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Thread: Strange idle, bad mileage help!!
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02-05-2008, 04:32 PM #1
Strange idle, bad mileage help!!
I have an 02 Z28 with 30k miles on it, lately it has been idling anywhere between 1000-3000 rpms and getting about 13 mpg. It is a six speed so the millage is way off. It does have an air box, flowmaster, and 4:11 gears. I just replaced the O2 sensors and it has changed nothing. I dont know much history on the car so it could have a tune in it or anything, but the dealer wants $80 to flash the ECM. I dont want to do that unless I am pretty sure it is the problem. Also no check engine codes, could be the MAF sensor. Any advice would be appreciated.
Thanks,
Dave
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02-05-2008, 07:55 PM #2
sure sounds like a vacuum leak after the TB...
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02-05-2008, 07:59 PM #3
well i had the problem with weird idling but not at those rpms...anyways i got the MAF changed and my car runs perfect!
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02-05-2008, 10:15 PM #4
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02-05-2008, 10:35 PM #5
yup, I'd check the pcv hose going to the intake first. Those have a history of either cracking or having a hole get rubbed in the backside of them.
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02-06-2008, 07:36 PM #6
Checked the vacum leak with no success, getting the ecm re programmed by gm on friday. I unplugged all the emmission controls and never had a change idle or a code pop up, so something tells me the car has been tuned.
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02-07-2008, 06:08 AM #7
I bet money you are wasting your time blaming the PCM.
Why not look towards the most common and obvious of things; those devices and bits which are mechanical and/or exposed. I suppose an IAC coil driver could fail but it is unlikely and it will set a code right away. Some cars take a while to set codes after emissions items have been removed, so to say it has been tuned based on that is a bit of a stretch.
Do a search and find out how many bolt-ons guys have problems and how many of them blame the PCM... then look at how many say the PCM actually fixed their issue. Just saying...
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02-07-2008, 07:01 AM #8
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02-07-2008, 07:08 AM #9
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have you checked your MAF sensors??? i know people who do the K&N recharge kit the wrong way and end up getting the recharge oil all over the sensors and it has the same symptoms that you have desribed...
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02-08-2008, 10:31 AM #10
$45 to get the pcm flashed, ill let you know how it turns out, going today
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02-08-2008, 11:16 AM #11
please do. These threads always help other people down the road somewhere.
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02-08-2008, 11:48 AM #12
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02-08-2008, 07:04 PM #13
Well after getting the ecm reprogrammed the idle is back to normal and seems to running great, as far as the millage I will have to see how many miles I get out of this tank, hopefully it will be anywhere from 250-300 miles will let ya know
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02-08-2008, 09:36 PM #14
Doesn't make much sense... If something were "bad" inside the PCM (minus a physical output driver or bad input) as far as programming, it would fail checksum test and the car wouldn't run.
Regardless, glad to hear it's better
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02-09-2008, 01:58 AM #15
yep, glad to hear it's better. I'd wonder what happens as it learns the trims again. How many miles have you put on it since the reflash?
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02-09-2008, 05:38 AM #16
Only about 100, but the guy I got the car from had a cam and stuff in it, so im thinking he used an ls1 edit and then removed the cam and left the tune in.
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02-09-2008, 05:59 AM #17
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