Surging idle at cruising speed

summerstang95

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I have a 95 Mustang 5.0 auto with 31k all stock. After about a half hour of driving the car will surge between 500 to 1500 up in rpms. It only does it for about a second or two. Speed of the car stays the same. It does it when the O/D is off or on. Only does it when driving at a steady speed between 35 to 60 and after approximately a half hour of driving. It did it about three times on an hour drive during the day and on the way back, at night, didn't do it at all.
I have gone through thousands of post.
I have change the EGR, TPS, cleaned the ACI, did a smoke test, reset computer, new fuel pump, new fuel filter.
The car idles great, drives great, lots of power, just has this issue when driving at cruising speed.
I'm starting to think the transmission is going. It might be getting too warm and then does the surging. Could the transmission oil be bad? Is there a sensor on the transmission that could be bad? The shop I took it to had no idea why it's surging.
Any help would be appreciated.
 

07GtS197

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Check the level with the car warmed up in park on a level surface.

If that isnt the issue my money world be on the mlps (manual lever position sensor) or transmission range sensor. Its a common issue on aode’s and early 4r70w’s. The sensor itself isnt too problematic but they are prone to water intrusion into the harness.


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ttocs

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I recently had a similar problem when the motor was up to temp. It was the TPS that was showing 2-5% when I was not giving it any gas. It was pretty easy to diagnose by tapping on the tps when it was hot. After swapping the tps it still did the same thing, turns out it was the harness going to it.
 
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summerstang95

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I recently had a similar problem when the motor was up to temp. It was the TPS that was showing 2-5% when I was not giving it any gas. It was pretty easy to diagnose by tapping on the tps when it was hot. After swapping the tps it still did the same thing, turns out it was the harness going to it.

Did you have to replace the entire harness or just the wire leading up to the TPS? They don't make a harness for it anymore. Would have to buy a used one or have one custom made.
 
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summerstang95

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So I tested the new TPS and I get 0.564 which is low, should be .98. Increases to 3.21 with full throttle. Did I get a bad "new" TPS or am I missing something?
 

ttocs

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So I tested the new TPS and I get 0.564 which is low, should be .98. Increases to 3.21 with full throttle. Did I get a bad "new" TPS or am I missing something?
I just picked up a tps harness from I think it was autozone a little more then a month ago. It wasn't something they had on the shelf that night but they got it in the next day.

It sounds like something is bad in there somewhere but its hard to say. STart testing it again for voltage and then slowly slide the throttle blade till its completely open. It should have a nice smooth sweep like you said from .98 to 3.2 but if you find a spot that shows no voltage/open, then the tps is bad for sure.
 
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summerstang95

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Update to this thread. Replaced the MLPS, manual lever position sensor. Seems to have solved the problem. Couple hundred miles and no surging anymore.
 

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