94 5.0 V8. Engine runs well in cold weather. Starts very well all the time. When the engine warms up and the ambient temp is 75+ Deg F outside, the engine falters and tends to die at idle. I sometimes have to shift into neutral at a stop light and step on the gas to keep it going. It doesn't seem to have much power when this happens. It always uses a lot more gas than my full-sized van.

 

Change the ECT sensor.

 

It thinks it is cold out because the sensor is bad. Always running rich. Fix it soon or your cats will pay the price.

 

Buy a cheap digital multimeter & test the ECT (#36) key-on voltage across its 2 wires. Then test the ACT (#29). If either doesn't match the chart below, replace it.

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I tested both sensors. When the engine was hot (I let it cool a little so I would not get burned) #36 was about 4.6K ohms and #29 was 4.3K ohms. After the engine cooled off over night the sensors read 46.9K and 43.6K ohms respectively. The readings are in the ballpark, plus they are fairly close to one another, so I think there must be something else going on.

 

That sucks(those were the easy ones IMO). Bad idle control solenoid?

 

Then keep testing. The MAP sensor is known to cause weird problems like this, but it takes a tachometer to test it. If you can snag a few from the junkyards, it's pretty easy to temporarily connect them for testing. Also check for vacuum leaks (on the MAP's line & elsewhere) while it's running badly. Pull the red vacuum line off the FPR & check for gasoline (even the odor). Click my black Bronco in my sig, scroll to the bottom of the album list, & read the TSBs to see if any apply to your symptoms.

 

I think I found the problem. There was as break in the vacuum hose from the charcoal canister to the purge solenoid valve. The break was hidden under the thick hose going to the thermactor air pump. I will have to run it a few times on the freeway, pulling off, stopping and then restarting to make certain that actually cures the problem. Thanks for all your help so far.

 

That should have no effect, other than allowing unfiltered air into the engine. Even sealed, that line still pulls air thru the carbon canister as if open (when the CANP is ON).

I'd keep looking.

 

I have a 93 F 150 4x4 with the 5.0 and I had the same problem. It would run like a champ when cold but have a rough idle and stall when the weather got over 75. I'm not sure what codes you pulled, but mine was showing a code for the IAC ( I believe thats what it was called) Anyhow..... I pulled it off.... squirted a little break clean in it and wah lahhhh It runs fine. No stalling, no surging idle. Might want to give that a try. It worked for me

 

I don't know where the IAC would be located, but I did squirt carb cleaner in several parts of the the engine while it was running. I generally only run the truck once every two weeks when I pick up a load of bread for the animals on my farm. It's about a twenty-five mile trip one-way. The engine surges and tries to stop when I restart the engine after loading the bread. By the time I get home where I can check out the engine again, it is running fine, holding a steady idle.

 

I have the same problem. My drive is 45 mins and it will stall at least once. I have a can of cold spray now. Last nite it stalled at a traffic light and sprayed the spark module and around the distributor area and it started up. I'm going to try this a few more times before i say it could be my problem.
I have an 89 with 4.9L. The module is manufactured by wells.