I have an 02 Ram 1500 with 4.7l. It surges when at idle in gear or park, rpms rev up to about 1700 then down to about 600. It does this constantly at idle and seems to be worse when a/c is on. I have changed plugs andair filter. It is not showing any codes. Anyone have any ideas what may be causing this?

 

The problems sounds like thecomputer is working to keep the engine from dying. It revs high to keep it alive then eases off, but when it eases off the engine starts to die so it revs back up. Turning the AC on would add another component to help the engine die quicker so the after effect would be worse. Below is a few ideas of what can cause that:


It could possibly be the air intake. Get some throttle body cleaner and spray it directly into the air intake. Rig the throttle to hold between 2000-2500rpm then do short quick bursts around inside the throttle body with the cleaner.

Clean Mass Air Flow sensor... cleans it (VERY CARFULLY) with a q-tip and some warm water. Let it dry. Reinstall. Disconnect the battery for a minute to reset the computer..... Parts stores carry MAF cleaners as well.

Possibly replace MAF sensor.

Could also be a bad O2 sensor (this will be in the exhaust pipe shortly after the headers)

If it has been over 5,000 since oil change.... change oil...

Run injector cleaner through the system (usually a fuel additive)

Check fuel filter, if it is clogged it may not be supplying the system with enough fuel so the computer compensates up and down trying to keep the engine running.

Run a system self check. Steps: 1. hold in the trip reset button. 2. Turn key to ON position 3. Let system run test (WHILE still holding button in)4. Once done a code will be displayed, let go of the button and write down code. (Not sure if this will work on 02 or older)

IF all that fails to resolve the problem. Take it to a shop to be looked at. Most will give you an idea of the problem for free. (Dodge dealer I take mine to always checks it for free) If you want to pay them to fix you can. OR you can say you want to get a second opinion and either get one or do the repair yourself.

 

I could very well be wrong but...I was told a while ago here that the 4.7 does not have have a Mass airflow sensor. That being said I had a very similar problem with my '02 QC. I had left it in my driveway for a long while (8 mos) while deployed overseas and my wife was supposed to drive it once a week. That did not happen so when I got home I took it to the stealership and they had to replace all four of the fuel injectors on the passenger side of the engine. It seems they had corroded and were not spraying correctly. Not saying this is the case for you but something along those lines. Have you cleaned the TB yet? How about an injector service? You can buy a cheap kit at autozone. It hooks up to one of the brake vacuum lines (I know, weird right.) and the throttle body is as simple as disconnecting the resonator (black thing that says 4.7L Magnum) spraying the TB and wiping with a rag. Good luck and let us know how it turns out.

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Thanks, I will try cleaning the TB and maf and o2 sensor tonight and I will let you know how it goes.