96 850 R rough idle / misfiring when wet

Post by **Clemens** » 27 Jan 2016, 07:06

Hi!

My 96 R has a problem with erratic idle (mainly in D and R, sometimes it feels like one cylinder misses out, otherwise it´s smooth with somewehee around 900 rpm) and misfiring at higher rpms, but only when it rains or is very humid outside.

My guess: Ignition components. The Bourgicord wires are from ´96, NGK spark plugs of unknown age / mileage from PO.
I guess I´ll go with OEM plugs and wires and a new distributor rotor for now. The ignition coil looks ok (no white stain on it or sthg.).
Or would you suggest something different first?
The IAC probably isn´t the fault cuz it also happens at high rpms.

I doubt it being a vacuum leak because it only happens when it rains.
Also, the compression is good and the PCV was done recently.
No CEL come on (but the lamp works).

Thank you,
Clemens

Post by **theWIFES_S70** » 27 Jan 2016, 08:35

Get that tune up in there. I can't imagine twenty year old wires would still be good. So many points where water could come in contact with exposed cables (especially around the boots on a twenty-year old car). I would guess that's the problem... Also, everyone here swears by the Volvo OEM plugs. You might also want to carefully clean out your Mass Airflow Sensor (just take it apart, carefully, and douse it with MAF cleaner). I'd also replace the air filter while you're at it. Good luck getting rid of that rough idle!

Post by **scot850** » 27 Jan 2016, 11:47

I agree with Marco, try the basic stuff first. Check the distributor cap and rotor. Chances are they are worn out, and the cables too. Others will tell you, you can use other brands of plugs or cables, but I stick to OE on the plugs, Bosch on the cap/rotor and Bougicord for the cables. Check while you have the distributor cap off for any oil or damp in the distributor.

Neil.

Post by **Clemens** » 27 Jan 2016, 13:30

Thanks,so I just ordered the rotor, wires and plugs through Volvo. So the wires should be Bougicord, Rotor should be Bosch. Interestingly, the dust cap of the distributor is no longer available. Probably not a huge loss.
Btw., who was the OEM manufacturer of the Volvo plugs?

Post by **benpineapple** » 27 Jan 2016, 15:12

Clemens wrote:Thanks,so I just ordered the rotor, wires and plugs through Volvo. So the wires should be Bougicord, Rotor should be Bosch. Interestingly, the dust cap of the distributor is no longer available. Probably not a huge loss.
Btw., who was the OEM manufacturer of the Volvo plugs?

Nicely done. Pretty sure Bosch is OEM (the FR7DC or 7555). I've always used NGK plugs for my cars. No complaints there.

Issue you describe is I think a combination of a loose spark gap, and a bad spark plug boot. Moisture is getting in there and making it harder for the plugs to spark. I had the identical symptoms on my 1990 240, to the point where it would have to turn over for like 10sec to start if it was raining out. Regapped them, and didn't have any issues after that (replaced them shortly after though).

Check the air filter while you're at it. If the plugs and wires are that old, who knows what other simple things might need some attention.

Post by **FLXC90** » 28 Jan 2016, 14:39

When you removed the distributor cap, how did it look inside? Normal tracking or oily and wet? Cam seals tight? Did tune up parts fix your issue?

Post by **Clemens** » 29 Jan 2016, 08:29

So, just back from the test drive. Best 280€ spent on the car so far. One tiny step closer to Stage 0.

First I was lazy and thought just do the plugs and wires. But then I luckily decided to take the dizzy off cuz I wanted to see if what I suspect as a slight RMS issue is maybe just the Cam seal (Now I know it´s not the cam seal).
Glad I did. The cap was a little dirty with a dried crust of oil fumes that had collected over the years. I cleaned the 5 posts and set it aside. THen I took of the rotor. Wow! That thing looked terrible. THen, on the other hand, it must have had at least 1 billion rpms on it in it´s lifetime, so that´s okay. I put the new rotor on, the old dustcap (which would have been 51€ at my Volvo dealer - luckily it was discontinued) and the old cap. Volvo plugs gapped to .028, new (3/2015) Bougicord wires (the kit was missing the mai wire from the coil - that sucks) and then I fired it up.

The test drive was great. It felt like another car. Like the RR version of an R kind of. I had way more low and midrange respone, it spooled up better and smoother than ever. From how it feels I wouldn´t be surprised to see a better gas mileage.

I´m sorry for the old wired though cuz I wanted to have the original wires in the car when it turns 20 this June. Well, I guess I can keep them in the trunk...

Post by **benpineapple** » 29 Jan 2016, 11:45

Clemens wrote:The test drive was great. It felt like another car. Like the RR version of an R kind of.

Nice! Super glad it's back! Your car thanks you for this new life you've given it. Hopefully no more misfire when it's raining.

Post by **Clemens** » 29 Jan 2016, 13:53

Yeah, I hope this is the car which I can finally improve over the years rather than watch it decay slowly. Thanks to the great info on this forum I think I can succeed.

Post by **abscate** » 30 Jan 2016, 05:00

Excellent. If your are near the ' Bavarian end' of Austria let me know and we can have a beer...my partner and I manufacture lasers in Gotzis..