Hiya folks. I know this is my third thread, but I've done a bunch of work and cleanup and I have just about exhausted all my options - I have exhausted the things I thought most likely.

CPS Replaced w/new from IPD
RSR Replaced w/good used
RSR Wiring pigtail replaced w/good used
Bypassed RSR with a wire splice

Ignition power stage (ignition amplifier) replaced w/good used
Ignition power stage thermal conductive paste cleaned and replaced


Cleaned all fuse contacts and fuses themselves
Cleaned injector grounds and engine head ground strap connections
Cleaned body grounds behing both headlights
Cleaned coil contacts (primary side)

Backprobed CPS and saw a clean, consistent frequency change with engine speed at the most problematic engine speeds.

Disconnected AMM, car stalls when throttle opened
Disconnected TPS (error code 1-3-3 thrown)
Disconnected knock sensor (Error code 3-1-2)
Held my hand on the Fuel Pump Relay (resoldered years ago) while problems were happening - felt no clicking during the episodes.
(I have a spare fuel pump relay I will resolder and substitute tomorrow)


All of these have had no impact on the problem.
This all started the night I replaced the actual heater core, but the car had driven perfectly with the dash torn apart for over a week. I can't believe this is random coincidence.

I'll describe it again from the beginning.

Car starts and idles fine, no hiccups, slightly long cranks, but not excessive to me. Car accelerates with full power - it almost never cuts out if accelerating w/throttle ~>1/3 open.
Driving along at a steady speed, the engine will suddenly lose rpms, the tach and vacuum gauges drop, the gas pedal becomes nonresponsive, and then the car goes back to running normally after a few seconds. This is more common with city speeds (25-40), and is worst between 1500 and 1800rpm. These episodes last at most 5 seconds.

At other times, while cruising at highway speeds, there will be one or many sudden power-losses like the spark is shut off momentarily. These episodes happen either one at a time or several in a row, sometimes pulsing as though someone were flipping a switch on and off. At its worst, I'm trying to cruise along at about 1800rpm. I'm not sure why, but that's where it gets really bad/likely to happen.

I normally can't get more than a block from my house without at least one of these stumbles/stalls happening.


I pulled on all the wiring bundles under the hood and the ones I've moved under the dash (at idle) and nothing has happened.
I also checked for vacuum leaks with starting fluid and couldn't find any.



I'm at my wits' end. I've done everything I can think of and then some. There's an indie volvo guy near here, but he's a little crotchety and doesn't have formal training - but he does seem to know his volvos very well.

Please, someone, make a suggestion. Maybe the fuse or relay panel has a wire coming loose because of how it's been sitting? I moved it around and couldn't create a problem.