I lived through a plenum failure on my '94 sr (after replacing the motor) and I never had a check engine light. That is until the engine seized.

Did you plug it in to a code reader before you took it apart? You might have another problem besides the vacum leak.

By the way, the only symptom I had prior to engine lunching was a wistling sound that I thought was coming from the a/c vents.

On a final note, I live in Ventura county & have a scan tool that works on both pre and post '96 Mits. It would be nice to know who else has similar units, and setup a sort of code reading/diagnostic network.

Clark

Is this a problem on the later SOHC 3.5's?

Nope, the engine light came on around midnight while driving home from Tahoe, I stop rightaway, and noticed the vacuum leak as soon as I open the hood, I remove the plastic cover that goes over the intake and notice the leak was from plenum rod/shaft. I just unplug the actuator and kept driving home.
I took it all apart last night and to my surprice the butterflies look pretty good, they are not loose or ready to fall in, however I notice some of the plastic bushings where the rod/shaft goes thru, are a bit worn out (not all of them though)
I was wondering if you guys know if this rod/shaft is suppose to have a bit of play, I mean if you were to grab it with your fingers and move it up and down, should it move a bit? how about back and forth? mine does! <img src="/forums/images/graemlins/confused.gif" alt="" />
I will appreciate if any of you guys with DOHC 3.5L engines can check the movement of this part! <img src="/forums/images/graemlins/cheers.gif" alt="" />

Also what exactly is difference between the new updated lower plenum and the old ones? <img src="/forums/images/graemlins/confused.gif" alt="" /> looking at the picture on tech section write-up, looks like the butterflies are still there!

As I understand the problem, the bushings wear, the butterflies start to flutter from the slack, and the heads of the butterfly screws break off, and the butterfly whangos the motor mechanicals as the engine tries to eat it. You should not have that much slack, so your bushings are goners. The new plenum is supposed to have diff bushing material and better strength screws, IIRC.

Ya, I don't remember my new plenum having any slop. And by the by my 3.5 was able to eat about 1/2 of one of the butterfly valves before it gave up the ghost.

Here is what I did some time ago. Rebushed the shaft with brass tubing from a hobby shop. Now have 184k miles on it.
http://www.4x4wire.com/forums/showf...;oldertype=&bodyprev=#Post710727

One more questions for you guys:
Some people are telling me that if I seal all the holes where the shaft goes thru and have the intake polished, I'll see a low-end performance inprovement??
Can someone explain how this works/happens? and how noticeable is it?
Sorry if it's a dumb question for some but I rather ask then be wondering! <img src="/forums/images/graemlins/cheers.gif" alt="" />

doubtful. Maybe some, but I do not think it would be enough to notice a difference.

I agree. However, polishing the intake runners does make a noticeable difference with forced induction. At the end of the day this is a 6,000lbs Montero with 200hp. You'd need quite an increase power to even notice. I reckon I can't 'feel' a power increase of less than 5 hp in my miata and I can feel every pebble on the road in that thing. If I could 'feel' a 2-3hp increase, someone should be paying my to drive...and they're not (I don't mean a taxi <img src="/forums/images/graemlins/lol.gif" alt="" />)

I think my earlier question got swamped. Should I be worried about this issue with my SOHC 3.5L <img src="/forums/images/graemlins/cheers.gif" alt="" />

Eddy answered it, sort of <img src="/forums/images/graemlins/lol.gif" alt="" />