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Old 07-04-2011, 09:56 AM   #1 (permalink)
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Bad EGR valve? 2003 Impala 3.4L

Hey guys,

After taking care of all of the major problems with my Impala (LIMS for example), I've started to work on the smaller problems (rust, slight rough idle, etc).

I recently purchased the OBDPros USB scan tool. I decided on this one mainly because of the double buffering and firmware upgrade capability.. so I can keep it for a long time and still use it with newer vehicles.

My car has had this.. "whistling" sound when idling, it slightly changes with RPM, but I can't hear it when driving - it's probably drowned out. I also can't seem to hear it from the engine bay, which may also be because it'd being drowned out. I know there's a TSB on this sound, which describes how it is likely due to porosity in throttle body. I don't think porosity in the throttle body would cause what I found out below:

So... arrive the scan tool. At idle, my Short Term Fuel Trim ranges from 0-3, and my Long Term Fuel Trim stays around -14.1. Intake Manifold Absolute Pressure stays around 10.3 inHg, MAF stays around 0.54 lb/min, Ignition Timing Advance for cylinder #1 stays between 19-20. Idle RPM ranges from 650-740. When I say my car has a rough idle, I don't mean the engine sounds rough or the car shakes badly. But, the car shakes every 2 seconds. It's hard to describe but doesn't seem normal. Based on what I've been reading and the scan data I have.. it seems like I have a vacuum leak (MAP at 10.3 idle?), and the car is running rich ((Well, before being corrected by the FTs) LTFT at idle being -14) but I could be wrong.

Here is some data I graphed of a short drive:


I just have a feeling it could be the EGR valve based on what I've read.. but I was wondering if anyone here had any ideas. LIMS have already been changed and this whistling/"rough idle" was occurring before that.

Thanks and sorry if something like this has already been posted that I missed :).

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Old 07-07-2011, 07:09 PM   #2 (permalink)
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I hate to bump.. but does anyone think I have a vacuum leak of some kind, and if so should I worry about it/any ideas where it might be?

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Old 07-08-2011, 04:41 AM   #3 (permalink)
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I was going to say it sounds like a possible vacuum leak... 9 times out of 10 i think the EGR would throw a code?

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Old 07-08-2011, 11:31 AM   #4 (permalink)
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map is low, should be around 16 iirc
MAF increase w/ throttle right?

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Old 07-08-2011, 04:08 PM   #5 (permalink)
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MAF does increase with throttle.

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Old 07-12-2011, 08:55 PM   #6 (permalink)
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So any ideas for what I should check? Maybe I could record the "whistling" sound I'm talking about..

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