P0171 and the Dreaded High Idle After TB Cleanign - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 4 (permalink) Old 02-09-2017, 11:43 PM Thread Starter
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P0171 and the Dreaded High Idle After TB Cleanign

2010 LT autotragic with about 110,000 miles under her.

I have had P0171 pop on and off for the past 21/2 years of owning this magnificent turd, but I felt I needed to mention the code as well.

So backstory. Had a buddy who services all my cars do an oil change and TB cleaning. He hosed the TB down with TB cleaner like it was a protester in the streets, then poked a soft microfiber cloth in and out to get the crap out of the hole.

Yes, he moved the butterfly valve manually with one finger. Engine was off, Battery was still hooked up.

After putting all the hoses and intake back on, it took a bit of coaxing for the engine to stay idling by itself. Now when it did, it ran fine and actually alot smoother now the TB doesn't have, well, TB. Now here comes my dumb self in the driver seat about 5 minutes of the car idling. I get out of the car and hit the accelerator with my big toe while stepping out. The car screams to 3,000 RPM and refuses to come back down. We turn it off, check for vacuum leaks and the sort, nothing is found. After coaxing the pos back to life again the idle stays nominal, 800rpm or so. Put it in gear, let off the brake, the idle will jump to around 1200rpm and the car will "accelerate" up to a coasting speed of 20, where the idle thinks it's okay to be.

After a week of doing drive cycles both city and freeway driving, the car is a bit better, the idle doesn't always go to 3,000rpm, but now to a more less butt clenching 2,000. I also have this awesome little problem in which I am accelerating and the car will lose power from 2,000-2,400rpm. It doesn't always do it but it feels more like a twitch if that makes sense. We have tried the relearn procedure, unhooking the battery, and a completely different intake. I am at my wits end and now thanks to the extra strain on the brakes, I got those to do again, which were replaced 3 months ago.

I do not have access to a gm scan tool, and I am really hoping to not buy a new TB as even the local scum junkyards want $150 for one. Any and all information will help. I know this is thread #40,931 about this issue, but it seems someone else has it slightly different and their fix isn't working.
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post #2 of 4 (permalink) Old 02-10-2017, 04:34 AM
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You can find a used TB online for a lot less. Hell, I might even still have my old one - I don't recall if I sold it or not. Though, I'm not sure if the LAP has the LE5's TB or not, considering it has the same intake manifold.

1986 Chevrolet Camaro IROC-Z - Wrecked/Sold
1998 Chevrolet Cavalier - Wrecked/Donated
2007 Chevrolet Cobalt LT - M62 Supercharger, Ported Throttle Body, 42 lb/hr Injectors, Intense 2.9" Pulley, Cobra Heat Exchanger, SS/TC Exhaust, TTR Engine and Trans Mounts, Trifecta Tune, ZZP Header and Downpipe, '08+ FE5 Struts/Shocks, SSC Springs, FE5 Control Arms, SS/SC Front Swaybar, Powell Hardcore Rear Swaybar, 18" MSR 045s, Dunlop ZIIs, Nightshaded Tails/Side Markers, Shorty Antenna, Black Bowties, Black Grilles, Black Headlights, Dual JL 12" w1v2 Subs, A/D/S Front/Rear Speakers, Pioneer 7" Touchscreen, G85 Recaros, Leather Rear Seats, 160 MPH Cluster.
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post #3 of 4 (permalink) Old 02-10-2017, 12:09 PM
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Thatgmpartsguy.com will have the throttle body. If you end going that route, but without knowing what CEL you are currently showing its hard to now for sure. G to a parts store and get it scanned, and post the results. More help can be given then. Also if you haven't already, try disconnecting the battery for a while, and see it that helps any. I swapped a maf sensor and it caused an idle problem for a little bit. I disconnected the battery and ECU. When I connected it and started it went away.

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post #4 of 4 (permalink) Old 02-10-2017, 02:12 PM Thread Starter
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Current and only cel is P0171. I had it cleared when I got new struts put on. 130 bucks installed with warranty, not bad. I had it cleared and the shop did the throttle relearn and it's tons better. However, it will go to 1500 rpm and be a slight pain with the idle hanging. Thought it's 90% back to normal. If it doesn't settle down by next Friday I'll look into a new tb
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