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.

Nope, the air pump is there to inject air in to the exhaust
stream to get fresh air to the catalytic converter and to
dilute the exhaust before it reachs the atmostphere.
It helps the converter get hot quicker and helps keep it hot
so it can do it's job. It could have an effect of the
running of the engine, because it's above the O2 sensor, but
generally, it doesn't affect it that much.



The intake side of the pump has a hose that goes down
to a noise muffler (about 1¢" in diameter) that clips to the
side of the air filter box. The outlet side of the pump
has a hose that goes directly over to the distribution tubes
that direct the air to the exhaust ports on the cylinder head.

Thanks for the info litnin. I do know what the pump does and why it is there, it is more a question of what else goes wrong if someone takes it out and leaves the hoses hanging.



So can I take that to mean the inlet side of the pump is ahead of the airflow sensor and having that hose open is not letting unmetered air into the intake? I suppose it would have to be, since the air going into the pump never makes it to the intake anyway.

On the exhaust side, there isn't much to worry about other than exhaust leaks if the check valve on the AIR rail is bad. That just leaves the vac switching valve and any small vac lines that could be hanging open to look for.

No, you don't have to worry about that at all.
The intake for the pump is not drawn from the air filter box.
The hose that comes from the intake port on the pump has a
little noise and air filter on the end of it and it just clips on to the outside of the air filter box.