Hello, new guy here!
Car:1996 Volvo 960, 220k, 120k on replacement motor (allegedly)
Stars fine, idles about 950 rpm, shifts decent, goes down the road nice.
I have driven this car 200 miles.
Since purchase I did:
TB and SB; spark plugs; clean IAC; clean MAF; replace coil during the diagnosis phase detailed below.
No CEL except when the coil petered out.

Issue: Stalls when coming to a stop with brakes applied.
Symptoms:
1. If I coast to a stop, I can feel the torque converter lockup disengage (a little clunky, at about 5-10 MPH), at least that is what I think it is.
2. If I use the brakes to stop, the rpms will drop to about 450, at which point the car either stalls, or, if I am able to release the brake sometimes will catch and continue to run.
a. always starts right back up.
3. If I shift into neutral when coming to the stop, and apply the brakes, the gas pedal becomes non-responsive relative to motor RPM, and the stall occurs.
a. Sometimes if I time it correctly, I can get it to rev enough to avoid the stall in neutral.
4. No other stalling issues, just when braking to a stop.
Diagnosis completed:
I have searched for cracked or ugly vacuum hoses and fittings; I have sprayed MAF cleaner around all the areas that I could find with vacuum hoses; I have done a shade tree smoke test (blowing smoke into a vacuum port with intake sealed). No vacuum leak detected.
I cleaned the MAF, IAC, throttle plate, checked connections to the same, multiple times. Test light comes on on socket 1 & 3 on IAC. Again, no codes present.
I started to detect a faint buzzing sound, like that of a weak electrical connection arcing. I removed the knee bolster trim, and tried to locate the sound, which is irregular in interval and duration, and seems to change when motor is revved or brake is applied.
THE MOST PROMISING SO FAR: The focus on the interior white plastic plunger thing that is attached to the brake booster yields: when pedal held at not full pressure, but at various distance of pedal pressure, it sounds to me like a small air leak is present. However, we all know that a brake pedal makes that whooshing sound when depressed in normal circumstances.
Finally, if I repeatedly and forcefully depress the brake pedal when the motor is idling in park, I can cause the idle to increase to about 1200 RPM.

The Question:
What ails this car?

I appreciate any guidance, I have searched relentlessly for an answer, and now ask for help!

Colin

 

Update:
If I turn the car off while listening closely at the boot area of the brake booster (inside the car, driver's foot-well), the sound of air movement continues for about 5 seconds, then stops.
Is this a sign of a vacuum leak significant enough to cause the stall issue?

 

I think you should further explore the booster vacuum leak--it can definitely cause what you describe...
Why spray MAF cleaner all around?

 

Lev,
MAF cleaner is highly volatile. If there is a vacuum leak, the volatiles find their way to cylindar, idle increases. This could help identify existence/source of vacuum leaks.
But, do not try this at home, kids: major fire hazard. Others use propane torch, unlit.

Next options:
disconnect and plug vacuum hose at booster, drive and replicate.
disable torque converter lockup (anyone know how?) drive and replicate
Easy restart points away from fuel issue, but considering it.
Refresh auto trans fluid (doesn't look bad, but . . . )

I don't want to throw parts at this car. Does anyone have experience with this problem?

 

Update:
Pulled the hose off the booster, plugged with a bolt and a hose clamp. No change.
New symptom: Stall worsening, now will have UNRESPONSIVE PEDAL if I coast at 1800-2000 RPM. Stalling at coast, appears that it is unrelated to braking.
This still seems like a vacuum leak, possible.
Also, put a hose in the gas and heard the pump running, and also heard what sounded like splashing (return line?). This was similar to the v70 in the yard, but more splashy sounding.
NO CODES THROWN
Any ideas?

 

Further update-
checked the schrader valve on the fuel rail, fuel gushed out when running. 5-10 seconds after shutoff, no fuel comes up, so pressure drop.
At 1/3 tank, car would not restart. Ok, fuel issue?
So, pulled the pump, sock was off, there was about 1/3 tank of gas. (car restarted on about a gallon added).
tightened the connector on the pump.
No fuel in fuel pressure regulator vacuum line.

Questions:
Is there a check valve anywhere in this system to maintain pressure?
Is this bleed-down a problem?
Is this a failing fuel pump?
Are there other issues in addition to the failing fuel pump?
Evap purge valve?
STILL NO CODES

Any help is appreciated.

 

Ok, added about two gallons of gas and test drove it.
Seems like low voltage at the fuel pump, from the loose connector fixed it.
We will see . . .