2006 GT Jumping forward after startup? - Mustang Evolution

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Old 06-20-2012, 01:20 AM   #1
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2006 GT Jumping forward after startup?

Hey guys. Today when I got off work, I started my mustang, kicked it into drive, and it started lunging forward without even touching the gas. The RPM's would go from 750-1k and the car would jump about a foot forward...

Is this because the engine is cold? Or is there something wrong?

It's a 2006 GT, auto, 90k miles. Thanks guys.

I put the car into park, let it sit for a few minutes, then back to drive and it was fine.
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Old 06-21-2012, 08:36 AM   #2
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Re: 2006 GT Jumping forward after startup?

In my experience, all auto cars have a slightly higher idle when cold. My Manual does this. It starts high then for the first few seconds it idles normally after slowly coming down.
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Old 06-21-2012, 10:03 PM   #3
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Are your rpms normal? It really shouldn't lurch like you're describing.

All cars idle high at start (auto or stick is irrelevant); it's part of the open-loop and closed-loop engine operation.

When the engine is first started, the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal.

The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature - about 40C/104F usually
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.
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Old 06-22-2012, 12:18 AM   #4
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Re: 2006 GT Jumping forward after startup?

^ Thanks! That was a super interesting read.

My RPMs are completely normal. It's only done this one other time in the past, and it's when it was roughly 30 degrees outside. It seems to have to do with the cold, honestly.
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Old 06-22-2012, 07:19 AM   #5
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Re: 2006 GT Jumping forward after startup?

Quote:
Originally Posted by BackPressure View Post
Are your rpms normal? It really shouldn't lurch like you're describing.

All cars idle high at start (auto or stick is irrelevant); it's part of the open-loop and closed-loop engine operation.

When the engine is first started, the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal.

The system will stay in 'Open Loop' until the following conditions are met:

1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature - about 40C/104F usually
3. A specific amount of time has elapsed after starting the engine.

The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.
Correct but that lunge forward on a stick isn't really there because you just don't pop it in drive. Only reason I said omitted manuals from it

I have never owned an auto car that DIDN'T lunge forward to about 2 MPH just by popping it in drive when cold.
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Old 06-22-2012, 02:52 PM   #6
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Quote:
...I have never owned an auto car that DIDN'T lunge forward to about 2 MPH just by popping it in drive when cold.
Exactly! Especially a high-torque engine at startup.
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Old 06-22-2012, 07:27 PM   #7
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Well normally I put my foot on the brake when going into drive so that doesn't happen.
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Old 06-22-2012, 11:53 PM   #8
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Give her a minute or two to warm up, if the problem persists then come on back and tap our collective motor-knowledge to help.

Also: is it a BIG lurch, or just a 2-5 mph lurch?

WAIT A SECOND! You mentioned putting your foot on the brake whilst changing gears. You do that normally, correct? You don't just brake to get out of park and pop into drive I hope.
(seriously no offense here, just a honest question for clarity)
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