So I fought with the idle speed motor from day 1 with my Monty-
always seemed like it was sticking, not working, etc
even after 2 ecu swaps and umpteen motors.

<edit- and found that this is the USUAL cause of poor idle-
only about 1 in 4 junkyard idle motors are any good! So make
sure your motor and ecu are working before you go further...>

Finally dug into the TB with a vengeance, and found some
things:

there IS a manual idle speed bypass, even though the manual says
there is not. It's under a lead plug. It has a LOT of range.
It may solve your problems with #2-

the warmup regulator. It's a thermostat, wax and all, that
allows significant bypass air when the truck's cold, and meters it
down to a little bit after it warms up. It's plumbed into
the throttle body heater circuit.
It also has a HUGE range of 'normal' operation, and thus
the bypass screw. The one on my truck was almost closed
at cold, and would shut by 150f. That left all the idle
on the ECU, and it just couldn't handle it. Of 5 junkyard
bypasses, it was by far the 'coldest'. Normal seems to be
mostly open at 70f, and almost closed by 212f. Some did
completely close, others did not quite. Almost all, except
mine, were mostly open at 70f. Mine was probably at most
25% open.

Yeah, there's nothing in my FSM about this part. At all.

#3 was hilarious- the 'don't touch it' idle screw wears a divot
into its stop, allowing the throttle plate to close further.
When I reset it according to the FSM, I think I added at least
2 turns...

#4 was common sense- clean your throttle body occasionally.

Also, the '89 parts are unique- the 90 and 91 parts
seem to interchange. This is par for the course with an '89...

So if all these things aren't right, the ECU just can't cope
with the idle air by itself. The FSM says it can, but given the
huge amount of air you can add via the regulator and manual
bypass, I don't believe it.

All that said, I haven't had an idle problem since cleaning
everything and putting in a different warmup bypass...
I used one that was 'way open' at cold, and didn't find a need
to add any manual air bypass to that.

Ideally, I suppose, you'd check your IAC at normal hot
idle and make sure it had travel left, but mine seems to
have settled in just fine as is.

hope this helps someone,

t

Toby, good write up.

How did you change the wax pellet air bypass? I thought it was made into the throttle and could not be changed unless you changed the whole body. I think there is one mention in the fsm that I've seen, but I remember it's in an odd place. Unfortunately, I can't remember where. The bypass closes very fast, too, based on observation of my 3.0's.

Good stuff...Mods put in Archive please.

Done. <img src="/forums/images/graemlins/kewl.gif" alt="" />

that is a great write up toby, ill be looking into mine when it get back above 0. so what propted the write up? did idle issue start with loping at idle? or was it a cold start issue? ive had a bit of an idle grimlin since my head swap and have been chasing it ever since.

The 1st gen (and maybe early 2nd with the 6g72)
have a separate bypass valve on the bottom of the
TB- it's held on with 3(or 4) long screws.
I'll try to take a few pics next time I go to parts storage.

This was something I'd had trouble with for years-
the truck would just stall occasionally when warm.
Sometimes it'd be ok, others it would be a real pain.
I tried various workarounds that often worked... for a while.
So last winter I got frustrated and went over everything-
and this is what I'd found.

I remembered a bunch of us had the same problems,
so I hope it helps.

t

pics would be appreciated... give me an idea of what im looking at since it isnt in the fsm.

I've never ben able to unscrew the H2O thing off the bottom of my T.B.. Is the wax thing accessable from the inside?
On the 24 valve 3.0 I can see where it's repairable.

My 89, 3.0l hits 2k right after start and does not change as it reaches normal operating temp. I have done everything I know to find a vacuum leak but nothing. I replaced the ICS, TPS and took the TB apart and cleaned it. I took the bottom off the TB and cleaned that as well. I did not see a wax anything. I did see a spring thing that the heater hose attaches to. So I figure that it is some sort of cold idle speed deal. Nothing I have done thus far has changed the 2k idle speed.

Should I see this wax or did my montero swallow it?

So I got a salvage throttle body and sure enough that did the trick. I now can control the idle. I still think it is mysterious that nothing I tried could identify a vacuum leak. Oh well.

Has anyone followed the procedure to set the accelerator cable tension. I have a chiltons type manual (I couldn't find it in the FSM I downloaded here) that has you get the engine normal operating temp, turn the key on for 15 sec and then place a feeler gauge ( I can't remember the thickness) between the SAS and the throttle and then tighten the throttle cable tension to that. I followed this and either I am doing something wrong or its whacked! If you do this the throttle never touches the SAS and the idle speed is elevated and not controlled by anything.

I am still having issues with the timing. Now that I can control the idle speed I set the timing. With the timing set the engine pings severely. So I had to set the timing by driving it and adjusting the timing until I did not get any pinging. Something is still not right. The engine is sluggish and does not have the power I know it used to.

I'm stuck.