Hi, I was hoping I could get some help diagnosing a problem that is very hard to reproduce in the shop. I have a 1993 manual 850 sedan with 300k.

So here's the scenario: it's a very wet and rainy morning and I'm starting the car for work from bone cold. Car starts fine, no issues yet.
Car drives fine for a couple of minutes and then at idle (e.g. stop light) starts to hiccup and stutter a little. At this point, any high load on the engine will cause extreme stuttering that will likely stall the car, that is to say, taking off from a stop at low rpms or dropping into too high a gear for the speed.
Sometimes the car will just stall on idle at a light if I don't keep my foot on the gas to keep the revs up. To keep the car going I drive it as much as possible constantly above 2k rpm, but in traffic sometimes I just can't keep it up and I'll occasionally stall all over the place.
Car sometimes has trouble restarting from a stall, but usually restarts within 10 seconds.
Once the car has been driving for 5-8ish minutes, whether the problem has appeared or not, it will be fine until the next cold and wet start. I haven't tested this extensively, but if I just start and then idle the car for that long before driving, I don't think it will happen.

The issue doesn't 'always' occur in wet conditions, but when it occurs the conditions are 'always' wet. I take the car to a specialized Volvo shop and they have already checked electrical without finding anything.

Any ideas? I'd appreciate any help.

 

You have high tension electricity "leaking out" of the ignition system. This is basically why there is a concept of bad plug wires. In other words, why wouldn't they last for eternity? It's because they do exactly what you describe.


Normally that means you want new plug wires, but you might prove me wrong and find some other issue with the high voltage part of the ignition (I doubt it). If you're curious about this, just for fun, look at it in the dark, running. Take the cover off the plugs first, I guess. This is just for fun. turn all the lights off.

 

Hmm, from everything I've read this really does seem to point to a plug wiring short. I'm pretty certain that's exactly what the shop checked last time and they found no problem, but I'll have them check again. I'll see if I can try that lights-out test.

It may be worth noting that my fuel pressure pulse damper had to be bypassed because the part has seemingly been discontinued by Volvo. I could see that potentially causing similar problems, but not being moisture dependent.

This has been going on for over 8 months and gotten more frequent.. I've just been surviving because of the dry Canadian winter. Now that spring has arrived, I really need to get it resolved.

 

I would suggest that you change the plugs, plug wires, distributor cap and rotor. I would be willing to bet your issue will go away.

 

Personally I am not believing the shop tested your plug wires. it's probably possible to test them, but brand new ones are too cheap to make it worthwhile.

 

firebirdparts, agreed. I think they just inspected them for obvious cracks and didn't find any. They weren't able to reproduce my problem, so I guess they assumed I was crazy. Bit disappointed in the usually great shop.

Anyway, I'm going to replace the wires and probably the cap and rotor too.

Thanks for the help.

 

the easy way to test your plug wires is to remove the cover and start the car in a dark garage - quite often you can see the arcs. if not at first, then try misting the wires... with that said, firebirdparts is spot on. replace the wires/cap/rotor is the easy solution (particularly since you can match the wire the new cap - Bosch was kind enough to put the firing order right on the cap. (all you need to know is #1 is the farthest away!)