Hi Folks, My wife has a 1998 V90 with ~80k on it, and it has been running rough (particularly when cold), getting worse over the last 10k miles. No chk eng light or codes. Oil is 10w30, changed every 5K. It acts almost like a miss, so I finally did a compression test: 190-200PSI all around (higher than I would have guessed). I am thinking of looking at the coils next. Anyone have experiaence with this sort of problem? Would a cracked or carbon tracking coil snout trip a code? 200 PSI seems high, maybe a carbon buildup, or is this about right? Problem is not seasonal/ climate related. I also checked the color codes for the coil pack wires to make sure they were in the right holes (they were). Why didn't Volvo number them? Thanks, Tom

Hi, I know it's probably not this, but does the problem go away after a few minutes of driving? Mine did that forever, and I could never figure out what was causing the problem. And it became much worse when the weather here got cooler.

Problem: low-octane gas. We'd ben using the cheap stuff since day one. Then one day, I tanked up with the good stuff right before a road trip. I guess it cleaned the engine out, and got it used to running high octane again. i have never had the symptom since (never used the cheap stuff again, either). My guess is that the knock sensor was probably going apeshit with the cheap gas, and that's why it was running so bad.

Hi Hans, We've been using 91 Octane from Sam's Club; It's anybody's guess as to what really comes out of their pump. Maybe I'll try a tank of Chevron Premium. Thanks, Tom

Yeah, come to think of it, I had the problem a bit even when I ran 91 too. Ever since I figured it out, it's been 93 octane ever since for our car. It only costs about $4 more for a full-tank fillup. And I've found that some gas stations will do a special like 93 for the price of 91 on tuesdays if you pay cash, wear a green sweater, and hop on one foot while pumping.

If that doesn't work...

You've got 80k miles and this started 10k ago, right? did your mechanic perhaps misadjust your timing when he replaced the belt? I'm pretty sure there's a way to advance/retard your timing if you take the belt's cover off.

Hans747-betcha got it right there on the belt change over-had an indy do mine one time(never again) and the belt was 1 and a half teeth off on the exhaust side -car ran but power was down. O yeah-JBowers says down below in another post that fuel pressure running should be 40 lbs.
Poolman

If it's only running rough when you first crank her up I would say look towards the temp sensor which is below the thermostat.
Might check all the vacuum hoses that can cause one to miss and have little power. You have a healthy engine with that kind of compression. How long have the plugs been in there-you did put new ones back-right? Could be a number of things from the crank sensor getting ready to go-mass air meter-throttle body sensor-might try unhooking the mas air meter then cranking the car back up and see if anything changes-also try the same with the throttle sensor-you will have a code thrown as soon as you unhook one of the sensors, so be ready with your scanner to reset the code after you hook everything back up.
The first thing I would do is to clean the idle valve located on the air bonnet just next to the throttle body-that can make one idle funny also.
Most time when you have a cylinder misfiring there will be a code to tell which cylinder is weak. Check all the vac hoses very carfully-also check the vac tree that all the hoses hook up to on the intake-there is an o ring in there that can leak air also-but probally not as much as to cause your problem.
There are power stages that can go bad as well on the front side and back side of the intake that handle 3 cylinders each-if you can tell which cylinder is giving the problem you could switch the pwer stages and see if that moves the miss to another cyl then telling you that in effect that it's a power stage.
Good Luck
Poolman

Hi Poolman, Thanks for the replies. I will look at the vacuum hoses etc, but it doesn't feel to me like a vacuum leak (also, the climate control and brakes are working normally). I replaced the temp sensor a couple of weeks ago due to a haywire temp gauge and cooling fans, but that had no effect on the miss. I would describe the miss not as a dead miss, but more as a partial miss on more than one cylinder. The engine just isn't smooth the way a straight 6 ought to be, and it seems to be getting worse. Power also seems to be down. I am not suspecting the AMM or CAS because they would affect all 6 cylinders equally, I think. Do you have any more info on the power stages? Do you recommend dismissing the coils as possible culprets? Plugs have <20K miles on them (Bosch Cu cores) and look good. I will replace them anyway next time I have the coils out. Air filter is clean. Thanks for your thoughts. Tom

I'm not sure about the coils-me thinks that when you have a coil going south, that would send a code to the computer telling you that you have a miss in that cylinder. Do you have a scan tool to reset a code if it's thrown?
If you have a scan tool to reset everything I would try unhooking the mas while the car is off-then crank her up-if she runs ok,you'll know that the car is in limp home mode and that the mas was the culprit.
You could still have good brakes with a vacuum leak by the way-the line to the brake booster is seperate and it would only take a little vac leak to cause you to lose power. I have had this happen and not throw a code. I agree with you-don't start throwing money at new parts but check what you have then make your move. Another part that could give some problem though would be the knock sensors-might try reading up on them-there's good write up about them in the faq's.
Also on tyhe back of the fuel rail is a hookup that you can get a reading of your fuel pressure-if your fuel pump is going down it could give you the same type of power loss your experencing-just noodling along here
Poolman

I'm hoping to spend some time with the car this week. I do have an OBDII scanner, so I can try some of the disconnect tests. I have heard that the coils can be prone to cracks and/ or carbon tracking. I think the coil wouldn't tend to throw a code unless the primary winding was compromised. Any opinion on this? I guess it's just a matter of due dilligence. I will check fuel pressure and vac systems etc. Any Idea what the fuel pressure spec is? Does limp-home mode typically throw a code? Does Volvo have a computer interface that will give more info than OBDII? Thanks, Tom

My statment about individual cylinders inter facing with the computer was from a number of times this has happened with my car-the last a few weeks ago when there was a skip starting up and then a code thrown-from the #5 cylinder-popped the plug out and in went a new one and everything was fine again. My thoughts are if a coil was going down or carbon tracking and causing a skip it would give up a code for that cylinder-when you pull your plugs next time see if you come up with one that looks wet-that could be a dead give away.
Poolman

Just tought of another thing-under the air filter in the air box is a valve that works on heat and if fails will keep the car running on hot air from the engine-if thats happened it can also cook you mass air meter and cause havok.
Myself and others here have unhooked this gizmo and fixed the air box to only allow cold air in at all times and works just fine-with out the hot air valve.
Poolman