I take it that he doesn't have a plug wrench either. Because it appears to smooth out above 35mph, it may not be the plugs but they need replacing anyway. I prefer Champions myself, the plug is in the back of the owner's manual as a replacement suggestion.

Ignore the 5xx numbers, your cat converter will be just fine.

If he has a torx driver, have your son take off the engine cover so that he can see the wires and plugs. They might have not been seated correctly if they were pulled off during the timing belt change. Then, when it is dark, look for arcing.

If the engine smooths out on the highway, it will be safe to drive home. It's only 2 hours. Also have him check the water temp when the engine is warmed up to verify the ECT sensor is working properly.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

All of those codes are misfire codes. Bad Gas? If not it could be an issue with the distributor cap arcing over.

I had a bunch of those codes after a tuneup but I used the wrong plugs. Never, ever, use Bosch Platinum 2 plugs in these cars. The gap is completely wrong and it really can't be adjusted.

Bosch Copper FR7DC plugs have worked great for me and they are around $1.00 each at NAPA.

My bet is that a new cap (Bosch), Rotor (Bosch), Plugs (Bosch FR7DC gapped to 0.028), and Wires (NOT Bosch - Use the Bougicord wires) and it will run like a top. Other than that look under the hood at night for sparking around the coil - it could be going bad.

...Lee