Hello,

5.0 / 302 in a '99 all-wheel drive mountaineer / explorer suddenly started exhibiting intermittent symptoms:
- stalling when coming to a stop
- hesitating and/or jerking when accelerating from a stop
- idling high (1k or so in Park)

Diagnosis & work so far:
- Check engine codes; none present or pending.
- Check vaccuum pressure. No identifiable issues with a warm engine in park.
- Fiddle with vacuum hoses, attempt to expose leaks, etc.
- Check / clean throttle body.
- Install new Idle Air Control.
- Verify correct voltage / function of Throttle Position Sensor.
- Flushed all transmission fluid and installed a new filter. Lucas slip-stop was added a couple of months before this started, but now the ATF is clean.

It still runs rough at times, but runs great most of the time. Occasionally will die when in gear and stopped.

A vaccuum gauge shows that in park and neutral the vaccuum is within normal specs, but sometimes when in Reverse and Drive, drops to around 15 pounds or so.


Because the issue is primarily in Park and Drive and is much more pronounced in these gears, I wondered if it's a Lockup solenoid in the transmission / torque converter. However the occasional rough idle and frequent high idle in park makes me still suspect a general vacuum leak.

Any thoughts?

Thank you!

 

The whole powertrain in your vehicle is computer controlled so first thing you need to do when diagnosing a problem is pull the codes.

 

 

I'm not too up on OBD-II stuff, but I think a converter lockup problem would throw a code. You might take a look at the intake tube from the airbox to the throttle body, does your truck have the MAF in the airbox and the air intake running along the top of the radiator? I've seen one Explorer with symptoms similar to yours that had a hole worn in the bottom of the intake tube and sucking in air after the MAF. Just a thought...