Odd situation that just recently popped up. I have replaced many parts on the 97 discovery starting initially with head gaskets. New coil wires plugs etc. Purchased a basic Wagner MAF when I was troubleshooting an engine miss. Turned out to be injectors …I have also installed new fuel pump and filter..and CPS. The IAC was replaced and also swapped the TPS after the stalling started.

The truck runs fine but after it’s warmed up and left idling for a few minutes it will stall when the engine is under load (in gear). And eventually stall in park as well. It stalls to the point that the engine will stumble and shut off intermittently.

It acts like either the fuel is shutting off or loosing complete ignition system, it will not recover with the throttle. When the MAF is unplugged it does not stall but tends to overheat .. ? Very odd, doesn’t overheat while driving before the stalling eventually starts occurring while the MAF is plugged in.

I ordered a new MAF and I have another fuel filter I can use. When it starts stalling the exhaust smells rich / sulfur aroma. Not sure if it’s just running super rich or a cat may have failed.

And yep it has almost 200k miles. Runs strong until the stalling commences.

Thoughts ?

 

Sounds awfully like a crankshaft position sensor. You might have nicked ore pinched the harness for it also while doing the heads

 

Do you have a way to reset adaptive values? It usually needs that if TPS was changed or even moved. Maybe IACV needs the reset too, but maybe it resets every time the key is turned On then Off.

Did you clean up the throttle plate and IACV passages? They can get very gunky. How are your crankcase vent port and PCV hoses? Probably fine since you did the head gaskets.

Can you measure fuel pressure? Make sure vacuum tube is sound for fuel pressure regulator. A busted or disconnected tube can cause rich burn at idle.

Can you read O2 sensor voltages real time? Both upstream sensor voltages are the first thing I look at to ensure good engine function, along with Long and Short term fuel trims. Running lean can cause hotter combustion temperatures. Running rich can be stinky at idle. Both rich and lean can be seen at the O2 sensors.

 

Thanks to both. I still have the original CPS and considered re-installing it. Honestly it was just a trial and error approach to resolve an engine miss.

I have not reset the adaptive values, without a dealership visit I’m not sure how to. I have a LL handheld but I don’t think it will do the reset. I did replace the post cat o2 sensors early on, have not replaced the pre though. Both the IACV and the TPS were changed in an attempt to correct the stalling, so those efforts were after the problems started.

 

Could be a vacuum leak causing it to have a low idle and stall. Upper Intake/plenum good and tight? Get yourself a cheap 20.00 Bluetooth OBD2 and if you have an Android the GEMS Reader App. It will allow you to reset the Adaptive settings.

 

+1 on GEMS Reader App. Also get Torque app to read O2 voltages real time, they can show if you have a vacuum leak (fuel trim values will go very high). Torque will also show the fuel trims. Both apps are super cheap, the GEMS Reader might be free.

If the throttle stop lever got tweaked, you might need to reset your base idle (there's a screw to adjust). But make sure no vacuum leak first. What did you use to seal the intake plenums?

If CPS was faulty, the engine would not run at all.

 

Are there any codes?
Can you read IAC values?
Have you ohmed-out the temp sensor (and compared readings with an ohm/temp table)?
..a drifted temp sensor can 'fake' the computer into thinking it's the wrong temp and goof up the fuel.
You did inspect/clean the throttle body for 'gunk' and build-up? And cleaned with a plastic brush? I assume so, but just asking.

I agree, put a vacuum gauge on it and read what it's pulling, and the needle behavior. You can learn a lot (maybe).

 

Mine was “stalling” after warming up but it was more like a hiccup, RPM drop and power loss then it would come back, only to “hiccup” again and would repeat that until I turned off the vehicle. However, mine never died. Turns out mine was a bad VSS or vehicle speed sensor. Do you have an ultra gauge? Any messages from it? Codes?

 

Thanks - I replaced the mass air flow sensor (again) and it hasn’t stalled since. Need to get the idle nailed down now because I had replaced the IACV and TPS chasing the issue down. Oh well always learning with one of these LR.

thanks