After Removing Catalytic Converter ...

[vcp]

UPDATE: Changed the fuel filter (3rd time in a year) and finally got a chance to take it on the highway. (Had been running fine on short city jaunts up to 80km/h, although sometimes hard to start when warm.) Drove at speeds up to 100km/h on the highway and everything was fine for first 50km then started to get intermittent slight stutter under load uphill.
- Dave - Checked the vacuum advance - looks fine.
- SynthDesign - no tach so don't know idle speed
- Petros - can't find a leak but you could be right

Thinking I'll change the plugs next and see what that does.

[vcp]

FINAL SOLUTION!
When pulling the spark plug wires (yes, carefully ) to put in new plugs, the 2nd wire left about 4 inches of the actual wire (from inside the rubber tubing) attached to the plug. The wire was fried and crispy and just came apart. Assume the others weren't much better. Replaced them all with new NGK wires to go with the new NGK plugs and the next day drove 300km at up to 115km/hr with nary a stutter. Mystery is solved! (On to the next one.)

[Petros]

bad spark plug wires...I once had a bad experiance with this.

my first real "project" car, one that I fixed all up to improve performance (a '65 Volvo 122s...not exactly a performance car, but it was fun to work on). I wanted to dress the motor up after I had improved the power and performance with a major overhaul (with many tweaks). Having running good, I wanted to copy some of my high school class mates to dress up engine on my car. I bought some fancy looking "performance" spark plug wires. they were really cool shinny red translucent insulation that you could see the wire in the middle, with bright blue caps on the ends. looked kind of silly on a volvo, but I was in high school, what did I know about performance. They cost about three times more than the standard black wires, so them MUST be good. In a matter of weeks the engine started running rough at idle, I would check everything and make adjustments (this car used points, rotor and coil ignition system, which needed almost constant adjustment).

several months of this becoming progressively worse until it was only running on 3 cylinders. I did a power drop test to isolate the bad cylinder, when I pulled the #2 wire, the connector stayed on the end of the plug, and the chard remains of the melted insulation and burnt wire were hanging out, being hidden by the fancy blue cap. I than pulled the rest and cut open the other wires connectors, found two more burnt connections. I put my old wires back on and have never bought fancy "performance" wires since. I felt snookered and foolish, bought costly crap for my car to improve the looks and performance, but ended up creating a problem (it can't be the wires, they are brand new!)

It seems to me the longest lasting wires I have ever used were the factory brand wires, lasting many years, even decades.