Throttle Surge - JeepForum.com
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post #1 of 13 Old 09-20-2021, 02:45 AM Thread Starter
HampshireWJ
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Throttle Surge

Well this is an odd one and hopefully a one off.

Out wheeling and went through some muddy water, tide mark shows about 3" above bottom of doors, this is on a 3" lift, tide mark height due to uneven surface and one side of vehicle getting higher than the other. What happened next was very odd, out of the water with the car stopped and with foot on brake the RPM suddenly surged high and I could not stop the vehicle moving forward on the brakes. Came to an abrupt stop with the assistance of the back of a mate's Land Rover! This was on a 03 Overland and it was in 4 low at the time. Only damage was a broken number plate bolt.

No problems at all after this event for the rest of the trip.

Anyone had similar happen, knows a reason and any remedial action?

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post #2 of 13 Old 09-20-2021, 05:36 AM
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Either the throttle plate moved or the IAC did. Just an influx of fuel alone or air alone would not do that, it had to be both. If just fuel was added without air that would be pig rich and not jump forward. The same if just air was increased, no jump forward with power. I have had my IAC be slow letting idle to come down but have never had it take off after stopping, that would be the result of a signal from the TPS indicating to the PCM of throttle application. Even if the wiring was bad to the PCM from the TPS and showed the PCM the throttle was opening it could add fuel for that command however if the throttle plate does not open just fuel added will not result in unintended acceleration not to mention in that instance the PCM still would need inputs from other sensors such as cam pos, crank pos, MAP, etc.
Without pointing a finger could you have possibly been pushing the accel pedal instead of the brake? I ask because in the winter with big boots I have caught the accel pedal with the side of the boot going for the brake.
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post #3 of 13 Old 09-20-2021, 06:18 AM Thread Starter
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Thanks for that CDee.

I went through the same scenario, 'was it operator error'? - pretty convinced it wasn't, as it hit very high RPM very suddenly. I also tried a few times afterward pressing hard on the brake and using my heel to build the RPM and could not contrive a similar situation.
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post #4 of 13 Old 09-20-2021, 05:05 PM
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I'm curious if a scanner would show a code. Have you checked?

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post #5 of 13 Old 09-20-2021, 11:54 PM Thread Starter
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Good point WJ, will try that later today and report back.
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post #6 of 13 Old 09-21-2021, 12:43 AM
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Quote:
Originally Posted by HampshireWJ View Post
Well this is an odd one and hopefully a one off.

Out wheeling and went through some muddy water, tide mark shows about 3" above bottom of doors, this is on a 3" lift, tide mark height due to uneven surface and one side of vehicle getting higher than the other. What happened next was very odd, out of the water with the car stopped and with foot on brake the RPM suddenly surged high and I could not stop the vehicle moving forward on the brakes. Came to an abrupt stop with the assistance of the back of a mate's Land Rover! This was on a 03 Overland and it was in 4 low at the time. Only damage was a broken number plate bolt.

No problems at all after this event for the rest of the trip.


Anyone had similar happen, knows a reason and any remedial action?
I haven't a clue what caused it I'm afraid Hampy, but if it happened to me, I'd fit a kill button in case it happened again.
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post #7 of 13 Old 09-21-2021, 01:06 AM
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before a kill switch - or redesigning the vehicle MAYBE shift to N and if necessary turn key off.

Checking codes with a scanner is always my 1st step, yes anal, but 2nd I would ask what modifications other than lift?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 13 Old 09-21-2021, 06:34 AM
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Happens more often than one would imagine. It only happens to me with my big subzero boots on I wear while doing my snow removal work, I catch the accel pedal with the the front toe area of the boot. The way the floor is shaped doesn't help. You don't have a RHD by chance ?

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post #9 of 13 Old 09-21-2021, 07:27 AM Thread Starter
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CDee, yes it is right hand drive - was wearing normal pair of Doc Martens work boots, and when it took off the foot moved totally to the brake and the revs did not die down, so I am happy it wasn't operator error.

The problem happened so quickly with the RPM I did not have enough time to react to switching off the ignition nor put trans into neutral.

No codes recorded on the scanner. Following the incident I was putting the transmission into Park every time we stopped.
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post #10 of 13 Old 09-21-2021, 12:00 PM
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I think I just experienced what you mean. Leaving the store about an hour ago I put it in drive, hit the gas moving forward about 5 feet. Rear hatch was not closed so I hit the brakes and put it P but it caught at R from be not pushing it forward enough. It revved up to almost 1500 for a second then fell back down to idle in reverse really catching me off guard. Has never done that before, seems its to do with the PCM adjusting the idle speed depending on whether in gear or not. I did think immediately of this thread, if I was in 4 lo I absolutely would have tagged a car 10 feet in front of me.

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post #11 of 13 Old 09-21-2021, 01:02 PM Thread Starter
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Good to know I'm not alone!

Mate who I was out with confirmed that it was all the car not my errant foot. Apparently the revs dropped a little and then suddenly hit high RPM and was off.

My only thoughts are could it have been caused by the O2 sensors getting wet and sending odd readings? They would have got pretty wet going through the particular puddles.
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post #12 of 13 Old 09-22-2021, 11:25 AM
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Quote:
Originally Posted by HampshireWJ View Post
Good to know I'm not alone!

Mate who I was out with confirmed that it was all the car not my errant foot. Apparently the revs dropped a little and then suddenly hit high RPM and was off.

My only thoughts are could it have been caused by the O2 sensors getting wet and sending odd readings? They would have got pretty wet going through the particular puddles.
I think I would prefer it if you were alone Hampy.
2 instances in a few days of each other is worrying.
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post #13 of 13 Old 09-25-2021, 11:47 AM
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This has also happen to me with big shoes I don't normally ware.
It has also happened as a result of an erratic TPS. A bad TPS can cause erratic idle. If the TPS (or any other sensor) allows the idle to drop too low the computer will catch it and increase the idle to keep the engine from dying. (sometimes too much).
A bad TPS can also allow the idle to drop so low that the engine dies.
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