Engine Stalls at idle

No, I forgot to mention, no engine lights, no Codes. I have a simple code reader.

Since my other reply, I removed the plastic intake plenums. I thoroughly cleaned them and cleaned and degreased the gasket surfaces and channels. I replaced all of the Plenum gaskets. Pre-coating the gaskets, gasket surfaces and channels with a moderately thin coating of high temp Silicone. Reassembled and torqued properly. Then I let the vehicle sit for 24 hours to give PLENTY of time for the silicone to cure.

I double checked all vacuum hoses and connections. I'm hoping those steps eliminates any vacuum leak concerns.

The battery was disconnected during that entire time.

When warmed up it would stumble at stop lights which was an entirely new symptom. I swapped the hoses for the DPCE and that symptom disappeared

I tested it by sitting stopped with the parking brake on and in drive lights on, for about 10 minutes. It died after about 10 minutes. Upon restart, putting it back in drive, the rpm settled at approx. 750 rpm for about 20-30 seconds, then dropped to approx 600 rpm. Then it died a few seconds later.

That same pattern would occur every time once warmed up and stopped in drive the rpm would go to around 750, then drop to 600, then some times the engine would quit after anywhere from a few seconds to a few minutes.

"Does the engine slowly sputter to a stop, or is the stalling immediate? "

It is immediate as if someone turned the ignition off.

I checked the voltages and resistances as follows:

Engine off cold.

- Bat terminal to bat connector = 0 ohms 0 vdc
- Bat connector to body = 1.3 ohms 0.001 vdc
- Bat connector to Block = 0.3 ohms 0 vdc

+Bat term to bat connector = 0 ohms, 0 vdc
+Bat connector to Alternator = 0 ohms 0 vdc
+Bat to + on Maxi Fuse = 0 ohms, 0 vdc

Engine on in drive, warmed up, lights on, after engine has stalled in drive

-Bat connector to block 0.148 vdc
-Bat connector to body 0.042 vdc

+Bat Connector to Alt = 0.224 cooling fans on, 0.139 cooling fans off.
+Bat Connector to Maxi fuse 0.042 vdc

"Last, check the PCM power relay for proper operation. It may be getting hot, or the contacts are bad, causing the PCM to lose power and thus, the engine dies."

That relay was warm, but not markedly warmer than some of the other relays. The coolest relay in the box was the one that was in the start interrupt position. I swapped the relay that was in the PCM slot with the one in the Start interrupt slot.

The relay swap was the last thing I did before coming in and writing this. The Windstar ran parked in drive with the parking brake on and chocked for about 5 minutes without stalling after the swap. I do not consider that an adequate test, so will take it out for a test drive a little later this afternoon.

Just got back from a short term test. I drove about 10 miles in city traffic. Stopped about 20 times, and it did not stall. Then stopped in the drive way and let it sit in drive for about 10 minutes, and it did not stall.

Next will have to be a bit longer drive, but hopefully swapping the PCM/Start interrupt relay's cured the problem.

Back from another test drive and the news is not good. Didn't get 2 blocks before it died at the stop sign. Then it ran ok through 3 more stops. Then at about 40 mph it started "bucking" Then it died as I turned a corner. And again when I pulled into a parking lot.

On the way back it started bucking again at around 40 mph, and gave two codes P0340 Camshaft Position Sensor Circuit Malfunction and P0401 EGR Flow Insufficient Detected.

Now that could be caused by the hoses connecting to the DPFE hoses being reversed, but I did not get a P1403 DPFE Sensor Hoses Reversed.

So looks like the next thing to replace is the DFPE. But before I do that, I'll remove the vacuum to the EGR valve and plug it and do another test drive tomorrow.

I have access to a OBD reader. Here is the link to the instruction manual for it.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Let me know if it will be of any use for this problem

CORRECTION

The TPS was NOT replaced. So I changed it this morning and did a short test drive with no problems. Longer trip later today.

Did a test drive this afternoon during the heat of the day 84 degrees F. Didn't even get 1 mile before it died at two stops. It also stumbled a couple of times at about 40 mph, and once at about 10 mph turning a corner.

Disconnected the vacuum line to the EGR and plugged it. Then took it for another test drive. It didn't die at any stops, but still stumbled a couple of times.

I'll run the scanner and check.

I recently read some disturbing articles on Windstar transmission failures. Some have stumbling symptoms as well. What are the chances that it's the tranny?

I'm going to do a fluid flush and filter change, just cause it wouldn't hurt.

Did the filter and flush. Paid extra to get the proper fluid. No change.

Read that the alternator can throw ac spikes that confuse the computer, causing the P0340 code. Disconnected the alternator from the electrical system and took a test drive after clearing the codes.

The vehicle still stalled and bucked. That does not rule out that the alternator is still affecting the P0340 code, but it does eliminate spikes from the alternator causing the bucking and stalling.

I also noted that the bucking seems to only occur during steady state throttle settings. The bucking will stop if I apply throttle. Trouble is, that could just be coincidental. The bucking could be short term, and by the time I apply throttle the bucking may have quit on its own

Verify I can test the MAF by disconnecting it and running the vehicle.

No, I have not tested the TSP. Just assumed it was good since it was new.

Ran it without the MAF connected till it was warmed up. Once warm the stalling occured, but no bucking that I noticed.

I'll test the TPS next.

Just came back from an Alternator/Starter shop. They tested the Alternator, and it is not thowing AC spikes.

It started bucking and did it long enough to apply a steady increase in throttle. The bucking continued untill I had increased the throttle about 25% So it's not a steady state problem that only occures at a fixed throttle position.

"turn the key on engine off. You should see.8 to 1 volt with throttle closed.

0.946 vdc

"slowly lift the throttle and watch the voltage it should slowly and steadly increase with no drops or glitchs."

Smooth increase in voltage

"at full throttle you should see 4.5 to 5"

4.54 vdc.

Looks like it's not the TSP.