While we are investigating this timing and high intake temp issue we are doing a few things we didn't do along the way; like we now have replaced the pickup coil, made sure the little strip it contacts with looked nice and clean. Didn't seem to have any effect.
Now we have the top of the throttle body off, (some of you in this thread mentioned that early on, but we only looked down in it and didn't take it off before) and will clean it and replace the gasket. It doesn't really look that bad to us, but what the hey, it might as well be clean and have the new gasket.
Our son said while that's off, maybe try cleaning the injectors at the rails. He did a fuel pressure test for us since he has gauges for that, (pretty sure he already checked that for us at some point, this is getting hard to keep track of ) and it was good.

Dang timing chain is going to be a pain for us to do ourselves, so we really really don't want it to be that.

 

At 75,000 miles on the engine, I doubt it's the timing chain. 15-16 inches of vacuum is a little low but not overly so. I like to see 17-18. I'm trying to remember what all you've done and how it dies. When it dies, does it sputter and sort of expire or does it just shut off immediately.

 

It doesn't sputter. After everything we've done, here is the current symptom: On two test drives in the neighborhood, it just died when coming up to a stop sign The idle reduced nicely like you;d expect when slowing to a stop, but it just dies. Idle sounds great, it starts right up without having to rev it, it accelerates as we expect it to. Tomorrow we will drive it around a good bit, compare how it does running cold and then after warming up, and see what we get.

Maybe the computer had not really relearned well enough after replacing the cat (we also replaced both 02 sensors, returning the one we had and getting to Dense brand as someone else here suggested) so tomorrows test drives may tell a different tale.

Also we will do another live testing with the obd scan thing, see it the air intake temp is still high.

It's still worrying that we have had no codes and no check engine light except when we ran it without an 02 sensor, and once when a plug wire was pulled off while it was idling (oops).

 

I had a '93 Dakota that would do that from time to time. The first time, I took it to the dealer under warranty. This is going to sound silly as much as you've done to it, but all I did the second, third and so on times was clean the throttle plate. If you haven't done this yet, try it. Take the air cleaner assembly off and spray some throttle body cleaner down the intake throat. DO NOT use carburetor cleaner unless it's specifically stating on the can it's safe to fuel injection systems. Gummout used to say on the can to NOT use on F.I. systems. Use a paper towel to rub around in the throttle plate opening below the plate. You'll get all sorts of gooky stuff (<----fancy technical term) on the towel. Any paper will burn right up unlike some cloth towels if a piece comes off. The gooky stuff (<-----there's that fancy term again) comes from the PCV valve system and is a normal function. Reassemble everything and start it up. It WILL run like poo for a bit. (Got to keep it clean here.) It may even be a bit hard to start. Once it smooths out, it should quit dying. Build up on the plate causes the idle to drop too low. If you can come to a stop with your left foot on the brake and a slight throttle pressure with your right and it doen't die, give the cleaning a try.

 

When you have everything reassembled, (and hopefully you had the battery disconnected while playing under the hood.....) hook the battery back up, turn the ignition to "On", not start, count to ten, (don't touch anything during this period) THEN start the truck. It gives the PCM to re-learn the zero values for various sensors. It *should* start right up, and idle reasonable well. (unless there is some other underlying problem that hasn't been addressed yet.)

 

Well this is getting so frustrating! Really good test drives yesterday, but now today problems again. Grr.

First off, to answer you guys, yes we cleaned out the throttle body, and replaced the gasket, It didn't really look carboned up, but cleaned it anyway. We doubt there is any gunk down inside the intake. What we can see looking down in looks normal. But we may do a quick leak test around it with some spray.

To reset the pcm we had been using another procedure, (and yes unhooking the negative on the battery before changing any parts) by turning the key to on and wait till the lights go out, repeat that 3 times, then start up on the 4th time. But HeyYou we will try your do it once but wait 10 seconds as well.

We also changed the oil and inspected it, it looked pretty normal, nothing in it that shouldn't be. And we may as well replace the PCV valve, although we had cleaned it out and inspected it and thought it was good.
We will take the dang thing apart to get to the timing chain if we rule everything else out, but it's a real pain on these vans so would prefer not to have to do that since we have no other symptoms of timing chain, no noise at all, no misfires, no metal showing in the oil.

But now the newest frustration:
Yesterday we drove probably 50 miles around town, stop and go, stop at stores for up to 20 minutes or so then back on the road. Stopped back home and went out again after a while. Idling at long lights, going around neighborhoods and out on a 6 lane highway. Starting from cold engine and starting from warmed up. The van started and ran so beautifully it was a pleasure. Perfect idle, no accelerator hesitation, no misfires, no surging, no odd noises, it was just plain wonderful. But....................
TODAY....... First time we started it, it stalled right away in the driveway several times, when it started up and it seemed like it wanted to die he revved it and it surged up higher on it's own. Once that leveled off and stayed running, we went on a few errands and it kept dying along the way, while driving. A few times while coming up to a stop, when going up a driveway, or after pulling in a parking spot. Once while idling at a light. It seemed slightly rough a few times when accelerating, other than that no surging or misfires or odd noises. This stalling kept up the whole time we were out, even after the engine warmed up. And it is just dying suddenly, no change in the engine noise at all, just suddenly it's dead. No matter whether the A/C is on or not.
It will start back up again, after anywhere from 2 to 5 minutes later.
One odd thing we noticed: although the power appears to stay on after it stalls (power windows work, clock is still lit up) the key buzzer does not sound when turning the key to on. When we turn the car off normally the key buzzer will sound when we start to turn the key, but if it has stalled there is no buzzer when we turn the key.

We are again wondering if the PCM is starting to fail and doing erratic adjustments and shutting down?
So we have questions. Maybe this is one reason we have had no real codes?
We are going to take it off and give it a visual, look for any wire issue or anything burnt or charred. But when we went to take a look at it, it's so hot we can't touch it, even after the van has been sitting for a while. It seems hotter than anything else under the hood. Put the infra-red thermometer on it and it shot up to 160. Should the PCM be too hot to touch? We've been working on this van since 1999 and have never noticed a lot of heat coming off that area.....
I have read that a faulty PCM can make many of the symptoms we have, but also have read that people replace the PCM only to find they still have not found the problem.

eBay seems to have stores that will check a PCM and repair if needed, other stores I find online sell new or remanufactured ones and say they program the VIN in and update them so they are plug and play. Other places say you have to take it to your dealer to have the VIN put in.
We are reluctant to try the repair route, even though it can be half the cost. But do any of you have any experience buying these online or having repairs done?

We are about at our wits end.

 

Think I would replace the PCM...... It shouldn't get that hot......

 

I agree too, that the PCM is probably bad...Ive felt mine before after a long run and it isn't 160
Or something else weird like a clogged fuel filter, bad gas, intermittent fuel pump, kinked or damaged fuel line, vapor lock, or even a screwy battery.

 

Contaminates in the gas?? (water....)

 

this van has no fuel filter, we drained the gas, saw nothing amiss but put fresh gas in, fuel pressure was good tested a few times, not sure if that would catch an intermittent fuel problem; vapor lock? Is that likely on a fuel injected vehicle? battery is new.
Last thing we did is spray around the intake manifold checking for possible leak, all was good there.