My SHO stalls intermittently; why?
A somewhat common and difficult-to-diagnose problem with SHO's is intermittent stalling, especially at highway speeds. SHOtimers have identified a few areas to check.
Crank and cam position sensors
Stalling is often caused by failed crankshaft and/or camshaft position sensors. Failures of these sensors are many times heat-related; however, failure of the crankshaft position sensor can also be caused by a leaking water pump. Coolant can leak from the pump onto the sensor, and then down onto the catalytic converter where it evaporates, leaving little evidence of the source of the problem.
A textbook symptom for this problem is the tachometer reading dropping to zero while the engine is still turning. The tach gets info from the DIS system. If the engine dies due to a fuel concern, the DIS system will still be trying to run the engine. Since the tach is going to zero, then that tells you that the DIS system is not running the engine.
MAF sensor connection
Dirty connectors on the MAF sensor can cause stalling. To check, disconnect (and clean if necessary) the MAF sensor connection when the car stalls. If the car starts back up, that's probably the problem. Extreme cases may require replacement of the connectors.
Aftermarket chip connection
Another cause of stalling if the car is equipped with an aftermarket chip, is faulty or deteriorated connections between the chip and the card in the computer. This can be fixed by removing the chip, cleaning the contacts, and reinstalling the chip.
MAF Connector and/or Speed Sensor
Lee Hassig was experiencing this kind of stalling: When slowing to a stop in any gear and disengaging the clutch, the engine would slow way below idle speed -- down to about 500 RPM. Often it rebounded to idle speed, but occasionally the engine would stall.
The drop in idle speed and stalling only happened when using the engine (along with the brakes) to slow the car.
After extensive diagnostics two codes came up. One pointed at a faulty MAF connector (F43Z-14A411-A), the other to a bad speed sensor (F43Z*9E731*A). Both were replaced, et voila, problem solved. Engine speed now pauses at 1,100 RPM before falling to idle at 950 RPM or so. No sign of stalling.
If you are having trouble starting your SHO combined with intermittent stalling, check out George Fourchy's writeup on Battery Terminals - one of the most common reasons an aging SHO will leave you stuck.
Idle Reset/Relearn Procedure
Always make sure to reset your idle after disconnecting the battery, as otherwise stalling and surging can occur.