I've been trying to track down this problem for a long time. Although it has become worse in the last month or so. Whenever I accelerate from a dead stop, the car bucks and sputters. If I accelerate more, it bogs and sometimes backfires through the intake. However, if I let off the gas, then back again it will surge back to life.

Here recently I've tried checking the AMM and the O2 sensor. The AMM seemed to test fine with the steps in the Haynes manual. And the resistance between pins 2 & 6 was at 503. The O2 sensor would not pulse between .1 & .9 volts. It would climb to .9 when warming up, but never change, even when reving at higher rpms. The heating element tested fine.

I did some searching here on the Brickboard and found how to adjust the AMM. I bought the AMM when this problem arose two months ago. Since mine is a rebuilt unit, I've heard that they can be problematic. So I found that at pin 1, I should see 1.5V at idle. So I set the pot on the AMM to 1.5V and now read around 390 Ohms at pins 2 & 6.

The O2 sensor would still not change voltage, so I also tried another trick from the Brickboard. It described that if you ground out the O2 green wire, the motor will go into full rich mode. And that if you add battery voltage to the wire, the motor will go into lean mode. Both of these tests worked. So I thought I would go and buy a new O2 sensor.

I ended up paying $150 for a new Bosch one, here in Houston. Now, with the new O2 sensor plugged in, the car will stumble and knock with any throttle movement. It doesn't buck at all with the O2 sensor unplugged.

In the last few months I've replaced just about everything...the Volvo is really testing my limits.
I have replaced:
Ignition control unit (used)
Knock sensor
Engine temp sensor (replaced when doing intake gasket)
Hall sensor (used distributor)
Fuel pump relay
TPS (clicks when moving)
AMM (rebuilt)
Main fuel pump (new fuel filter as well)
In-tank fuel pump (new sock, and white hose was okay)
Ignition coil

I think thats it, other than the basic tune up stuff. I could really use some advice on what else to try. I really don't want to give up on this Volvo because the mileage is so low. I bought it from a Grandma, with only 47000 miles!

Jack H
'87 240 DL
'92 300ZX