Buick 3.8 Intake Manifold

Hello everybody
I have posted before about coarse idle 2001 LeSabre. I have replaced the spark plugs and wires with quality items, and have run three
consecutive tanks of fuel with either Lucas or Redline injector cleaner. My on board computer shows I now average 26 mpg, up from 22 mpg when I got the car less than two months ago. So I am happy with that, but my idle quality has not changed. I notice this engine uses a plastic, or composite type intake manifold. How can I tell if it has a crack, or is leaking in some way? Idle quality does not differ cold or fully warmed, so I have pretty much ruled out a vacuum leak. But I suspect the manifold, is this fair? I assume the fuel pressure regulator is the rather small device on the front of the engine toward the right with a vacuum line attached. I did remove the vacuum line, and even with the engine running no sign of fuel, could it still be causing my problem?
Thanks for any help! I appreciate the community here.
Scott
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When our 1998 plenum decomposed, it happened suddenly, although I guess the leaks could be slow in some cases.
Wife noticed it leaving a friends house and drove it a mile or two. Running rough, etc. Had the codes read at an Autozone and got multiple misfire codes.
I had been expecting the thing to go, so took it straight to the garage and parked it inside. When the mechanics tried to start it the next morning, it was hydrostatically locked. In total, we had driven it less than 10 miles when it went from a miss to a lock.
They replaced the defective device with an improved design and we have had no more problems to date.
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I have a 98 Park Avenue and I have the same concern about a potential intake manifold leak. Here's what I do: With the engine cold fill the coolant overflow tank to the upper (hot) level line on the side of the tank and keep a close watch on it. I check mine about once a week or so. If you have a leak the coolant level will drop over time. Also, periodically, I send an oil sample to BlackStone labs for analyis. They provide a detailed report which can highlight problems including trace amounts of coolant in the oil. The cost is $20. You can get all the info from their website. There was recall on the the fuel pressure regulator but it was for the diaphram which would leak. Since no gas came out of yours I assume it isn't leaking. I wouldn't jump on the intake manifold right away for a rough idle. You didn't say how many miles are on the vehicle. I suggest you look at other possibilities first. I would also have it scanned with a good scanner to see if any codes are stored. Hope this helps.

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You responded: "but my idle quality has not changed. I notice this engine uses a plastic, or composite type intake manifold. How can I tell if it has a crack, or is leaking in some way? Idle quality does not differ cold or fully warmed, so I have pretty much ruled out a vacuum leak. But I suspect the manifold, is this fair?" If you have thoroughly ruled out a vacuum leak, then you have also ruled out a vacuum leak occurring with a cracked intake manifold, which can also cause the rough idle. At this point, it would be good for you to check the fuel pressure at the injectors and ensure it is within specifications. Then you could determine if the injectors are all firing by using a simple noid light, one at a time, on each injector. (This merely verifies the receiving of electrical pulse that is supposed to open/close the injectors--not whether the pulse is adequately long or that injector is actually opening/closing 'properly'. You again cannot beat a proper scan which magnifies and demonstrates proper diagnostic patterns to pinpoint which injector(s) is not operating PROPERLY.) You could also properly pressurize the coolant system to determine if there exists an intake pressure/coolant leak. If one is detected, then determine its source. If it is caused by a leaking intake (seal) you should find it either seeping to the outside and dripping/running onto the ground or into the crankcase and engine oil. Either one should be easily seen. Depending on where this coolant is going, it possibly could cause a coarse idle--like if it going thru the combustion chamber and affecting the fuel/air ratio. Oh! Be sure to check the tailpipe and ensure coolant is not exiting thru the exhaust system via a leak into the combustion chamber. This should show up as excessive, white, steamy exhaust on a relatively warm and non-humid day. After all these possibilities, it sure would be nice to have it properly diagnosed by someone with technical experience AND technical equipment. Counting your time alone, it may be much 'cheaper'. s
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Excellent advice!

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I have a 97 Camaro with 3.8 Aluminum intake. Intake gasket leak. It went real quick after an overheat. It did not show temp as overheat either. GM just made some crappy stuff. It caused millions of intake leaks. I am having it fixed but bought another car also. Marquis with the 289 engine gets 24 on hiway. I believe if you average out the repair costs verses a reliable engine and gas costs the bigger engine will come out on top.
This is why the big auto makers are loosing ground to the Japs. Hondas and toyotas are just better built. Period.
sdlomi2 wrote:

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