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