Throttle body won't throttle down - GMC Acadia Forum: AcadiaForum.net
 
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post #1 of 3 (permalink) Old 05-17-2017, 10:17 AM Thread Starter
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Throttle body won't throttle down

I have searched and read several posts about the throttle body and code P1516 along with idle speed issues, but my symptoms are a little different so I'm hesitant to replace the TB.

Was in stop/go traffic for 10+ minutes and suddenly got service stabilitrac/traction control disabled/engine power reduced messages and the CEL came on. Was able to limp to the destination in the slow traffic and parked for about 2 hours. When restarted for trip home the CEL was on but no other messages and car drove fine.

Got home and pulled code P1516, and recommendations here and elsewhere were to clean TB and also remove any oil in the air tube, which I did. The oil was not "milky" like some have reported, but the TB was pretty dirty so I removed it to thoroughly clean. I did not replace gasket.

I cleared the code and have not had any CEL or messages pop up, and the car idles perfectly fine at a standstill. However, the issue I have is after applying throttle, either briefly or sustained while cruising, the throttle does not seem to fully throttle down when coming fully off the accelerator pedal. In other words, if I take my foot off the gas to coast, the car will easily maintain speed on a flat surface or even accelerate slightly if in a lower gear, and when I apply the brake to decelerate to a stop it takes more than usual brake pressure and the rpms are staying around 1300-1800 while the trans downshifts. The downshifts are also very noticeable especially in the lower gears, and it is not until I get below about 5mph that the throttle seems to fully reduce to where it should for idle. Like I said, it will then idle normally once at a standstill, whether in gear or P/N.

If this wasn't a drive-by-wire throttle system, I would describe it as if the throttle plate or cable was sticking, but I know that's not the case, and the issue consistently corrects itself upon coming to a near stop <5mph.

I tried the "learn procedure" here with no improvement: http://www.acadiaforum.net/24-engine-drivetrain/12968-throttle-body-replacement-reprogramming.html

Anything else I should try before I drop $100+ on a new TB and gasket?
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post #2 of 3 (permalink) Old 05-17-2017, 06:19 PM
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I'm wondering if it could be an "adaptive driving" thing that will go away once the car is driven for a while.

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post #3 of 3 (permalink) Old 05-18-2017, 09:51 AM
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I would wait and see if it corrects itself.

While chasing a hesitation problem on my 2012 I replaced the TB and the problem went away for a couple of weeks. It idled a little high, seemed to keep the engine speed up with later shifts and earlier downshifts. Eventually it went back to normal, and my hesitation problem returned.

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