2002 1500 4.7l 4WD 160,000 miles.
Recently the truck has developed an RPM fluctuation. Symptoms are:

1. At highway speeds on relatively level surface (i.e. not down shifted) RPMs modulate about 200-400 every 15-20 seconds. Happens with cruise on or off.
2. At idle flucturates about the same RPM range - 200-400.
3. On start up the engine revs higher than it used to before settling back to idle. Sometimes as highs as 1500-2000 RPM.
4. Not frequently but sometimes on a coasting upshift the transmission will hang engaged a bit too long the hard upshift.
5. From startup until normal operating temp, the engine will ping under acceleration.

No stalling, no check engine light, haven't checked for codes.

Other threads seem to point to the throttle position sensor as likely culprit but I haven't seen mention of 3, 4, or 5 associated with a TPS. Comments?

Thanks for your help. This is a great forum and has saved me $$$ many times.

 

Check your plugs and wires, sounds like an cylinder ignition issue to me. Basically what is happening is a cylinder is failing to fire, and the engine kicks up the RPMs to compensate for the lost power, and then it comes back. An intermittent problem like that is either fouled or worn out plugs, or arcing wires.

 

PYRO learned that lesson the hard way

 

What lesson? His truck is doing the same thing mine did when it wanted new plugs.

 

I would check plugs, coil packs and TPS. 4.7s don't have the traditional plug wires like the Hemi's. Factory maintenance interval is 30k mi I believe. Also a lot of parts stores will perform a free OBDII scan, however, if the CEL isn't illuminated then it may not be throwing a code. I think I read somewhere that the 4.7s didn't have knock sensors 'til 2005 (could be wrong on that though). After removing the TPS I think you have to reset the PCM also and while you're there a good throttle body cleaning couldn't hurt. just my opinion. good luck.

 

Thanks. Forgot to suspect the simple things first. I''ll post the results when I get the plugs switched..

Can those coils be ohm'd like a regular coil? If so, what's considered passing?

 

The check engine light came on today so I expedited changing the plugs. Not a hard job, just a PITA job. Seems to have cured all the problems, the truck is running fine. The gaps were maybe double what they should be. I think I missed changing the plugs out last time around. I replaced them with Autolites. The old ones were Champs.

Of course there was that other thing...

Oil in the #4 spark plug well. I got an oil bath when I blew compressed air down the well before removing the plug. Any ideas? I think I'll start a new thread..

 

you learned the lesson that ignition can do that. you learned it the hard way cuz you had to ask hammer

 

My 2002 ram with 4.7 had the same problems with rapid idle at start up mine went as high as 3000 rpm and would only come down after full throttle rev. I ended up talking to a mechanic friend he said that your curb idle should be just about 600 w/o ac running. Told me to try tps sensor being a relative cheap repair and that there were no codes coming up on the computer. Since changing tps sensor all idle problems and drivability problems went away. Best $50 buck spent

 

I have been at this for a couple of years now and I still have not isolated the true cause of my trucks issues.


Symptoms:
1) Sometimes the engine revs higher than normal on start up.
2) Sometimes at idle, either parked or in gear, the engine will repeatedly
rev from idle, approximately 650 rpms to about 1500 rpms.
3) Most notably while on cruise control, the rpms will repeatedly surge a
couple of hundred rpms. It has done this with cruise control off but it
is very rare.
4) No codes.


Quick fix: From idle, over revving the engine seems to solve the issue for a day or so. While cruising, stomp the gas and get the rpms up as high as safe.
This also clears the issue temporarily.


Work I have done on the engine:
1) Replaced coils and plugs.
2) Replaced Throttle Position Sensor.
3) Replaced Idle Air Controller
3) Replaced Manifold Absolute Pressure Sensor
4) Replaced the PCV valve.
5) Installed catch can on PCV hose


With regards to the MAP: I discovered oil on the MAP sensor and began looking at blow by as the cause of the MAP sensor not functioning properly.
Once I did get a code related to the MAP sensor. Cleaning it and or replacing it fixes the issue temporarily.


Looking to reduce the oil being drawn into the intake manifold I replaced the PCV valve. Replacing the PCV valve did not solve the issue. So, I added a catch can to the PCV line running from the PCV valve to the intake manifold. It does catch oil, thereby, in my opinion reducing the oil drawn into the intake.


Another symptom: the first plug on the passenger side. The plug closest to the radiator. The plug nearest the oil fill point. Is red. The insulator around the electrode is red. None of the other plugs are that color. Also, the pressure of that cylinder is much higher than the pressure of the other 7 cylinders. I am assuming that excessive oil is either being deposited in that cylinder from the intake or it is being drawn up from the crank case, which again is why there may be an excessive amount of oil being drawn into the intake, causing the MAP sensor to toss a code, and or cause the engine idle to change the way it does.


BUT!!!!! None of my repairs has stopped the issue. The thing that gets me is revving the engine solves the issue temporarily. But I am out of ideas as to what could be becoming clogged/fowled and be slightly cleaned by revving the engine. The truck runs fine and tows fine. The cruise control issue annoys me when it happens as does the idle revving. But other wise I would say the truck runs fine.


Well, it's been a couple of months now and doesn't look like anyone has any new ideas. I took the truck to Dodge though. They had no new ideas either. Checked the compression and looked over everything, all seems fine. I still occasionally get the surging at idle. But it runs much better than it did before installing the catch can on the pcv line. I've not had any luck finding a better catch can than the air water separator I found at Harbor Freight. I'm planning to make myself a larger catch can with pvc fittings and hang it on the breather box. Hope this helps someone else. Consider it closed.