02 Ram 1500 4.7 stalling/surging at idle

Just yesterday, my truck began misbehaving. When stopped at intersections, the engine oil pressure guage would begin to fluctuate..dropping down then back causing the check guages light to come on.
Today, its not doing that anymore but when stopped at an intersection etc, the rpms would flucuate between 900 and less than 300 ( would stall if I left it in gear, put it in neutral and remove the load on the engine and the rpms would not swing low enough to stall out the engine). Also if left in gear it would surge as well, like the computer is trying to correct some issue and is over correcting.

There is no check engine light yet, haven't hooked up a scanner to look for pending codes yet.

Last year had the same issue with the engine oil pressure, I changed the oil pressure switch (oil pressure was good) and that took care of that issue. Hard to believe it would be the switch again..wonder if there is some loose wire somewhere or corroded contacts etc...trouble is, where to start when it comes to wiring and electrical..:confused:

Update: I used throttle body cleaner and thoroughly sprayed the throttle plate, and removed the IAC and cleaned it up as well with the spray, also checked the PCV valve since it was right there...it had a bit of sludge on it but nothing major, cleaned it up and checked its function. Didn't check the tube to see if it was obstructed since it ran around the back of the engine to somewhere unknown...lol.

Planned on throwing new plugs into it but the coil mounting studs are super corroded and I was running out of time today, so just soaked each one real good with PB Blaster and re assembled everything. I am going to order all new mounting studs for the coils but I don't look forward to getting those rusty one off...sure hope PB Blaster comes through for me!

Fired the old girl up again and after revving her a bit to clear out the cleaner...she idles nice and smooth again!

Tip: Spray the PBlaster to soak overnight. Right before you drive it, spray again. Then when you get where you are going, spray again while hot. I did this on some 20yr old exhaust manifold nuts/bolts. Did that about a week, they all came off like butter.

Look into replacing the plenum gasket, it causes these sysmptoms and is a major problem on these engines.

Update: After going ahead and changing the Idle Air motor and seeing no changes (according to symptoms, it looked most likely cause), I finally got around to changing my plugs. I have had the truck for 2 yrs now and who knows when last time those plugs were changed but man, they were some burnt back ground electrodes! No wonder it ran rough! I also picked up replacement coil studs since they were so rusty, put anti seize on the tops so shouldn't be as much of an issue for future plug changes. New plugs and she purrs likes a kitten now.
Of course wifey reminds me that had I changed the plugs first, I would have saved us $130 for IAC...but oh well...lol.

While I was at it, I put a can of refrigerant into the non functioning ac...seems its all that needed :biggrin: All in all, a good day. I was hoping it wasn't a leaky plenum, for that was a bit of an involved job, so dodged the bullet on that one for now.

Well, it seems the symptoms are still there, but its really weird, for it runs perfectly at an idle of approx 650 rpm for the most part, just some of the time when I shift from drive to reverse, it causes the rpms to hiccup down to 400. It has quit on me twice since the plugs were installed. I don't have the radical ups and downs in rpm like I had before, just subtle changes and intermittently.

While I had it idling, I hooked up scanner and started recording the rpm while I went around and used the acetylene gas from our torches--I ran it around the throttle body to see if there was any change in rpm...nothing, no change, I would think this would indicate that the plenum gasket is not leaking..

It's an engine with 300K on it and it has that rattling/ticking noise that apparently is common with 4.7's, but I am open to any suggestions on this guys, for it sure is an oddball problem.