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Discussion Starter #1
So I found a vacuum leak and now the car is back to a normal idle. Thanks again for all the input from my other thread.

Now, after taking the car out for a test drive, the CEL light is on and it is very sluggish when I give it gas. The code from autosone shows the o2 sensor... Would that cause it to be that sluggish? and even casue it to shift from 1st to 2nd gear sluggishly? (If that is even a word!)

I already have a stock downpipe and Cat from my 2001 grand prix that is an exact fit, and figured I would replace the O2 while I swap that out. Is there anything else I should be looking at??? Again, the MAF sensor was already replaced about a month before it started acting up...

Thanks again guys!
 

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what was the exact phrasing of the trouble code? I noticed that anytime there is a check engine light on they say o2 sensor. If you don't know what it said exactly find out both the number & the description. You can then google the code number to find out what repairs to do.
 

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Discussion Starter #3
I don't remember right off hand the exact code... The car has 149,000 miles on it and it is the original Cat. I have been reading how common it is for these cats to go bad, and there was a TRB on them for 10 years or 120,000 miles. Obviously I am past that. Ha!
 

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How many miles were on that Pontiac the cat came off of? Make sure you replace the gaskets & also it's a good idea to use new fasteners to make sure all is well. I can see what you are saying, but it would still be a good idea to check the code information to verify what the issue is. Better to be safe than sorry & it doesn't cost any money to have the code rechecked & jot down the code number & description.
 

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Discussion Starter #5
Only 40k on the cat from the Pontiac. I am going to replace the gaskets and the upper o2 sensor as well. After doing that, I will reset the codes and then have the codes checked again if they come back on or if the cat doesn't fix the problem. Hoping to get it all done this weekend so I will post results... maybe it will help someone else down the road.
 

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usually if you have a sluggish O2 sensor code, that O2 Sensor is bad, but if you have an exaust leak before the sensor is will also set off that code
 

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Discussion Starter #7
Replaced the Cat and the upstream o2 sensor... car runs like new! It is amazing that a plugged Cat can make the car run that bad!

Word to the wise... my Cat was plugged so bad that the car would not go over 25mph. I found out the hard way that trying to drive it like this over to my friends garage was a VERY bad idea. The heat that the this produced actually melted a small hole on the air intake manifold. I was able to use some of the plastic mold and some jb weld to seal it up. This repair was much more involved than the Cat and o2 sensor replacement...

Thanks to everyone who helped me diagnose the problem.
 

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Congrats on fixing the car. The reason why the car would run so poorly is because with a plugged convertor the engine cannot breathe. All that exhaust has to go somewhere but it has a hard time when there is a clog in the exhaust. With that it stays in the engine which causes it to not burn the fuel properly, if at all. The engine has to work harder, therefore causing higher underhood temperatures. My guess is that is why that air intake part melted.

Did you replace the downstream o2 as well? Probably would be a good idea to since it can go bad like the upstream sensor.
 

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Discussion Starter #9
Downstream o2 sensor was replaced in December of 2006 so I thought it was ok. I took it out and inspected it, and it looks fine... a little discolored but not burnt to hell like the upstream was.

Now I am having an inssue with the coolant level... the "low coolant level" light is on. The actual levels appear to be fine. Last night when I got home, I let the car cool off and then filled the actual radiator with fluid cause it was a tad low, but nothing major. But then again this morning, the light came back on. I am wondering if there is a problem with the thermostat, or maybe even the heater core needs to be flushed out.

Plus the Transmission issue that is in my other post...
 

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Discussion Starter #10
Well I checked the coolant level when I went out at lunch and it was low again. But I also noticed coolant on the side of the motor, which I did not notice last night in the garage. Also in the garage, I did not notice any coolant on the floor from the leak but I am sure it is there. This tells me I have a blown intake manifold gasket... Sound about right???

This does seem highly likely with it being a known problem, as well as it having almost 150k miles on it, also from the cat being bad that I already replaced that was causing some major back-pressure and heat... Thinking I will also replace the thermostat at the same time.

I found a website that has the entire gasket set, including a new intake manifold, for $100... http://monsterautoparts.com/CHEVROLET/IMPALA/chevrolet_impala_intake_manifold.htm
 

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get these LIM gaskets they hold up better
http://www.zzperformance.com/grand_prix/products1.php?id=290&catid=103

also check your coolant elbows (at LIM & Alt bracket)
http://www.zzperformance.com/grand_prix/products1.php?id=370&catid=103
if you really want to fix the problem you can find a L26 UIM (aluminum) from a 06 lucerne or 05+ GP and put that on there, but you MAY need a TB adapter (also avail thru ZZP)
If you stay w/ the dorman/stock UIM grab a HVII from zzp to "wake the car up a bit" ;)
 

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Discussion Starter #14
did the work this weekend and all is well now, no leaks. The elbows were fine. I replaced the intake and gaskets, spark plugs, the thermostat, and the idle air control valve. Bad part is, now the "check engine light" is on... So I am going to see my friend at lunch today to see what the code is. Will update after.
 
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