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Old 07-05-2009, 06:06 PM   #1
elitescouter
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Default My car shakes at idle, vacuum goes to -25 at rev... leak??

Ok so this started happening lately...

My car shakes at idle, when the radiator fan turns on the car allmost dies.

The vacuum at idle goes from -20 to -21 back and forth as it shakes

When I rev my car while stopped, the gauge goes from -20 psi to 0 then down to -25... I have never had my car go down bellow -21 psi when reving it while stopped.

What can my problem be? Thanks

EDIT: Added logged numers and graphs at idle. (Scroll down it's in reply)

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Last edited by elitescouter; 07-06-2009 at 02:59 PM. Reason: Added logged numers and graphs at idle. (Scroll down it's in reply)
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Old 07-05-2009, 07:12 PM   #2
Jim2752
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Can you still go into boost and besides the shaking does it still run fine? any weird sounds? Make sure your air filter isn't clogged up and check for an exhaust leak. I don't know if that could cause this but its not a bad idea to check anyway.
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Old 07-05-2009, 07:17 PM   #3
seekndestroy19
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probably vacuum leak. check all the hoses and hose going from "T" to boost gauge.
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Old 07-05-2009, 07:23 PM   #4
dye.sti
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my car idles around -23.5 vac runs fine and hits target boost. I dont think that its a vacuum leak.

looks like it may be something else wrong.

"My car shakes at idle, when the radiator fan turns on the car allmost dies."

This makes me question if its more of an electrical problem than a leak anywhere you car should not almost die if your radiator fan turns on.
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Old 07-05-2009, 07:27 PM   #5
vinxH
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start from the easy things first. check vacuum leak.

and im guessing you're not getting any CEL?
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Old 07-06-2009, 01:43 AM   #6
elitescouter
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No CEL's or pending codes
I do hit my target boost.
This all started happening after I used the flatfoot shifting that was put on my car. (It ran fine with it for a month or so and now this started happening)

Reseting the ECU doesen't fix it.

Maybe exhaust leak? Idk if this would cause it.
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Old 07-06-2009, 04:19 AM   #7
stierzy34
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Check out cleaning the MAF sensor as well as the IVAC. My car didn't act exactly like this but I did have trouble ideling and car almost dieing anytime I pressed the clutch in. Both of them are easy to do and work for me.
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Old 07-06-2009, 09:53 AM   #8
elitescouter
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Quote:
Originally Posted by stierzy34 View Post
Check out cleaning the MAF sensor as well as the IVAC. My car didn't act exactly like this but I did have trouble ideling and car almost dieing anytime I pressed the clutch in. Both of them are easy to do and work for me.
Allready cleaned the MAF with CRC MAF sensor cleaner like 3 weeks ago, its still doing the same thing.
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Old 07-06-2009, 09:59 AM   #9
scprs
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TPS sensor maybe?
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Old 07-06-2009, 11:10 AM   #10
rkramer
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Do you have a logging cable? i'm guessing you could probably post a log of your idle and it might help a little bit.

Also, vacuum isn't negative. Can't have negative psi. Vacuum is measured in inches of mercury, and always a positive number.
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Old 07-06-2009, 11:10 AM   #11
elevenpoint7five
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try raising your idle to 850 instead of 750.
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Old 07-06-2009, 02:58 PM   #12
elitescouter
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Here is a log at idle, the spike = radiator fan turning on.




Here are the values at idle.



If you see a problem =) let me know or if you need me to relog with another field that I have missed that's important.

Thanks
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Old 07-06-2009, 08:18 PM   #13
elitescouter
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Any ideas guys?
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Old 07-06-2009, 11:46 PM   #14
AraSh
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my engine is completely stock and my car sometimes shakes at idle too!
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Old 07-07-2009, 12:22 AM   #15
C-DAY
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my car does it 80% of the time a start up. Then it smooths out, the ecu fixes the problem there is nothing to worry about.
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Old 07-07-2009, 12:41 AM   #16
Miharu
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Do you have your A/C on?

Defiantly not a vacuum leak, they cause high idle.

Line 47+48 = relevant correlation between engine load and RPM, means nothing to a diagnosis. This sounds like a ghost, unless your A/C is on or turning on when your radiator fan turns on or something.

Has anything else happened recently that may be important like a large pothole or donuts or uncommon amount of miss-shifts?

Erroneous idle/ misfire at idle can be associated with neutral position switch. I had this and a MIL(CEL) came on and by using a professional scanner I cleared the code and its gone. (probably not the same thing)

How many drive cycles would you say you have gone through, it may take quite a few before a CEL comes on.
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Old 07-07-2009, 02:09 AM   #17
elitescouter
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Quote:
Originally Posted by Miharu View Post
Do you have your A/C on?

Defiantly not a vacuum leak, they cause high idle.

Line 47+48 = relevant correlation between engine load and RPM, means nothing to a diagnosis. This sounds like a ghost, unless your A/C is on or turning on when your radiator fan turns on or something.

Has anything else happened recently that may be important like a large pothole or donuts or uncommon amount of miss-shifts?

Erroneous idle/ misfire at idle can be associated with neutral position switch. I had this and a MIL(CEL) came on and by using a professional scanner I cleared the code and its gone. (probably not the same thing)

How many drive cycles would you say you have gone through, it may take quite a few before a CEL comes on.
No the AC wasen't on.

Not miss-shifts but i've been using the flat foot shifting that's been put on by a professional tuner with am opensource. I mean the car ran fine for a month or so with it. I did use the FFS allmost daily.

I went through couple of drive cycles.

Is there a way an exhaust leak can be causing this?

EDIT: I forgot to mention, it shakes less when its cold, as soon as it warms up thats when it starts.
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Old 07-08-2009, 03:04 AM   #18
elitescouter
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Quote:
Originally Posted by scprs View Post
TPS sensor maybe?
Do you think that TPS sensor can cause this?

If so, is it bad and needs to be replaced or just cleaned?
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Old 07-10-2009, 02:24 AM   #19
Miharu
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Quote:
Originally Posted by elitescouter View Post

Is there a way an exhaust leak can be causing this?

EDIT: I forgot to mention, it shakes less when its cold, as soon as it warms up thats when it starts.
exhaust leak as in a valve problem?

Can you look at live sensor data? That would show a bad TPS or anything else. Can you view or post Fuel Trim data? Can you run a 5 gas analyzer on it?

What happens at a high idle like 2500rpm?

Try some top engine cleaner and injector cleaner and see what happens...

Still sounds like a ghost that you might just have to live with.
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