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Discussion Starter · #1 ·
Hi there, just wanna say hi to everyone, new to the forum here. International student from Malaysia currently studying in ASU, Tempe, Arizona. Glad to see a whole community of car lovers! Just got my eclipse a few months back and now I need to change my intake plenum because of a vacuum leak.:mecry2:

Anyway, just wanted to ask a quick question. I've been searching online and on the forum but didn't get a very clear answer so here goes, what is the difference between an intake manifold and intake plenum?

2003 Mitsubishi Eclipse Parts - Mitsubishi Parts | OEM Mitsubishi Parts | Genuine Mitsubishi Parts

Is it just upper and lower? I'm looking to buy a replacement and the price difference between a new and used one seems to be quite high. Should I buy a used intake plenum or should I just go with the savings on this part? $1000 is pretty pricey for a repair as I'm only a student. If anyone could advise me I'd really appreciate it. Thanks guys!
 

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Welcome. Before I would consider dropping a thousand bucks on a new intake for a vacuum leak, fix the leak. Unless the shaft ( I assume you are referring to the butterfly shaft seal) is physically broken, this leak could probably be fixed for a couple dollars. Remove the seal and take it to you local Bearings and Drives or Motion Industries have them match it up. Should be able to do this without even removing the upper intake.
 

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Typically Manifold and Plenum are interchangeable words to describe the same thing. Do you have the V6 (GT or GTS)? Before getting to throwing parts at a problem, first diagnosis where and what is causing the vacuum leak, it my be as simple as a bad gasket or loose vacuum line which are usually it 80% of the time. First do a good visual inspection with a flashlight of the lines to make sure they are firmly connected then try starting the car and while its idling, spray some carb cleaner around the lines, intake, etc and listen for a change in the engine's idle. If it changes when you spray a certain spot you found the leak. Now if you actually need an entire intake manifold/plenum, your best bet would be to find the nearest junkyard, go in and find another 3G and take the manifold from it and just clean it up or have a shop port and polish it.
 

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Discussion Starter · #4 ·
Hey, thanks for the reply. yea I think it is the butterfly shaft seal that is leaking and apparently my mechanic said it isn't sold separately so I would have to buy a whole new intake plenum for replacement. I'm in the process of buying a used one though.

Welcome. Before I would consider dropping a thousand bucks on a new intake for a vacuum leak, fix the leak. Unless the shaft ( I assume you are referring to the butterfly shaft seal) is physically broken, this leak could probably be fixed for a couple dollars. Remove the seal and take it to you local Bearings and Drives or Motion Industries have them match it up. Should be able to do this without even removing the upper intake.
 

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Discussion Starter · #5 ·
Typically Manifold and Plenum are interchangeable words to describe the same thing. Do you have the V6 (GT or GTS)? Before getting to throwing parts at a problem, first diagnosis where and what is causing the vacuum leak, it my be as simple as a bad gasket or loose vacuum line which are usually it 80% of the time. First do a good visual inspection with a flashlight of the lines to make sure they are firmly connected then try starting the car and while its idling, spray some carb cleaner around the lines, intake, etc and listen for a change in the engine's idle. If it changes when you spray a certain spot you found the leak. Now if you actually need an entire intake manifold/plenum, your best bet would be to find the nearest junkyard, go in and find another 3G and take the manifold from it and just clean it up or have a shop port and polish it.
Yea that's what I thought but if you click the link I posted it shows both the I take manifold and the intake plenum as separate parts. I did try and identify the leak with carb cleaner. Vacuum lines are okay I found one leak at the plenum gasket. The other one is deeper in on the drivers side of the I take plenum. Mechanic said it was the butterfly shaft seal. I have the GTS btw. Trying to buy the plenum from playamono whose parting out his gts.
 

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Well if its the butterfly then like a previous guy said you can try that. But its sounding like the gasket between the upper and lower intake manifolds and/or the lower to cylinder heads gasket. Full gasket set is like 10 bucks...and a good day if its your first time doing it.
 
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