Near End of Life! Please Help!

[Meridivs]

Our trusty '92 Pontiac TS 3.1L V6 has developed a bad case of misfires while hot. It's like the engine cuts-out for a second then recovers and so on until it eventually stops. In higher revs it's usually ok but sometimes the rpm just drops.

Nothing we've tried so far had any effect:
- changed the whole distributor assembly with ignition-control chip and new pick-up coil
- changed the ignition coil
- tried another engine computer/ECU
- spark plugs are original ACDelcos and new
- spark plug wires are new
- Idle Air Control valve is new
- every other sensor checked-out ok

We're at the ropes-end with this one.

Any ideas on what we could try before throwing in the towel?

[1QUICKHATCH]

How are your ground wires? Compression test? Have you confirmed timing with a timing light?

[Meridivs]

Ground wires look in order. Latest compression test was ok - the issue is random, sometimes it keeps the idle, sometimes it drops to 0 rpm, the mechanic says it could be something electric/ignition-related but we have no clue on what to check after changing all the parts. Timing is all-right, checked with a timing light by the book (GM Service Manual).

Just changed the EGR valve with a new Delphi unit, no effect - engine maintains idle until gets hot then just starts to misfire until it dies.

One way to keep it running is turn on the AC. The ECU climbs the rpm to 7-800 rpm and that seems to "fix" it but it would be very helpful to know what could cause the rpm to suddenly drop on these engines.

I have attached a sample audio file with engine running.

Any other ideas?

[Purple pit]

Have you checked the crank sensor? Mine turned out to be ok, it was the wires. They were bare at the plug for the sensor! Not sure why but the car ran just fine when cold. Once it was hot it would cut out. I mean die for second and then act as nothing had happened(when driving). High rpm had no problems.

[Meridivs]

Do you have any idea about where this sensor is located on a 3.1 V6 engine? I found it in the parts catalog but can't find it on the engine...