2014 Equinox 2.4 low idle bucking on load - TerrainForum.net: GMC Terrain Forum
 
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post #1 of 3 (permalink) Old 01-25-2020, 06:21 PM Thread Starter
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2014 Equinox 2.4 low idle bucking on load

I can't seem to figure out what the issue is with this car, it seems to buck a little at low rpm up a hill as if the transmission isn't downshifting. The only code on the scanner was a P0120 for TPS and it wasn't a hard code. I did witness it last week with a fluctuating idle when in park after driving, but never happened again.

Today I drove it around and watched the scanner data and could see the erratic TPS data, accelerator pedal sensor data was fine. So with the code getting triggered at some point and seeing the erratic data, I decided to replace the throttle body/TPS sensor. Got an AC Delco for a good price. I feel more power now and attribute that to a dirty throttle body and having a new one now, but the slight "bucking" is still there. If I depress the accelerator harder it downshifts and goes away.

Had the transmission rebuilt last year, has about 160k on it now and the tranny has about 30k. No codes and haven't really drove it too much with the new throttle body, but without any codes, I really don't know where to look. My gut tells me I have a torque converter or transmission control module issue. The tranny is under warranty until July but without something concrete they'll defer the issue to something else. I may have to take it to the dealer for more in depth diagnostics. Can't really say its programming because it was fine until 2 weeks ago. Any idea what other data to look at? I'm running an Autel so I have access to view live data.
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post #2 of 3 (permalink) Old 01-26-2020, 09:39 AM
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Test drive using manual mode and see if it's still doing it. That can help to see if it's trans. or engine related. Spark plugs fresh and AC ones ?

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post #3 of 3 (permalink) Old 02-06-2020, 01:05 PM
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Is it ?? ..... the engine "stumbles" ?

Engine oil pressure is used by solenoids
to activate the variable valve timing
of valves opening and closing on the combustion chamber.

It could be the solenoid
that controls the VVT variable valve timing, has filter screens ( on the solenoid)
that are plugged with engine oil gunk.
When you step on it, and vvt solenoids are electrically energized,
The engine oil, and subsequent oil pressure,
is SLOW in flowing thru the plugged screen cloth on solenoid
And engine oil pressure is not able to activate the solenoid, the solenoid which advances engine timing,
fast enough..... hence a stumble.

There is a recent post on traverse forum, called
"Traverse Stumbles on light acceleration No Codes"
where a brilliant "testbob" disassembled
Then cleaned the filter screens on the 2 solenoids....
( one solenoid controls the intake valves, the other solenoids controls the exhaust valves)
He actually has 2 separate posts on the same topic, look for them, read his comment and his solution,
he fixed his problem.
Here is One post
https://www.traverseforum.com/thread...o-codes.19479/
His 2nd post is a detailed summary of his findings.



Is That ^^ root cause.... WHO KNOWS??

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