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sprinkles08, Chrysler/Dodge/Jeep master tech
Category: Dodge
Satisfied Customers: 22813
Experience:  ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans and Hybrid Specialist
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2004 dodge ram 1500 slt: 4.7L V8 has 100,600 miles on it..surging

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my 2004 dodge ram 1500 slt, 4.7L V8 has 100,600 miles on it. I am experiencing a problem with the engine surging. I notice the Tach swinging wildly as much as 2000+ RPM's while going down the road. It runs at about 1600 rpm while on cruise at 55 mph and then I hear the engine revving and notice the tach swining up and down from 1600 to as much as 3500 rpm's and I feel the truck lurching a bit with the change in rpm's. It happens also when I am idling at a stoplight or even when the truck is in park an running. Had it checked out by a machanic and they changed the air filter, fuel filter and spark plugs, but the problem persists. any ideas?

Hello and welcome to JustAnswer!


I'm assuming the check engine light doesn't come on and there are no fault codes stored. If the light is on and/or there are codes stored then that would be the place to start to diagnose the problem.


It sounds like you've got a bad throttle position sensor (TPS). The TPS is mounted to the left side of the throttle body and tells the engine controller how far the throttle is open.


When the sensor gets worn it can start to create voltage spikes in it's signal. The engine controller will see these increases in signal voltage and think you are opening the throttle when you aren't. This causes the idle to increase and decrease on it's own.


The transmission controller also gets the TPS signal for shifting control. When the TCM sees these voltage increases while you are driving at a steady speed it will think you are accelerating and the torque converter clutch will unlock. This will give you an RPM increase of a few hundred RPM. In your case it sounds as if it's severe enough that the transmission is downshifting.

Customer: replied 6 years ago.
is the TPS the same thing as an Idler motor? My mechanic mentioned that as a possibility. This event takes place at both idling and at road speed. It happens when the vehicle is in park as well as when going down the road. If the problem is a TPS as you suggest, do you have any idea what expense I'm looking at for parts and labor? I would really like to hang on to this truck, it has been a very dependable vehicle up to this point with little to no repairs except for routine maintenance. I have had the transmission fluid and filter changed once at around 50K miles. Could this problem have anything to do with bad tranny fluid/filter too?

Ho, the TPS is different from the idle air control (IAC) motor. The IAC is mounted on the left side of the throttle body just under the TPS. It's job is to let air into the engine when the throttle is closed.


Replacing the TPS isn't major. The sensor will cost around $50 from your dealer, aftermarket will be less. Replacing it only involves unplugging it and removing two screws. It may be something you can do yourself, otherwise you shouldn't pay more than .5 to 1 hour of labor for a shop to do it.


The trans fluid is definitely due for change, but the fluid shouldn't be a factor in this problem.

sprinkles08 and 6 other Dodge Specialists are ready to help you
Customer: replied 6 years ago.
thanks for the advice. Sounds like the place to start looking.

You're welcome! Good luck with your truck and Happy New Year!



Edited by sprinkles08 on 1/1/2011 at 9:04 PM EST

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