1997 Skylark 2.4l 4 cyl, 90K miles. I'm experiencing intermittent start-then-stall and rough running. It previously had Passlock issues, but I worked on those, seemed to get them resolved, and this just feels different. Instead of immediately shutting off when Passlock kills the injectors, it'll run rough for a couple seconds, and then die. I have to give it 30 to 40 percent throttle, and it will stay running (sometimes), but stumble and surge. It might stall out, or after 10 or 15 seconds of running rough, it'll stabilize and be fine until the next time I turn it off and restart. No codes set, at least that I can get with my $40 scanner.

I was thinking IAC valve, but with the throttle open, IAC valve should be out of the equation, right?

Perhaps fuel pressure, but there'* no fitting for a fuel pressure gauge unfortunately.

Everything else I can think (crankshaft position sensor, coil packs) shouldn't magically "fix" themselves after 10 seconds, should they?

My A/C compressor clutch pulley is making a terrible racket, too, so I'm pretty sure the bearing is shot. Any chance that could be causing resistance or slipping on the serpentine belt, causing these issues?

I'd appreciate any thoughts or advice! Thanks!

Any chance if you know if this is the original fuel pump? I'm skeptically wondering if you really do have a schrader valve to check fuel pressure.

Anyhoo, try disconnecting your MAF sensor and see what happens when you start it.

Yes, it is the original fuel pump. The in-line fuel filter has been changed, but the problem existed before the change and hasn't gotten any better after.

Everything I've read about the 2.4l Quad 4 engine and this car says no schrader valve on the fuel line, though I would be tickled pink if someone can prove me wrong.

I'll disconnect the MAP sensor (no MAF on this car) next time it acts up and see what happens.

FWIW, I did replace the IAC valve and MAP sensor previously, when I was shotgunning parts at what turned out to be the Passlock problem. Though in retrospect, that may have bit me in the rear, since they were OEM parts and I replaced them with aftermarket.

If this had a schraeder valve, it would be on the fuel rail......but if I remember right, it doesn't ....you need a special tool setup, whereby you disconnect both fuel lines and install shutoff valves...one of the valves has a setup for a fuel gage....

One thing I would check, is pull the vac line off the f/p regulator and check for fuel in the vac line...if there is fuel, you need a regulator...

Another thing to try, is remove the f/p fuse.....crank vehicle over to relieve all fuel pressure....now have someone crank the vehicle, and spray carb cleaner into the intake.....if the car runs ok while you spray, you know you have a fuel delivery problem....

Definitely no schraeder valve. No fuel in the fuel pressure regulator vac hose. Started and ran, didn't see any leak out of the regulator with the vac hose off either. Regulator was replaced 2 years ago, too, after a massive leak, so hopefully it'* still got life in it. Will continue to monitor that possibility, though.

Of course, this morning it starts right up. Will have to wait for it to act up again to check with the MAP sensor unplugged.

Does anyone think that A/C compressor could have anything to do with it? I know the compressor has a refrigerant leak, and the bearing is shot, so I'm looking at replacements there. I'd love to have that fix the starting issues too, though I'm pretty sure it won't. I'm wondering if I'm getting into "money pit" territory.

Not the MAP sensor, the MAF sensor. Mass AirFlow

MAF (mass airflow) sensor doesn't exist on this engine.

Since the weather got a bit better, I've been able to spend a little more time troubleshooting.

Been stalling out and then starting fine on the second crank, running fine after starting.

Still no gas in the fuel pressure regulator vac hose, but definitely a gas smell in the hose.

I hooked it up to the iPad today, and found short term fuel trim % is running in the 0 to -5% range, but drops to -15% to -20% when throttle is applied. So I'm starting to think it could be a minor failure in the regulator. Not enough to cause a leak at idle, but when vacuum is pulled, it'll leak.