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What's the best way to clean the intake manifold? Without removing for inspection, I'm assuming after 130k miles, it would be a good idea to consider...might free up deposits causing slow flap engagement and remove the assumed oil and dirt deposits that might occur outside the path of the fuel that cleans the runners...generally, the center section of the manifold doesn't get the spray down/cleaning like the runner do...Could we benefit from such a cleaning?

Also, has anyone installed an oil catch can in their rigs? I could see benefit from this more then any negative...I haven't seen any photos of such things so perhaps I'm misstating an assumption...

spitanddirt

I did have some pictures somewhere when I took mine apart. If you want to clean it right, you will want to completely remove the intake from the car. And even then your going to want to separated the upper and lower case halves of the intake to get everything out.

You will need two intake gaskets, a couple cans of brake clean, carb cleaner, cleaning brushes, and patience! You don't want to break any of the plastic pieces/flaps.

But.....the most important part is what to use to seal the case halves back up. I used Threebond 1211 sealant on the intake halves. This sealant is specifically designed for sealing these kinds of assemblies. It's used as OEM sealant on motorcycle crankcases. It's about $22 per tube if you buy it locally from a motorcycle dealership. It's slightly less thick than normal RTV from Permatex or Versachem/ITW, but it sets up very well.

THE MOST IMPORTANT PART IS TO LET THE THREEBOND SET UP FULLY BEFORE STARTING THE ENGINE. I think I allowed the sealant to cure for 24 hrs. I've probably driven at least 120k miles since I cleaned my instake so I can vouch for it's effectiveness.

Good luck if you attempt this yourself. It's not hard, but you shouldn't think that you can knock this out in a day. Removing the intake requires undoing some wiring harnesses and and pulling the fuel injector rail. With these cars nearing 20 years old, the rubber and plastic isn't very tolerant of movement. Just something to think about as you bend hoses and harnesses out of the way.

Threebond Link below

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Wow! Thank you for your in-depth experience...I was honestly hoping for a quicker/above the engine job like spraying a praying kind of work...but truly, do it right and do it once is always the best approach...especially on these cars. I have heard of folks using the MOPAR Combustion Chamber Cleaners with great success but I'm worried it might be "too good" and cause some of the tired plastics/hoses to let you know you shouldn't have attempted this like this... ( )

Regardless, when I do valve covers gasket and other such wearable parts, I will be sure to revisit this and use your advice...Thank you and when I do the work, I'll be sure to share the results with photos, etc....I know it's not a diesel motor but I'm almost hoping to free up more factory "umph" by removing some carbon that has accumulated...but perhaps I'm wishing for too much...Did you notice a lot of carbon build-up when you did this to your D2?

spitanddirt

Not as much carbon as I thought, but by freeing the stuck flapper valve shafts, you can definitely feel the extra oomph at 3000 and 4000 rpm.

BrianC72gt

The real issue with the flapper valve shaft is corrosion/pitting on the magnesium alloy bearing surface where the shaft passes through the front of the intake manifold housing. I've had good success loosening the two fasteners that secure the flange, prying it back a little, hitting it with spray lithium grease, working the shaft, then tightening it up. The bearing surface of the shaft is just some form of plastic. Pull the shaft out too far and the other end of the shaft all the way in at the back of the manifold will slip out of its bearing hole. Then you will have no end of fun trying to thread it back into the hole blind.

Those aftermarket arms are blingy, but serve no purpose. The problem is not weak arms, but rather a seized shaft. The only thing stronger arms will do is move the failure point to the vacuum actuator pods. If you can't crank the shaft levers easily by hand - seized bearing. Loosen the retainer tap it, wiggle it, exercise it, lube it and you are good to go.

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Awesome information you two! Thank you for the (future) help on this endeavor...

pocketchange

FWIW, I've been using MMO as a fuel additive for decades.
Stuck my Tele Tube (tv) viewer probe down the intake and noticed VERY little build up..
Went into a combustion chamber awhile back and had very little carbon build-up (almost NONE.)
I'm guessing the plenum is clean enough, since the flap seems to be doing its thing with my old 99' purring like a kitten.
A pint added with every oil change too...
pc

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MMO is good stuff...I'll be sure to replicate your trials to ensure it stays clean, etc...Thanks for the suggestion!

Verybumpy

Acronyms are the bane of our existence. What is MMO?

jfrahm

Quicker to google and have the answer than to ask and wait for a human to respond:
https://www.google.com/search?q=MMO fuel additive