1999 XC70 Engine running on 4 cylinders

[Dynamic D]

Finally today I had some time to look back into the car problem. Unfortunately the car now runs fine. It has been sitting in the garage (unheated) for a week and a half and now suddenly, I try to start it and everything is fine. I imagine that I will have to wait that the cylinder #3 stops working again to find out what the problem is. This is really anoying because I cannot use it in the meantime because it is unreliable (I have kids, so getting stuck somewhere with this cold is not an option).

Anybody have an idea of what I could look for in the meantime ?

Oh, by the way, the coils are Beru and the spark plugs are NGK and the one I swapped the other day is a Volvo.

[Dynamic D]

Ok, so the car worked a few days. Then suddenly again the engine vibrate and the car is in limp mode. I left it running for a while (near 40 minutes) and then suddenly it works like new.

I used it for small displacement near home for a few days without problems and this morning something new occured. The engine was warm, everything was working ok. I was waiting at a red light and when it turned green, the engine had no power.. like when the car is in limp mode. Turn around, get back home (5 min drive) and still very little power. I had the impression that it produced a lot of smoke though.. When I got home, I stopped the engine, waited a few minutes (the time to get my scanGauge) and tried to start it back: it worked, but with the rough engine again.

Another detail, the ScanGaugeII that I have tells me "no code found" with in addition with the "not ready" message. After looking at the user manual, it says that the cause of this is "The vehicle has not completed its readiness Tests since the last time it was cleared or the battery was disconnected." The last time battery was disconnected is at least 1.5 month and code cleared is 1 month... does it take that long to complete the readiness test ?

My impression (and I'm no way near an expert) is that the problem is purely electrical, but I don't have a clue on what cable / connection could produce this. Just for the fun of it, I've tried to find the engine harness on the Volvo web parts, but it is near 1000$, a little too expensive for a shot in the dark...

As for the cheking the injector, I wanted to wait that the problem come again, but now that the car went into limp mode with the engine running smooth, I think it's not worth it anymore. Or is it ?

Any ideas how to debug this ?

Thanks !

[Dynamic D]

I just went outside to confirm that I still have no codes (and still no codes), but I noticed something: At idle, the engine vibrates a lot, but if I maintain the trottle to let say 1800 RPM it is smooth. As soon as I let the RPM lower a bit, it is rough again (ex 1800 to 1500 or 2000 to 1800 RPM). I don't know if this information can help..

[Pauloil]

you need to go to oreilly's and get a compression tester and test compression. one of your cylinder may have 0 pressure

[rspi]

I would run a compression test while it is running rough. If you have a valve sticking a compression test will tell you.

[chuffs]

That model can be: the vacuum system issues, check ETM; butterfly,relay or wiring OR electrical SYSTEM drops due to battery/alternator/corroded lug/wiring from battery to eng. compartment fuse box. A few good Youtubes on issues. call XeModex (Google them) also for ideas. Good luck.