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Discussion Starter #1
My '10 Z71 was having a weak/rough starting issue, so I did some googling. I have recently replaced the plugs and wires, battery was about two years old, so I decided to try the advice to clean out the throttle body. It did have some build-up over 160k miles.

When my son was holding the gas pedal down (car off) so I could clean out the tb, he said the low battery warning came on. It was only a couple minutes.

Checked the battery, and it was at 11.xx volts. Bad. And the source of the rough starting.

So I changed out the battery, and now, of course, since I cleaned out the tb, the calibration is off. It will idle fine when started. Tried the idle 3 min, off 1 min, idle 3 min procedure, and I also did the accel/decellerate over 44 mph routine, but letting off the gas does not close the butterfly in the tb. Coming to a stop, I can feel the engine still trying to move the truck forward, and the downshifts are pronounced (as you'd expect). In park, if I rev up the engine, it will either return to idle very slowly--like 35-55 seconds--or it seems to hang at that rpm until I shut the damn thing off. I did get a PO507 idle code. Cleared it an it hasn't come back just yet.

I've driven it about 60 miles hoping it will relearn, but not much improvement. Do I just need to log some more miles, or will I need to bring it into a shop with a real scan tool that can to a tb adaptation directly in the ECM?
 

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Discussion Starter #3
Well, battery was disconnected, since I had to change it. I could try that again, but wouldn’t that be starting from 0 if the ecu is relearning the tb positions?
 

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Well, it returns to factory specs

None of which are high idle and a butterfly that doesn't close.

You need to reset the throttle body, don't worry about the PCM "learning" your habits
 

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Discussion Starter #5
I verified (with the motor off) that the butterfly in the tb is opening and snapping shut as the gas pedal is depressed and released.
I have no idea how the engine can continue to rev with my foot off the gas, unless the ecu is holding the butterfly open?
 

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In a Drive By Wire system, the butterfly (Throttle Plate) is moved by the Throttle Position Sensor, the TPS (mounted on the Throttle Body) monitors the position of the gas pedal using the Accelerator Position Sensors.
At this point the PCM is not involved.
When the APS tells the TPS that the pedal has moved, the TPS actuator follows the movement opening the TP.
The movement of the actuator causes fingers (wipers) to move over a resistance (just like an old fashion radio volume potentiometer). The resistive change is passed to the PCM as input, so the PCM knows the pedal is being moved. The PCM knows from the resistance value where the butterfly is and therefore what the air intake should be.
And, air intake change is what causes the engine rpm to change.

You did follow proper procedures by having someone hold the pedal down while you tried to clean the TB, however, just the slightest movement by either of you and the butterfly has been bumped out of sync.

You need to reset this mis-alignment.
The correct way is with a scan tool; but a battery disconnect may do it if you are lucky.
 

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Discussion Starter #7
Ok I’ll try another battery disconnect.
But the battery was disconnected for 40-60 minutes after I cleaned the tb and buttoned all that up and before I have been experiencing theses symptoms.
 

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Zak, like you, I don't expect a battery disconnect will fix it; but it is a cheap try.
The other option is to go to a dealer and have it reset, which will cost you an hour at dealer rate.

Now, don't take this the wrong way, but in the time we have been talking about this, you could have tried the disconnect and reported back.
 

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Discussion Starter #9
Battery disconnect (for 10+ minutes with headlight switch on) cleared the P0507 code but did not change the tb behavior.
guess I should give the dealer a call on Monday.
 

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Discussion Starter #11
Actually, I decided to redo the 3min idle, 1 min off, 3 min idle procedure again. This time I waited over a minute to restart it. Took it for a drive.
Symptoms seemed better, but not fully cured. Still felt a push coming to a stop, but the downshifts weren’t as noticeable. When I parked it in the driveway, I revved it and the rpms didn’t hang when I let off the throttle. They still took a good time to drop, but before they would stay as if I was still pressing on the gas.
Going to take it for a decent drive today and do the accel/deccel over 44 mph procedure.
I hope that will do it.
 

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Discussion Starter #13
Got an appointment for 8:45 Wednesday morning at the local dealer (DeNooyer here in Albany). I'm afraid for me credit card. But these power downshifts can't be good for my tranny (which I just had to have rebuilt).
 

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Discussion Starter #14
So, the dealer (DePaula, not DeNooyer) did the tb adaptation ($135 plus tax) and it drives fine again. Ecu had a Compensation of 49%, reset it to 10%.
 

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I know it’s like a three hour drive but worth the trip to South Main Auto in Avoca. Eric fixes the cars the dealers can’t fix.
 
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