I have been trouble shooting a problem on my '85 760 Turbo that has left me confused ever since it left me stranded miles from home.

The symptoms are:

1. Idle is low 500-700 RMP and not very stable. Car idles fine after throttle is pressed for a little while then will intermittently idle rough and low again.

2. Car will run for 10-15 minutes, then after shut off will not start again - engine sometime fires but barley ignites fuel and is similar to a car running out of gas. One can smell a gassy smell during this time. Engine might catch and then run with idle problem then cut out.

3. Sparkplugs show a rich running engine

What I have done:

1. Diagnosed Coolant Temp Sensor and it gives the correct reading.
2. Wire Harness has been patched up where required (have original wiring) but testing various engine sensors from the ECU (using volvo manual) says wirng is not an issue.
3. Distributor Cap removed and small black marks on points cleaned off
4. Oxygen Sensor diagnosed for voltage output .5 V is reading so I am assuming it is fine. CO was not tested.
5. Throttle body was cleaned.
6. Timing was checked and seems to be at 12 degrees on idling. When throttle is activated timing jumps to 20-30 degrees and maintains itself - timing change seems smooth but don't have enough experience to tell the difference if it was not smooth.
7. Fuel pumps are running
8. Fuel pressure regulator was replaced.
9. Injectors were diagnosed by sound and are all clicking away.

What I would like to know:

1. How does one test spark strength? How is the Coil diagnosed?
2. How is the distributor / cap diagnosed and when does this need to be replaced?
3. Can the fuel pump relay display intermittent problems that cut will reduce gas flow to the engine then return?
4. Any other tests I should do?


Thanks for any advice you guys my have and for reading this long post!