My 96 6.5 has been stalling lately, I'll start it up and it will be a rough idle going low to 500 rpms then up to 700 then down or it will just stall. It seems to do it right after start up most of the time but once or twice it has happened 10 or so minutes after, but once its warmed up it seems to be fine.

The truck is totally stock and as about 310,000 kms. I don't expect and exact solution but soon its going to the diesel mechanic and I was wondering if this is going to be costly.

Thanks

What have you changed lately?
Fuel filter? air ?
does your liftpump operate?

Well I took it to the shop but the diesel guy is on vacation, so I don't think theeyre experts on these trucks, but the air filter was terrible, and the Liftpump didn't work so they replaced the air filter fuel filter and Lift pump(nice call QM) charged me 490$ for it and it seemed fine and it seemed to start better, so a day after that (today) it worked fine for three 20 minute drives but in the night on the way home from work it started stalling terribly, you start it and it just stalls again within 30 seconds, so I Let it sit for a half hour and it seems to be running fine now.

Any other ideas? I'm hoping its not the IP. Had it replaced under warranty and I saw the price.

Oil pressure switch is bad. Yea I know your gauge works. The thing also operates your electic fuel pump. 30 bucks from NAPA

490? Makes me glad I take care everything myself.

test the liftpump connector for 12v to see if OPS is working.
Bad PMD? The only test for this is to try another to see if it cures the problem.

Dan is probably right, OPS is terrible design to begin with and I wouldnt even bother replacing it, run a hot wire to a switch on the dash and down to the pump, or from a circuit on the fuse box thats hot with the key on.

The mechanic replaced the PMD/FSD and it seems to have cured the problem, but some of the times it stalled and the truck had been off for two hours or more, and it stalled right at idle, this is what I don't understand because the PMD wouldnt be hot then would it?

But also while driving with the fan on full heat it didn't stall either. Would that cool down the PMD much?

heat is not the only PMD killer, you could put it in an icebox and it would still fail eventually, heat just seems to make them deteriorate more rapidly.