another thought... could you have a valve seat going bad? or a cracked head? the heads tend to crack between the intake and exhaust valves, although I havent had one myself, this is what I hear. I have had a valve seat go bad but it was 100% gone and the truck ran really bad. that turned out to be a plugged cat (2000 motor with the cats right next to the heads) causing excessive heat buildup around the head and ultimately the failure of the #8 exhaust seat.

2 things I'd try next, time consuming but as you said, "your at your wits end" so even if it doesnt add up to anything, at least you'll know the condition of your motor otherwise...

1) do the compression check on each cylinder
2) do a leak down test on each cylinder and see how long it takes to drop air pressure in each one and compare it to the other cylinders.
3) another thought that comes to mind is to slap a vacuum gague on there and when it runs like crap, try to isolate a perticular cylinder based on the drop in vacuum signal... might point you in the right direction.

when you clean the TB, pull the IAC out and clean it thoroghly and pay attention to the air holes/vents that are there. i've found mine plugged a few times and cleaning them helps alot (probably not your problem though).

another problem with these motors (again maybe doesnt apply here) is the timing chain stretches and throws off your ignition timing.
there is a cam postion sensor in the distributor that also goes bad...

just throwing out what I know at this point

 

hey another thing, not sure if it's been covered is the o2 sensor may have an intermittant short in it, read this in another thread a while back...

 

I unplugged the O2 sensor and it ran the same.....strange thing though, it didnt throw a code, even when unplugged altogether.

Yes, I may be headed in the direction of the compression and leadown test. Im gonna try the throttle body thing and a few others first.

I thought about possible cam or crank sensor issue. DO you think this could cause an excessively rich condition? I doubt the chain is stretched. The truck only has 30k on it, and the motor was replaced by dodge at 19k. It doesnt get driven much.

 

the o2 needs to be unplugged for a few miles before the code would show up... but when you mention that it runs the same w/it unplugged... are these sensors new? if so slap in the old ones for a while... the new ones could have a problem.

Also, the stock chain issue showes up after 30~40K and it has something to do with the sprockets and the need to keep the noise down on the motor... not sure if i remeber this correctly or not but I think they had nylon in there somewhere and that's what causes the loose chain. search for it over on DTO and you might have an answer on the what's & whys on it.

I wouldnt think a cam sensor problem would cause an overly rich conditon... most likely it would run like crap all the time. you mentioned that it runs fine off idle, which to me indicates that it's being masked in some way and you just cant tell it's having a problem still...

 

Just have a few questions. At the MAP sensor what are the voltages of each line(REF/SIG/GRD) when running rough, do they change when running smooth? Also have you hooked a vacuum gauge up at the MAP sensor to see what vacuum is applied? What is manifold vacuum at the intake when running rough, if it is pulsing please indicate from where to where?

We will start there.

 

I am getting a good 5 volt reference at all of the sensors. The ground has 60 ohms of resistance with the key on (.5 ohms off) The signal is showing about 1.3 volts when its running good. When it starts to stumble, voltage goes up into the 2.2-2.5 area.

The vacuum gauge is showing about 19 inches at a good idle and will fluctuate around when the idle turns bad...down to about 14 or 15 inches. But its not a pulsing. It just fluctuates with idle RPM.....as the car wants to stall, the vacuum reading drops as yo would expect.

I did some more studying of the data on my scanner yesterday. This time really focusing on O2 readings and injector pulse. The truck started out running fine. Everything looked very normal. THe O2 was bouncing and the pulse was about 1.8 ms. The idle started to break up and the O2 went LEAN this time, briefly. (This is new.) AS the idle started to worsen and stall, the O2 was real rich, like 1.2 volts and was pretty much staying there. The injector pulse was up to about 5-6 ms at times. The PCM was not pulling the injector pulse back though. There was no effort shown on the scanner to shorten the pulse width. Fuel was just getting dumped and the truck wouldnt even run unless I put my foot on the gas. Now, I looked back at all of my sensor info and NOTHING was out of the ordinary as far as the senosr which have anything to do with fuel mixure. The only one showing wacky readings was the MAP and I believe it was showing a low vacuum state because the truck was stalling out.

Now, if this were a GM, I would have thrown the PCM out the window and ran it over with my car. It just sounds like such an obvious computer problem. But, I know that these chrysler PCMs are pretty good. Plus, I have swapped this PCM into a known good running truck and the truck still ran good. The frustrating thing is that this is an intermittent problem and maybe the PCM was just deciding to be good at that time? WHo knows? I found a used PCM for about 60 bucks, so im gonna take a 60 dollar gamble on this thing. ANy other ideas are appreciated!

 

Of course, the used PCM did not fix the problem.........Im going out of my mind! If fuel is just getting dumped in with an injector pulse of 5-6 ms at idle, its gotta be some sort of electical issue, but ive just about worn my DVOM out checking everything I can think of.

The only thing slightly out of the ordinary is the crank and cam sensor reference is 7.3 volts as opposed to the 8 volts its supposed to be. I can see how this would flood the motor out though......

 

I feel for ya dude. I have a very similar problemwith my 98 Cirrus V6 2.5. Pretty much same symptoms. Replaced distributor, crank sensor, pcm, check all the sensors. See my post. Cold start is smooth and within 10 minutes its idles progressively worse until it stalls.
Temp guage Reaches second line always and then stalls. I'm going to check the AMP and Temp sensors at stall. Also read some forums where some guys had water in the gas. I'm going to dump the tank soon and put in fresh, this is my last resort. Peculiar thing is when it is getting ready to stall it puts a lot of water out the tailpipe. Too rich? Looks like spark goes away when it stalls. Good luck and let me know if you solve your problem. [sm=chairshot.gif]

 

The cam censor tells the computer when to shoot the juice, if its whacked, it might be giving a false reading and giving the PCM a reason to dump more gas at low RPM's. It also tells the PCM when not to shoot the gas, so if its whacked the PCM will have a hayday. Maybe it's voltage rises at higher RPM's? A combination of a weak Altornator field and cam and crank sensors? Maybe I don't know what I'm talking about...who know's I'm polish, what can I say.

I havd a similar problem with a 94 caravan, the crank censor went k-put and caused error codes for every censor but the crank censor, flooded the engin, wouldn't run worth a hoot and made me drink heavily. I changed the crank censor and everything went away. I also had another van with similar problems, it ended up being the censor below the intake port on the plentum. I don't recal the name at this time.