04 GT hanging idle problem.

LaserSVT

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#1

• Jun 15, 2009

• #1

I have been trying to help my buddy with this one problem but cant seem to figure it out.

When the car is warmer it hangs at 1600 when you stop (sometimes higher) and will idle around 1200-1500 all the time.
The mods:
C&L intake/upper plenum
PP T-body (not sure of size)
O/R H-pipe
Bassani Cat back
Diablo tuner
4.10s
Zex nitrous kit
MSD window switch
Fidanza Clutch

Whats been replaced searching for the problem:
Fuel filter
spark plugs
IAC
MAF meter

Now in addition to the idle problem the car falls on its face after 3500 RPM as well. It pulls well then seems to lose half its power above 3500.
It did this BEFORE the nitrous kit or window switch were installed. It does it with or without the Diablo tune installed. I have gotten it to idle ok by removing the IAC and setting the limiter on the throttle body to 800 rpm but the second the IAC gets pluged back in it jump up to over 1500, even if I have the t-body closed all the way (it will stall with the IAC off). The problem with removing the IAC is... well you all know the car dont run right without one so keeping it unpluged is not an option.

The car dose not overheat or blow smoke. No wetrd noises eaither. I am at a total loss. Any ideas? :SNSign:

 

stangnutlx

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Jun 15, 2009

#2

• Jun 15, 2009

• #2

Have you tried checking TPS and voltage? Maybe check MAF operation.

 

LaserSVT

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stangnutlx said:

Have you tried checking TPS and voltage? Maybe check MAF operation.

Click to expand...

Forgot, yeah he replaced the TPS and I checked the voltage. That was several months ago and I have forgotten what the voltage was but checking on here it seemed right. Also the MAF meter was reciently replaced.
I am wondering if its the C&L plenum or the t-body. Wish we had a stock one to swap it with.
Damn car is not setting off a MIL eaither cause I was thinking bad COP or two with the power loss at higher RPMs but wouldnt there be a misfire MIL?

 

S

swl987

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Jun 15, 2009

#4

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I had the hanging idle deal after putting on a accufab throttle body. It drove me nuts for quite a while. I did the tps and a bunch of other BS a bunch of times. Accufab told me as far as setting the butterfly inside the throttle body that you just put it up to light and make sure the light is even all around the butterfly at idle.There was quite a gap showing but I thought it was alright.Wrong. I showed it to my neighbor after a year of dealing with it and he thought there was too much gap letting too much air through at idle. The butterfly was a little crooked so I reset it and got the butterfly so there was just a tiny gap around the butterfly at idle. Now the car idles great and and there is no more hanging idle. I don't know if this will help you because your car is loosing power after 3500rpms, but maybe it will help someone else.

 

mr.shovels

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Apr 20, 2008

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#5

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A little more on it. The car has a hard miss to it from the passenger side. It now has an occasional ticking sound coming from the driver side drive train. It randomly decides to run right and strong. Also if I unplug the IAC the idle drops to about 800 rpm but randomly dies. It will occasionally start idling really rough and the whole car will shake.

 

LaserSVT

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Have you checked the cop boots? And all the coils are still stock right? I hate to throw parts at it like has always been done. You need to bring it back over so we can test the TPS again and go over everything.

 

mr.shovels

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I made sure all the boots were snug about a month ago. It didn't help at all. I took it by a mechanic I know to look at it. He wasn't sure what it was. But another thing it is burning really rich.

 

LaserSVT

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Wonder if the diaphram in the fuel pressor sensor is ripped.

 

mr.shovels

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I checked for codes using two different diagnostics scanners. They both showed no codes.
I think the car hates me.

 

squeak93

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Jun 16, 2009

#10

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Seriously check the butterfly on the tb as suggested above. I'm fighting a hanging idle a little bit still after polishing my t/b. I've had a hard to get it to idle at 1k. What I did, re clock the butterfly in the tb the best I can. Then I put a new iac and a restrictor in the line leading up to the iac.

To do that I simply took a 1/2 in brass screw on plug. I took an air tool and smoothed it round (got rid of the wrench points) and drilled a hole in it. I can't remember what size but it was around 1/4 (smaller if I remember). That has my idle at 1200 when cold then 900-1k at temp. That the best I can get it. It does hang for about 5-7 seconds when you roll up to a stop light but I just deal with it. I can't afford a new t/b as I"m sure it's my issue after polishing so I make do.

 

LaserSVT

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John, when can you bring it back by here? Pick up a new t-body gasket and lets tear her down and figure this thing out.
Or tell ya what, trade me for the Mark VIII

 

mr.shovels

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I can come by after I get off work at 3. Oh I took the throttle body off a month or so ago and cleaned it out. It was completely covered on the inside with oil

 

LaserSVT

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mr.shovels said:

I can come by after I get off work at 3. Oh I took the throttle body off a month or so ago and cleaned it out. It was completely covered on the inside with oil

Click to expand...

Cant today but mabey Thursday or any day after that.

 

squeak93

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mr.shovels said:

I can come by after I get off work at 3. Oh I took the throttle body off a month or so ago and cleaned it out. It was completely covered on the inside with oil

Click to expand...

Thats your problem. I imagine you used brake klean or carb cleaner. they take off a protective coating that is on the t/b. Never clean with anything that isn't coating safe (on a tb that is) Good luck.

 

LaserSVT

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squeak93 said:

Thats your problem. I imagine you used brake klean or carb cleaner. they take off a protective coating that is on the t/b. Never clean with anything that isn't coating safe (on a tb that is) Good luck.

Click to expand...

His aftermarket one dose not have the coating on it. Besides, it has done it since before then. I was the first one to clean it over a year ago and I looked for the sticker/stamp and noticed the insides were a flat appearence and not suedo shiney like the coated ones are.

 

mr.shovels

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I used throttle body cleaner to clean it out.

 

squeak93

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Then I've got nothing....

 

mr.shovels

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The only thing I can think of anymore is that it has a bad COP, causing the miss. But it isn't throwing codes. OR would a vacuum leak cause my loss in power and miss? Or how about a burnt valve? But what would cause it to run rich, the tuner has been taken off. It smells like it burning straight fuel

 

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2000GTHRSE

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#19

• Jun 16, 2009

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This maybe a little stupid but check the PCV valve, and check for vacume leaks. If there is a leak in the system somewhere that could cause the idle to climb too...just a suggestion

 

crazystang25

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Hook it up to somethin that can read your emissions like a modis scanner or somethin and check the o2 levels as well as co2 and hc's and CO. High o2 and hc's could mean misfire which would cause the power loss. Misfire could give that rich smell from unburnt fuel. Check your IAC count at idle then compare tp voltage to idle rpm. I would say a vacuum leak but it would take a pretty big one for a hard miss.
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