There are numerous posts in this site, including my own, regarding the infamous codes and bad idle issue. After trying everything e.g valve adjsutment, coolant bleeding, tune up, upper plenum cleaning, egr etc. I finally got to the bottom of it. Low compression 60lb on cylinder 4 on the 3.0. I couldnt believe this car would have a cracked ring considering it's low mileage, regular oil changes and adult use but as they say "bad to hear but good to know" Because now, I can quit soliciting advice on this forum and live with it or fix and quit wasting time.

Surprisingly the V6 or now more appropriately the V 5 & 1/3 runs great at any speed higher than idle. The idle is lopey when warm but really kills with the AC on. Thank God, I line in MN. I tried a Marvel Mystery Oil overnight piston soak, that actually raised my compression from 165-70 to 190-200 in my good cylinders!!! but number four is stuck at sixty.

I frequently drive the car at 75-80 with no problems sans blowby and oil consumption of 1 quart every 500-800 miles. In fact my son just drove the car to Wyo and back in this condition. I am assuming that it's obviously not going to get any better on it's own by it dosent seem to be getting worse.

My thought is that because the car is running on such tight parameters at idle that there isnt much room for error at idle but a higher rpms the problem isnt so acute. We'll see.

My advice to all who are having this probelm is do a compression test first before you waste a lot of time and $ on the wrong fixes.

 

You can try a leakdown test to figure out if the problem is with the valves, head gasket, or the compression rings.

 

I give a squirt of oil and it goes to 130

 

This is one of those times a difficult decision must be made; 1-cylinder repair, remove/replace/overhaul engine, or live w/ problem. Only you can make the choice.

A 1-cylinder repair would require removal of intake manifold, cylinder head, removing oil pan, and releasing connecting rod on weak cylinder to allow rod and piston to be removed. You could find cylinder wall damage that makes this repair impossible, but if cylinder is OK, then new rings may allow a repair in place. A big job, but less work than pulling/replacing engine.

Also suggest a leak-down test to confirm ring damage before undertaking any repair. If only a valve is damaged, repair is much easier. Lot's of good videos on youtube about how to perform and make your own leak-down tester.

good luck