Teach me: Manifold Tuning Valve

[HawkeyeScott]

2007 Chrysler Pacifica Touring 4.0L V6, 43K miles. Thrown the Manifold Tuning Valve position senseor code (P2078) three times in the last month.

I've have some degree of understanding what an MTV does. But I don't know enough to grasp what could be wrong with it.

Probable causes on the scanner readout are:

-Linkage stuck or broken.
-Mechanical condition.
-Intake Manifold Tuning Valve.

Is it similar enough to a throttle body that it has perhaps gotten gummed up and needs cleaning? Or is it more like a Throttle Position Sensor with a plunger that might need replacing?

There is very little info. on MTVs out there. Parts store websites don't even list MTVs. Repair manual mentions them but says little else.

Any guidance would be great. As always, knowledge is power. Thanks.

 

[440Magnum]

It depends on the exact design, but usually MTVs are more like a throttle (butterfly valve) than like a idle speed controller. What they do is divert the air flow in the intake manifold through additional runner length at certain RPMs to boost torque- for example they make the air take a long path at low RPM so that the runners are tuned to help force the air into the cylinders. Then at high RPM it flips to sending the air through shorter runners for higher air-flow and better scavenging at high RPM.

They can get sticky and the actuators can go bad. I'd try cleaning it first, then dig deeper if that doesn't fix it. In this case, it could just be the sensor that's telling the computer if the valve is actually moving, not the valve itself.

I would suggest that you check the LH forums and the LX forums for some help. Remember that those cars have the 3.5L v6, which is identical to the 4.0 except for displacement.

 

[mechtech2]

440 is right.
Manually check the operation of the valve and vacuum diaphrams.
If there are solenoids, of course dive into those.

It may not be getting a signal , even though that parts are OK.
Maybe a vacuum gauge 'T'd' in on a long line inside the car while driving may help.
but first, make sure things move smoothly and freely.

 

[HawkeyeScott]

Thanks guys. I was sort of hoping the two of you would weigh in.

If something has fouled up to the point I should replace it, any iodea what an MTV costs? (And it looks like it's a dealership-only purchase?)

 

[swalve]

If it's a position sensor error, there's probably some kind of electrical wire at the valve that might just need to be reseated.

 

[HawkeyeScott]

Update: This light keeps going on and off. Drove 200+ miles yesterday and didn't see it at all. My wife gets in this morning and it comes on.

Just for grins (or frowns), I called the dealership to see what a new MTV runs. It's $200. Most interesting thing they told me was that they've never sold one of those for my vehicle. Never even stocked one. That tells me they don't go wrong too often.

The thing is, there's no noticeable difference in performance when the light is on vs. off. So does that mean that the MTV may not really be malfunctioning, and as mentioned above it could be a sensor? Or is an MTV malfunction even noticeable?

I thought I could remove the MTV but it turns out I can't. Bolts too hard to reach (brake fluid resovoir and oil fill tube in the way). I was going to see if it's gummed up and not able to move freely. May have to ask my mechanic to do it.

Any more ideas would be great.

 

[mechtech2]

Dig online, at the library, or even a dealer for how your particular system works.
Maybe even get an expensive shop manual.
Then you can test the wiring, connections, and individual pieces yourself.
This is an option, if you choose to go this route.