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Have you checked the PCV? A clog in that can increase crankcase pressure and reduce fuel efficiency.
Yes - the PCV is functioning normally and I replaced and drilled out my PCV valve on the back VC last summer. I've also replaced the o-rings on the PCV tube that connects to the top of the intake and the PCV valve.
 

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Okay guys, quick update, you're going to think I'm crazy but it looks like the culprit was the MAF sensor. I noticed today (before replacing the MAF) that when driving around the motor was idling higher than normal and was steady around 800 instead of the 600 stock idle. I didn't think anything of it really (other than I thought it was higher than normal) until I replaced the MAF as right off the bat it started idling smooth at 600 on the button without fluctuation and always returns there while stopped and also idling like at a light or in a parking lot. I also was able to drive about 30 miles(ish) and noticed the MPG's climbing rather rapidly on the DIC (just reset it yesterday at fill up). Time will tell if the MPG's go up over all and I'll see how it responds this week. Also, I noticed the shifting seems a bit smoother and it seems to shift at lower RPMs. I never had any MAF codes and the car actually didn't run poorly, but I'm shocked so far that the MAF seems to be the issue and maybe just getting weak or old (125K)? Also, YES - I did clean the MAF with proper MAF cleaner and let it dry a few hundred miles ago with no change.
 
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Glad to hear you got resolution! Sometimes sensors go bad and cleaning doesn't fix them, so I don't think you are crazy at all.
 
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very interesting. So it was always idling high- and taking longer to shift-- so holding RPMs higher.
 

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very interesting. So it was always idling high- and taking longer to shift-- so holding RPMs higher.
Not sure when the idling a bit higher started as I honestly haven't paid much attention, but I definitely noticed the MPG's drop as I reset the DIC at every fill-up to keep track of it. My presumption is the shifting was also affected a bit and shifting a bit higher as well. It's still working and idling great with the new MAF and the MPG's are still climbing. Guess MAF's can get lazy without throwing a code just as O2's can as well, just strange to me.
 

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Not sure when the idling a bit higher started as I honestly haven't paid much attention, but I definitely noticed the MPG's drop as I reset the DIC at every fill-up to keep track of it. My presumption is the shifting was also affected a bit and shifting a bit higher as well. It's still working and idling great with the new MAF and the MPG's are still climbing. Guess MAF's can get lazy without throwing a code just as O2's can as well, just strange to me.
Of note, high idling (up to 800 or so based on my scangauge) is not necessarily an indication something is wrong. Along with other symptoms, as your experience shows, this can be a symptom of a larger issue. I'm mostly posting this in case others find this thread and just trying to help educate them.

If the battery is low, like when I sit for lunch with the engine off and the radio on, the alternator needs to be spun faster to charge the battery so the idle speed both in park and in drive is higher. Same with if the A/C is running full blast and the cooling fans are running at their higher level, the load on the alternator is higher so the ECM kicks the idle speed up to keep the battery charged.
 

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Of note, high idling (up to 800 or so based on my scangauge) is not necessarily an indication something is wrong. Along with other symptoms, as your experience shows, this can be a symptom of a larger issue. I'm mostly posting this in case others find this thread and just trying to help educate them.

If the battery is low, like when I sit for lunch with the engine off and the radio on, the alternator needs to be spun faster to charge the battery so the idle speed both in park and in drive is higher. Same with if the A/C is running full blast and the cooling fans are running at their higher level, the load on the alternator is higher so the ECM kicks the idle speed up to keep the battery charged.
True, but in my case, the instantaneous change in idle, shifting patterns and MPG, immediately after changing out the MAF seems pretty conclusive. Time will tell, but I'm pretty surprised myself as well.
 
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MAF also measures intake air temp. as well as air flow. In the '80's they used to use a speed/density mapping system before going to the MAF / intake air temp method. Had a Z24 Cavalier with the speed density setup.
 

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MAF also measures intake air temp. as well as air flow. In the '80's they used to use a speed/density mapping system before going to the MAF / intake air temp method. Had a Z24 Cavalier with the speed density setup.
Yup - my 13' BMW X5M - is SD tuned as well as it doesn't use MAF's with the twin turbo setup. I didn't know our 3.6 used a IAT from the MAF as I'm used to separate IAT sensors as with my 95' TransAm.
 
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