I have a 2001 Volvo S40 Turbo Automatic transmission about 120k miles

The vehicle is just running rough all the time. I swear it sounds and feels like it's an old Inline 6 Jeep. It doesn't sound like exhaust to me though. The engine sounds like it is running louder than it should, the car vibrates pretty hard, and sometimes it feels like it is missing/skipping when at an idle or coming into a stop. It DOES NOT STALL and if memory serves me right, it has never stalled out. Outside tempuratue seems to have no effect on it. It's not for just a little bit after starting or when idling, it is literally ALL the time the car is just rough running. Wondering if anyone has any suggestions.

I have replaced the Fuel Pressure Regulator a little while back along with plugs and wires. I use premium gas, but I have tried filling it with regular a time or two, didn't make any difference. Thought about replacing the fuel filter, but it just doesn't seem to me like it is having an issue getting fuel.

The service engine soon light came on recently, but it doesn't seem to have any relation to the rough running. From my understanding the check engine light is seperate from the service engine soon light and it is not on either, nor has it come on or flashed or anything.

I had some issues back when I changed the spark plugs; it was throwing check engine codes about missing on some cylinders. I eventually just switched to the cheaper copper plugs and that seemed to fix that issue.

I am thinking about running a gas valve cleaner type solution to see if that helps. Please tell me if that is a bad idea for this car. I know some cars don't take well to the gas additive cleaner solutions.

Other than that I have searched hopelessly through the forums and just can't find anything specific enough. I doubt it's a dirty throttle body or MAF sensor. I was thinking possibly engine mounts might be toast, but maybe for the vibrating, not so sure it would cause the loud rough running.

Anyways, any ideas or questions - let me know!

 

Sounds like it's time to change the coils. Mine ohm'd just fine and still had a misfire until I changed both of them. And if you have worn motor mounts it makes a misfire seem worse than it is. I've replaced all 4 so far.

I'd really consider better plugs for a turbo engine. Some nice Volvo OEM plugs or NGK Iridiums. Just make sure you gap them correctly. Turbo engines like a smaller spark plug gap, 028".

That "magic-in-a-bottle" stuff has never worked for me. I've bought my share too. Just never worked. You'd think I would learn.

 

Thanks Hudini !

I didn't think about changing the coils. It isn't running sluggish at all as far as I can tell, but coils aren't too expensive and I can easily replace those myself. Plus it does sound to me like it is missing sometimes. Is sluggishness always a symptom of bad coils?

I started out with double platinum NGKs and then I ran into serious misfire issues. From what I read online a lot of people recommended copper plugs for Volvos. I believe I put in single platinums (because the guy at autozone refused to sell me coppers) and the gist of misfire issues seemed to go away.

I'll probably try a bottle of the fuel system cleaner stuff, but I highly doubt it will solve my issue.

 

There are areas where sluggishness may be a problem. One is poor quality gas causing knock which retards the timing a bunch. The result is a car not making as much power as it should. The fix is premium fuel.

You could also have a slow TCV causing the boost to come on too slow. A failed TCV will set a code but a slow one? Not sure.

That's all that pops in my head at the moment.