Just to be clear, I'm not talking about bypassing any emissions equipment on purpose, more the opposite. I was looking at an 88 Trooper with 2.6L for a friend of mine who said it wasn't running very well. Actually I saw him in it and made the comment that it sounded like it could use some work myself. It won't idle cold, just dies, and once warm it wants to idle up around 2k. First thing I noticed was that the smog pump had been yanked off, probably quite some time ago. The big hoses are there and hanging open, but I couldn't see any other vac lines open. Since this was a 5 minute parking lot inspection, I didn't have much chance to look it over that carefully though.

What I'm wondering, is could having the smog pump just yanked out cause the poor idle, and rough running when it is cold? I'm used to working on my 86 with a carb, so the smog pump can come/go without making any difference other than the emissions. Does the air inlet line on the pump pull air from behind a sensor, and could having it open cause the motor to get more air than the sensors know about?

If it seems likely enough, he could just get a new/used pump and see what it does. For that matter, would the smog pump from an 86 with a carb fit and work on the 88 2.6L motor? I have a spare parts 86. I sort of recall there being some differences between the belt driven stuff on the 86 vs the newer stuff.