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Recently purchased an 07 Chevy Colorado with 2.9L 4-cylinder engine and automatic transmission from used car dealership. Had an independent shop do a complete pre-purchase inspection and they didn’t find anything major wrong with it.
Over the last two weeks I’ve had it, I’ve done lots of driving, including a 500-600 mile trip from Fairfax, CA to Reno, NV and back. Throughout all this it has performed wonderfully, except I seem to have a crappy idle now. It idles a little bit rough, and when I’m coming to a stop with the AC on the RPM fluctuations from around 500 to what it usually idles at around 800. At the beginning it didn’t do it, and now over the time I’ve owned it it seems to have gotten worse.
Of course, when I hooked up my Scantool yesterday I was unable to replicate the problem as much. I will attach some pictures of my scantool readings – I do find the 99% fuel trim a bit odd – or is this normal?
I’ve done my research on this problem and a common issue is build up on the throttle body causing this. I’d like to attempt to clean the TB but I’m not really a mechanic. It looks easy enough but I’m afraid to do it in case I mess something up. I can’t afford a costly part or repair right now.
Here is a link to a tutorial I found.
http://coloradofans.com/forums/67-technical-questions-tips-how/117780-how-tb-throttle-body-cleaning-pics-updated.htmlAnd more information that leads me to think this really will fix my truck. The OP in this thread had the exact same issue and the same concern/hesitate I had about doing it:
http://coloradofans.com/forums/77-care-cleaning-detailing-maintenance/148657-cleaning-throttle-body.htmlDo you think that I should give this a shot? Can I just remove the intake tube and visually inspect the throttle body to see if there is build up on it?
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see if this helps.
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
Be very careful cleaning the throttle body. Just do a quick search of this forum and you’ll probably find over 100 posts where people cleaned their throttle body only to have issues afterward. That said, if it’s only happening with the AC on, I suppose it’s also possible that there’s a problem with the AC. Based on your description of where you live, I suspect the AC gets used quite often. Perhaps there’s something happening there. Given that you’re not a professional, you might have the AC checked out as well to see if that’s the cause of the idle problem.
Good luck and keep us posted.
[quote=”mstk415″ post=141295]I do find the 99% fuel trim a bit odd – or is this normal?[/quote]
It is normal when using a non-manufacturer-specific scan tool with generic PIDs. What is happening is that there is no sensor that matches that PID installed on your vehicle. The software is then extrapolating that value for the non-existent sensor by subtracting the sensor that you do have from 100%. If you add the two short-term fuel trim values they will add up to 100%. As the sensor you do have varies, the other will as well, to maintain 100% between them, depending on how often the computer refreshes the calculated rate. In other words, just ignore the value for STFT bank 1 sensor 2, you don’t have one.You may find it helpful to clean the MAF sensor. In fact, I would do that before attempting to mess with the TB. Many times its just a dirty MAF that can cause idle issues. A dirty idle air control valve (IACV) can cause idle issues also. Only suspect the throttle as a diagnosis by elimination. As Eric said, a lot of folks have issues following a throttle cleaning, especially with electronic TBs (DBW, ETC, or TAC). You can inspect the throttle plate and bore, if it not really nasty, it may be best to leave it alone. If you really do feel that it is dirty enough to clean, just spray a few short bursts of TB cleaner around the plate and walls, and a soft rag to gently wipe off the excess deposits. No need to remove the TB, or drench it in cleaner. Have a helper sit inside with the key on and hold the pedal to wide-open while you wipe out the TB. Do not manually operate an electronic TB, it can damage the motor and/or position sensor.
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