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Old 10-09-2009, 01:30 PM   #1
97ebaygst
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Unhappy Rough idle! Think its dumping too much fuel I need help

I just recently purchased a 97 gst with 125,000 miles on it. When I bought it the guy that sold it to me said it ran real rough and that u could smell unburnt gas coming from the motor. When I got it home and pulled out the plugs they where black as could be. So to see what it would do I bought a new set of plugs and those blacked out after letting it warm up a little.
When I start the motor it has trouble starting. It'll turn, chug and repeat once or twice before it'll turn on. Once it's on it'll idle real low, like it's barely above 0 on the tach. When i try and rev it it'll jump like 500 rpm up then act like its gonna cut off before i take my foot off the gas. If I do this to or three times then press the gas slowly it'll crawl to between 4 and 6 grand before it sounds like it's backfiring and then bog down again.
I have done a compression test and it read between 170-180 across the board. I hope I did it right cause It was my first time doing it. Things I checked are the coil pack and the tps. The coil primary resistence read .3 on both leads. Where I read it said the norm is .75 anything else to replace, but it still runs, so I was wondering if the sence of extra fuel could be from the coil not firing hard enough to burn it all.
Thats all for now but if anybody could help me out i would be very grateful. This is my first turbo car so im a little lost on working on it compared to a n/a motor
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Old 10-09-2009, 02:06 PM   #2
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Re: Rough idle! Think its dumping too much fuel I need help

Sounds like it is gas fouling the plugs. Is the car throwing any cels? I had the same problem on my 98 and it turned out being that the cam angle sensor was going out. Check the cam angle sensor if you haven't.
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Old 10-09-2009, 02:09 PM   #3
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Re: Rough idle! Think its dumping too much fuel I need help

Sounds like you have a fuel injector that is stuck open, issues with your FPR, or problems with your Mass Airflow Sensor. If your car is in fact running too rich, it would probably come down to one of those three problems. I can not post in classifieds, but if you in fact find out you have bad injectors, PM me I have an extra set of stock 450cc I'm never going to use off of a 99 GST (I don't want to get banned from the forums, I'm just trying to help out).

It def sounds like you're running rich though. Have those things tested.
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Old 10-09-2009, 02:12 PM   #4
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Re: Rough idle! Think its dumping too much fuel I need help

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Originally Posted by forcdndukshun View Post
Sounds like it is gas fouling the plugs. Is the car throwing any cels? I had the same problem on my 98 and it turned out being that the cam angle sensor was going out. Check the cam angle sensor if you haven't.
Great point too, keep in mind if you're getting any spark, chances are it is firing hard enough. Timing and CAS could cause the symptoms you are having too.
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Old 10-09-2009, 02:13 PM   #5
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Re: Rough idle! Think its dumping too much fuel I need help

Um, first, what has all been done to the car?

Have you done a boost leak test? That could be a problem. http://vfaq.com/mods/ICtester.html
That will help you with the leak tester.

It could also be a fuel pressure regulator issue, or the coolant temp sensor.

It could also be as simple as huge injectors and no engine management.
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Old 10-09-2009, 02:13 PM   #6
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Re: Rough idle! Think its dumping too much fuel I need help

I'll make sure to check that out. Also i was just snooping around under the hood checking wires and stuff and i noticed that the coolant temp sensor pig tail is broken could that have anything to do with it even though its throwing fuel even when its cold?
It's pulling air intake temp sensor circuit malfunction and coolant temp sensor circuit malfunction.
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Old 10-09-2009, 02:15 PM   #7
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Re: Rough idle! Think its dumping too much fuel I need help

I know that coolant temp sensor will cause it to run in open loop and rich if it is out.
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Old 10-09-2009, 02:16 PM   #8
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Re: Rough idle! Think its dumping too much fuel I need help

Yes, that could be your problem. Fix that, then report back.
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Old 10-09-2009, 02:20 PM   #9
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Re: Rough idle! Think its dumping too much fuel I need help

I thought it was the injectors too but they r all black. But I'll still check it out and get back to u. Any body know where I could get a pig tail for that?
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Old 10-09-2009, 02:22 PM   #10
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Re: Rough idle! Think its dumping too much fuel I need help

Heh, I got mine from a buddie who pulled it out of a box of wires. Literally a 25" cube box of random DSM wires. It was funny.
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Old 10-09-2009, 02:29 PM   #11
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Re: Rough idle! Think its dumping too much fuel I need help

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Heh, I got mine from a buddie who pulled it out of a box of wires. Literally a 25" cube box of random DSM wires. It was funny.
if only I were that lucky. lol
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Old 10-09-2009, 02:50 PM   #12
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Re: Rough idle! Think its dumping too much fuel I need help

Try a junk yard in the area?
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Old 10-10-2009, 12:24 AM   #13
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Re: Rough idle! Think its dumping too much fuel I need help

I had the same issue wit my car could be the temp sensor....but for the blackening spark plugs I am clueless. It can also be the cam angle as stated befor. Maybe even your ecu.... I myself had that happen when my ecu was on its way out. Was the car in running order when you bought it?
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Old 10-10-2009, 11:07 AM   #14
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Re: Rough idle! Think its dumping too much fuel I need help

Ok guys I found a pig tail for the temp sensor and fixed that. I also changed out the cam sensor but it stills runs rough. It's better where it doesn't back fire or chug anymore but still low rough idle. I haven't taking it out on the road yet but now the gauge isn't showing any boost, I hear the bov opening but it's just not reading. I've heard that it doesn't build boost while sitting still but when i got it the gauge still read some boost. Did I disconnect something on accident?

After looking more into it I notice that he disconnected the wastegate actuator and the flap moves freely. I had my wife sit in the car and look at the gauge and rev the engine while i held the flap shut thinking that could part of the problem, but still no sign of boost on the gauge but bov still pops off.

So looks like i just added to my problems. I think i fixed part of the problem but still something there that i cant fix. Could the IAT code that pops up have anything to do with it? Well I'm gonna take it out for a test drive any see if it builds boost.
any help would be appreciated. thanks
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Old 10-10-2009, 12:49 PM   #15
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Re: Rough idle! Think its dumping too much fuel I need help

Could a bad knock sensor cause my problems?
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