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Discussion Starter #1
when i start the car the idle is anywhere from 300-3000 rpm untill i rev it over 3000 then it's fine. such a stupid car!!!:banghead: :p i love it though:banana: any help would be greatly appreciated.

btw its a 92 4.9L pre northstar engine:)
 

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You need to check your codes....It'll most likely tell you what's up!
 

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Since you didn't mention a CEL (Check Engine Light), I'm going to assume that the computer won't offer much if any help on this issue. You're probably looking at a "mechanical" issue such as a binding throttle cable, or IAC (Idle Air Control) solenoid. Maybe even a dirty throttle body (which can bind the throttle blades).
First thing is to remove the throttle cable from the throttle body and try to evaluate what is holding the throttle open (if anything). If the throttle appears to be on the throttle stop screw and the idle is still racing, the IAC is the culprit. It allows air to bypass the throttle blades and thus control the idle. This is the same as the idle control circuit on a carburetor.
Binding in the throttle body and IAC is usually due to carbon build-up. This is usually why these items are cleaned at tune-up times.
 

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2005 CTS-V, 1994 Infiniti Q45
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I would clean out the throttle body anyway. I think its a good way to make things run smoother. And its not that hard, you can clean some, if not most of it, while it is still in the car. Also, if you do take off the TB, you may get a rag and reach inside where the TB is. Ill need a second opinion on this, because on my Q it is always a good idea to clean the plenum when the TB is off. Some people take off the plenum, but I dont think that is necessary.
 

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I didn't even think about that!.....Teach me to post at three A.M.!
 

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Eastern time buddy!!! I posted at 9am my time.

I have learned from my rice boards that having a clean plenum and throttle body can increase horsepower by 10-25 hp. Not only that but increases gas mileage, throttle response, and makes the idle lower.
 

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Im not sure about that either, that is just what i heard. It still wouldnt be a bad idea to clean it out.
 

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White Diamond 2001 STS
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They don't even know what the word "plenum" means. Ask 'em. They'll say, it's the pipe that goes from my Iceman filter to my upgraded 35mm throttle body.
 

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Actually most people arent modding Qs very much, and the engine is pretty sensitive to changing things. You could spill something on it and it wouldnt run right until you wiped it off!

What is your definition of plenum??
 

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When you say "plenum", it's usually referring to the intake manifold -- especially when they're in pairs, like an upper and lower. We used to have a 5.0 Mustang and we put a LOT of GT-40 parts on there (Ford Motorsport brand), including a new "upper and lower plenum".

I think on your Q45, it'd be easy to distinguish. That large silver spider-leg lookin' piece on the top is probably an upper plenum. It's probably bolted to a lower piece, called the lower plenum. So when you think about it, when someone says they like to keep their plenum(s) clean to boost power, you need to ask them if they really actually remove the intake manifold every now and then to accomplish that. :)
 

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Thats what they say to do!!!!!!! They want you to take that damn thing off, which has 400 little connections and hoses, clean it off, and replace all the hoses underneath it! Maybe takes 20mins to clean, but 5 hours to take it off and put it back on!!! I have been contemplating cleaning it, and will probably just reach my hand in there (skinny arms :D ). I think they intentionally make it complicated so people cant work on it!!!

Also, they go into great detail about cleaning just the UPPER plenum. The lower one is apparently impossible to get to and/or doesnt need cleaning as much. I may be wrong, but i think the EGR circulates into the upper plenum, and most of the gunk is inside there.
 

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I was thinking while reading your post about the EGR (and then I seen you make mention of it). That's true -- you would stand to gain some mileage and power from cleaning out any coked up EGR passages in the upper plenum.
 

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Where are the EGR passages??? They said its not too hard to clean them by sraping it out, but it could be hard if you dont know where they are!!!!!!!!
 

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I don't have any idea on a Q. That's a VH45DE engine -- go Googling for that and you may find something.
 

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Ill be getting the service manual soon, I just wanted to know if it was semi-universal?!
 

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Discussion Starter #19
it's in the shop now. i'm driving my grand mothers 1987 olds delta 88:rolleyes: took it to my cousins shop. he's good with gm's:D a message came up saying. low oil pressure..next screen.. please turn engine off. i shut the car off right there. :banghead:
 

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Ive never heard (cant say seen because I havent been in a sts) message saying please turn engine off!
 
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