Need some help.have a 99 van 5.9 gas,1 ton.First off Recent repairs within last 3000 miles:
Complete tuneup
New Battery
New filters
New IAC
New ECM
New Fuel pump
New Coil
Was running down the highway 65 mph ,engine smooth and cool.Felt 1 miss as I accelerated to pass,check engine light blinked a few times then went off.just continued to lose power till finally I pulled over.unhooked battery for 10 minute and continued on perfect for 10 mile and it happened again.repeated this trying to get home 4 or 5 times.finally it wouldn't fix itself .It will starts cold, idles roughly 20 seconds then dies.To restart you have to floor it and crank for a few seconds and it'll fire but u have to flutter gas pedal to keep it running.lift and it dies.Exchanged the ECM for another one but still doing it.Any clues?Please?

 

Do the keydance…
On - off (don't start it) three times then to ON and leave it there.
If the check engine light comes on again, don't disconnect the battery - get the code first and then we can figure it out.

 

How many miles on the engine? It's possible it may have jumped time.

 

As stated above, get the code/s if you can, code readers can be bought reasonably cheap these days

Did a shop do the repairs for you or were they done by you?

I had bought and replaced the IAC on mine a handful of years ago, elected to go with new aftermarket rather than clean the old one which was an oem mopar part.
I did clean out the orifice pretty good before installing the new one. I didn't disconnect the battery first or do a initial pcm learn before starting up afterward. A day or 2 later began having hard starts and rough idle with having to feather the pedal to keep it running while in park and more so gear. Also was chugging and dying at stops, once it got rolling would be okay til the next stop.
I pulled the new iac out to check it and some of the plastic had broken and the plunger had come out of it's casing. I still had the old iac so cleaned it up good and put it back. This time had read here about installing and learning the new sensor it the right way. It's simply reconnect the battery, turn the key to on (not start) for 20-30 seconds then key off. Then you can start it up. Still running with that same old iac today.
There's something you can try

 

Yes, Doing the key thing 3 times did nothing for me when I broke down.And like i said the check engine light only flashed a couple times but went back off.Not sure if i can keep it running long enough to get check engine to come back on .Have a code reader but no stored codes.I purchased iac and tps from dodge dealer less than 3,000 miles ago .I had alot of trouble with van then that lead to all the parts,once I replaced ecm 6 months ago it fixed it.been perfect for 3000 miles.naturally my 1st thought was another ecm problem so it was warranted so I replaced it this week thinking it would fix it but no change.

 

Van does have 199k miles,but I live in wyoming where that really is normal.pulled cap ,distributor is tight ,spinning normal.And cranks normal.actually fires up up fast and normal cold.And dont think I could of temporarily fixed timing by unhooking battery cable .but who knows?

 

Unless the timing chain breaks, the distributor will still turn. With a helper, rotate the engine with a socket on the bolt on the harmonic balancer. Use a piece of soapstone or other white marker and mark the balancer timing mark in relation to the tab. Make a mark on the distributor where the rotor is pointing. Have someone watch the rotor while you rotate the engine backwards. See how far it goes before the rotor moves. I'll bet it moves 10 or 20 degrees before the rotor moves. That is the slop from a stretched timing chain. If you put a new timing set in it, it will really wake that engine up. I'd reaplce the water pump, hoses and thermostat while you're at it as they all have to come off anyway. With that many miles, I'd like to put a high VOLUME oil pump in t. Note I said VOLUME, not pressure. A high volume will compensate to worn bearings and get some extra miles out of the engine.