1998 S70 Misfiring and Stuttering/Vibrating

styoung94 · Post by **styoung94** » 02 Feb 2015, 13:27

Hey Guys.

Last Friday evening I was coming home from a hour long drive and as I was three miles from my place my S70 started misfiring. The check engine light started flashing and would periodically turn off for a minute but then return flashing again. While this was happening the car was vibrating and stuttering as I accelerated.

I checked the oil, there are no leak spots and the level is fine. There is no smoke or unusual noise aside from the misfiring. The MAF sensor it newish, 5 months old. I replaced the spark plugs today and there is some improvement. The old plugs didn't look fouled or anything, just worn. I am unsure when they were last replaced. The check engine light has not returned, but there is still some hesitation and a vibration, especially at lower rpms.

The CEL is normally on by the way. There is (possible was as I replaced a cracked elbow today) a leak in the vacuum lines. Its the typical p0172 code. I did reset the codes today when I replaced the spark plugs.

Any ideas? I'm thinking it needs new spark plug wires and a distributor cap. Any input would be great.

Edit: Its the non-turbo too.

Post by **shaker_chi** » 02 Feb 2015, 15:23

I had the same issue as you. I would start with your plugs and wires. Take them off and inspect them very carefully. If they are original replace them with O/E or 8mm from IPD. Since the CEL light was flashing you have a misfire on more than 1 cylinder. Scan your codes so you can pinpoint which ones.
Good luck.

Post by **rspi** » 03 Feb 2015, 02:23

If you have been driving around with a bad fuel mix, running lean or rich, you probably burnt a valve.

Post by **stephansvolvo** » 03 Feb 2015, 05:31

I'm in the same boat and ends up I have a few valve issues. I'm about to start that project in a couple weeks.
Start with wires, cap and rotor. If it doesnt change, as RSPI says, does it have compression? All the searching in this forum I found it seems common or at least more common that these valves will burn. I had a highway run at 110 mph and other guys said it was a steady driving speed and they ended up burning a valve.
Anyway.... Wires, cap and rotor since you got plugs in there already.

Post by **E Showell** » 03 Feb 2015, 05:39

Will these cars even do 110 mph?

Post by **rspi** » 03 Feb 2015, 06:05

^^^ lol.

It will take a while to get there but yes it will.

Post by **erikv11** » 03 Feb 2015, 08:13

With a burnt valve the CEL will not go away, it will come on and stay on due to one cylinder not firing at all.

If this came on all of a sudden then the first thing I would do is check the rear cam seal under the distributor cap, it may have blown out and sprayed oil under the cap. Far more common than a burnt valve although they are more common these days.

Th p0172 you want to take care of, how about the vacuum elbow on the end of the intake manifold?

styoung94 · Post by **styoung94** » 03 Feb 2015, 12:47

If this came on all of a sudden then the first thing I would do is check the rear cam seal under the distributor cap, it may have blown out and sprayed oil under the cap. Far more common than a burnt valve although they are more common these days.

I'll check this today or tomorrow to see what it looks like. But I haven't noticed any oil pools under the car or in any odd locations in the engine bay.

Th p0172 you want to take care of, how about the vacuum elbow on the end of the intake manifold?

I haven't messed with the code much, but I know to take a look a look at that elbow. I'll check to see what condition it is in.

If it doesnt change, as RSPI says, does it have compression?

I have never checked the compression. I would assume that it does since it isn't constantly misfiring, but I'm not sure. If I can get a tool I'll try to check it out. I think Advance will loan them out.

I'll take a closer look at the points I listed above. After I go through those I'll probably order an new cap/rotor and wires and go from there. Any chance that sketchy gas could be the culprit? I last filled up awhile ago at a Sheetz but I thought their gas is normally pretty good. Thanks for the input.

Post by **erikv11** » 03 Feb 2015, 13:24

Bad gas is definitely a valid idea, I always forget about that one but during the winter it is more common, too.

The compression test is prompted by the burnt valve theory. Never a bad idea to check compression but if the car is sometimes running smoothly at idle, then it doesn't have a burnt valve.

Post by **stephansvolvo** » 04 Feb 2015, 22:26

It gets there pretty quick. It no corvette but, when the boost kicks in it goes and the car still handles like a dream. I have learned the hard way that I should be nicer to my Volvo!