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Courtesy of John Mastriano
Click here for other issues which can cause rough idling on the 3.5 liter engine
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The original gasket tends to crack and leak at about 50 to 75K miles. This creates a masive vacuum leak and the engine will run rough and skips . It only needs to be replaced when it leaks but it happens often. I wrote these instructions for a person who found me on the board so I wrote them like an article and figured you could use them.
Intake Manifold gaskets(lower)
Note: Be careful when handling the fuel rail as not to put excessive force on it at any time
Note: When installing the intake air plenum , be sure to catch the four center bolts and the two side bolts (stiffener brackets) before tightening , The center bolts should be torqued to 250 inch pounds .The fuel rail bolts should be torqued to 100 inch pounds .
JohnAutoTech unequivocally stated the best way to do it. That is with rtv, quick hands to stop the fluid drip, not letting the rtv set too long, use mopar fluid, and having the car up on a rack. He probably has great tools also.
With all respect to JohnAutoTech, I lack quick hands, a car rack, any skill in squeezing rtv from a tube, and have no patience for scraping gasket sealer from the pan or transmission while laying on my back. I found using RTV frustrating and switched back to gaskets. I like to change the fluid twice each time and reuse the old gasket for a few days until I can get around to the second change.
Yes, I am careful about watching for leaks and the gaskets can leak. Just wipe a paper towel around the back of the pan to check for leaks. I have changed fluid in Chrysler trannys since 1988. Changing the fluid is the key to avoiding $1200 repairs like the one I faced a few years ago. Try not to glue the gasket in place it needs to move or it might leak. Some gaskets have a few smaller bolt holes that hold the bolts in the gasket and keep everything aligned while you put it on. Don't overtighten the bolts either.
Fram filters just don't seem to click into place and hold like Mopar or Purolator filters. For the record, this is not just my imagination. I have done a side by side comparison of both and there is a difference.
Watch the rubber O-ring. It is critical to the operation of the transmission and will set an error code if missing or misaligned.
One advantage I do have is that I can let the minivan drain overnight and get more of the fluid out each time.
Conclusion: RTV gives a better seal but takes skill to do right. Gaskets can leak but any car nerd can probably get it installed decently. If you use a gasket watch for leaks not just in the beginning but as the gasket ages, hardens, and shrinks.
Finally, respect JohnAutoTech. I learn something new each time I read one of his responses. He knows what he is doing.
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