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Hello!
I’ve been trying to find the solution to this problem for a while.
I have an 88 VW cabriolet, with a random intermittent miss. By random, I mean it happens on any/all of the 4 cylinders.
I did a power balance test, and all 4 cylinders seem to be contributing fairly equally, and no matter which cylinder i deactivate, the intermittent miss still happens.
It’s very intermittent when warm, but is almost guaranteed to happen when the engine is cold. Once it warms up, it’s almost totally — if not totally gone.
The exhaust smells (a friend compared it to rotten eggs) a bit, it smells like it’s burning rich, but I don’t know if that’s because the cat has long gone bad (which I’m 99 percent sure it has) and is unrelated or not.
I couldn’t find any vacuums leaks (but I would think leaks would cause a lean condition, not rich), I figured it couldn’t hurt to throw ignition components at it, so I replaced the Cap, rotor, Plugs, plug wires, and coil. No luck.
Could air be leaking in past the injectors? Could that cause a flow problem that causes a miss?
This car has an O2 sensor in the exhaust manifold, apparently these very commonly go bad causing a rich condition, but again, I can’t see that causing a miss.
Any Ideas or suggestions would be great!
Thanks.
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On a vehicle that old you also can’t rule out a mechanical issue. A couple of things.
First, the rotten egg smell is actually the fuel, not the catalytic converter. Sulfur is sometimes in fuel and when burned, it can cause that smell.
Based on the temperature differences you reported, I’d defiantly be looking for a vacuum leak. I know you say you checked, but I would advise checking again based on your description of the problem.
Lastly old single wire O2 sensors were almost a maintenance item. I don’t think you’d be off base by just replacing it as those sensors did get old and cause fuel mixture issues.
More info on solving issues like this here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Good luck and keep us posted on your progress.
Ok a bit of an update.
I realized I never mentioned it before, my car has a gasoline engine, and not a diesel, incase this is a factor.
I didn’t manage to find a vacuum leak, but a couple things that might help.
So I sprayed water around all the vacuum lines, the intake, the airflow meter, the throttle body and anywhere that there was a seal between the intake and the engine. Either I’m not noticing the difference in engine RPM, or there isn’t one. I didn’t hear any sucking or sizzling from water being sucked in, although there was one thing that I noticed:
My car has an Auxiliary Air regulator with a bimetallic strip on the back of the intake that’s supposed to heat up and close once the car has warmed up, but it always sounds like there is air whooshing past there. If I pinch off the line when it’s warm there is almost no difference, but when it’s cold, you can hear the idle drop.
This sounds normal to me since when I sprayed it, RPM didn’t change and there was no sizzling from water being sucked in. Am I wrong?Here’s the big thing that I noticed with the weather getting colder. When it’s cold outside, like below 10ºc (50ºF), the engine seems to run better at start up, higher idle, seems like it has less engine missing (but I’m not sure about this) and starting is easier.
Hot restarts aren’t a problem, but warm outside temps 21ºC (70ºF) seem to be the most troublesome. It still starts fine if you give it some gas before hand, but it’s fuel injected so I don’t think I should need to do this.
One other side note
The engine, once it’s warm, or in the summer, idles very low, it doesn’t stall, but the idle is (according to the Tach) at about 400 rpm at times. (This seems to be temperature dependant again, the colder the engine, the higher the RPM, then it kinda bottoms out at warm normal running engine, then if you get the engine really warm, like by driving down the highway for a long period of time, then the engine will idle higher a bit.)Gaahh!!! So many symptoms with so many different possible causes.
Can water be getting into the fuel system causing the misses, and the rest (burning rich, low/inconsistent RPM, hard to start at times) just be up to the bad O2 sensor?
Maybe I should just post a video of it running… that might explain more…
Yeah, I think I’ll do that and post back again.
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