Helping brother in law out with his 97 850 T5 (turbo) He was getting a check engine light with codes P0300, P0304 and P0305 associated with the light. These codes are for a random misfire on clinders 4 and 5. We went the whole route and changed all the plugs (OEM), plug wires, cap and rotor. Issue went away for about two months and now is back. Car runs fine and you can never feel the misfire, but the check engine light comes on. You clear the codes and about 250 miles or so later, they are back.

Ideas, suggestions? It is more of a nusiance than an issue, but still, I would like to find the cause and fix it.

Glenn

 

Check the plugs - are they correctly gapped? are they the correct temp range? For starters, I'd probably throw in some Volvo OEM plugs - particularly if you used some platinum/iridium plug. Oddly these cars prefer the old copper core plugs - they spark hotter but don't last as long. Any other symptoms? - like long cranking on cold starts etc that would suggest a rich fuel mixture (the fuel trim codes are long term codes so if you have a fuel pressure regulator issue it can show up as a misfire code and not a fuel trim code). Its also possible you have a weak coil - IPD sells a nice up-market coil that'd fit right in.

 

No, it starts right up within 1-2 seconds of turning the key, idles fine, uses no oil. I wonder if it might be a couple of dirty injectors on cyl 4 and 5......but then again, it runs great and idles smooth with no smoke.......