caused by the airpump or an O2 sensor? But can\'t find any details on this. Just wondered if someone can help with it or add a bit more info about the two relating to this problem?
 
Car is standard bar: -
 
ARC super induction box.
Magnecor leads - running 7\'s as leading and 9\'s as trailing.
Downpipe and deletion of the pre-cat.
Racing Beat cat-back exhaust.
Pettit Racing AST.
 
Running standard management.
But will be uprating to Apexi PFC before the weekend.

[Tiger_kpt]

Just out of interest... where is the electrical connector for the airpump? I may try disconnecting this (disabling the airpump) as well as firstly checking that the connection there is OK before I go any further.

[Tiger_kpt]

The airpump never operates at high engine speeds. Only at low engine speeds and idle. This operation is controlled by a clutch.
 
Can the clutch on these airpumps ever go faulty? So that the airpump never comes on?
 
Reason I ask is that when the airpump is removed, people complain of a lumpy stinky idle. Which are the symptoms I am experiencing. Although my airpump is intact as is my main CAT.