9'97 850, skip and pulsing

de-accelerating.

tach)....leading

Does it occur with cruise control on?

One problem with 850s is sticking throttles. They can stick off and then suddenly accelerate. I haven't experienced them sticking on and then suddenly decelerating.

Water in the gas is a real possibility. A can or 2 of dry gas will rule out that possibility.

Does this occur when the gas tank is at a certain level. If so it is related to the fuel pickup or intank fuel pump.

Another possibility is slime in the gas tank. This is usually caused by mixing brands of fuel. Some budget brands use additives that can combine with other brands to create this slime layer. I have seen the slime layer, but can't confirm the chemistry that caused it.

Hi,

When you say you have replaced the "wires", does that include the plastic extenders that reach the spark plugs. I had a subtle problem like yours that took at least 6 months before it got bad enough for me to diagnose properly as a "miss". I was suspecting all sorts of things. The plastic insulators break down eventually and from what I've been told this is not peculiar to only Volvos. My car had done about 90,000km. Normally these are supplied if you buy a spark plug lead kit.

Regards Barry

de-accelerating.

tach)....leading

I had this problem on my 98 S70 during light acceleration at 120 km/hr. I had the benefit of having access to a Volvo System Tester, and noticed injection duration varying from 8 to 10 ms, sagging occurring at 8 ms, running fine at 10. No lambda (check engine) light, so I guessed (correctly as it turned out) a new front oxygen sensor might cure the problem, since nothing else could really affect the mixture that much.