"It still could be a bad FPR. It does not have to leak from the diaphragm and into the vacuum hose to run rich. The FPR could not be returning enough fuel back to the gas tank.
This can happen if the FPR goes out of adjustment internally, the ball and seat get sticky or the return line gets restricted.
These issues with the FPR are the flip side of what can go wrong with them and are more rare."

I realize this is a thread started last summer with no resolution posted, but being revived here, Machine Man, your message above caught my eye, and I wanted to include my recent experience to prove exactly what you said is possible and true.

Subject car is also a '93, like Joe's, with AW-70 auto transmission. It is my #1 daughter's most recent 240, her third. She did not mention poor mileage, but did find the idle erratic and stalling occurred on decel to a stop. She took the car to the Volvo dealer who she had replacing her AC compressor (another story) but they thought her cat was clogged. Surprisingly (to me anyway) the dealership service manager recommended she get the cat replaced by Midas or Meineke as "Volvo didn't make them any longer" so, by the time it arrived at my garage, I was skeptical. My guess is the tech she trusted who "drove a 240" no longer worked there.

Sure enough, the cat was a little rattly, but it didn't fit the symptoms. I checked, the cat was available "Genuine Volvo" for a little more than $100, nothing like that $900+ they used to list for, and of course Volvo didn't make cats for 240's, they bought them.

I took the car for a drive, and sure enough I needed to "two-foot" it at the stop signs. My daughter never learned to do that, but my life has included many cars which occasionally needed this "skill," manual or automatic, to keep them from stalling.

A clogged cat is a problem I'm familiar with. I know the sound of the exhaust. Even the rattle sound the cat makes when tapped with a rubber mallet is distinctive. This car had other troubles.

Idle trouble in a car I have not maintained makes me think throttle body service, so that's where I looked first. I pulled the AMM hose to look, but all was immaculate. None of my cars was this clean for blowby. I pulled the idle valve -- same there too. Clean and dry. I can test them with a variable pulse width tester, so I did, and there was no reason to suspect the idle air valve.

Codes were clear except for a 231 - mixture out of range at part throttle. I put a meter on the oxygen sensor. It seemed stuck rich, but would cross stoich and spend some time lean, as if it were hunting hard. I pulled the FPR vacuum hose and teed in a vacuum gauge, and once again I was envious -- a steady 20 inches. Nice engine.

My daughter mentioned hearing something like someone was using a hedge trimmer nearby, but coming from the car. I couldn't hear it. She thought it was coming from under the car. In its recent history I replaced the tank sender and pump, so I ran the pumps from the fuse panel without the motor running. When I ran both, she could hear the hedge trimmer. Now I could hear what she heard, but it was not the sound of cavitation in the main pump, it sounded strained.

My first thought was maybe the fuel filter was clogged, so I put the gauge on the rail. Yes, this is a '93 with the Schrader, but like the OP here, I know by experience I'll get a fuel shower if I use a stick gauge on the rail, so I just used the one I've always used on the line fitting. Surprise!



Replaced the regulator, and we had full agreement the hedge trimming neighbor disappeared, and the test drive proved a huge improvement.



It was a surprise to me, because I'd only seen one stuck regulator before, and it was the kind used in LH2.0. Its small spring had rusted. I'd never heard of the kind used with LH2.4 sticking closed, so I was eager to see why.







I found the small spring loose outside its well under the valve ball, and to this day I don't understand how it performed its Houdini escape trick. The next surprise came when I saw how expensive these FPRs had become. The one on my shelf cost $39. The one to restock was over a hundred now.

--
Art Benstein near Baltimore

"If you send me $20 I'll send you a how-to explaining how to make $20 from people on the internet."