'87 911 Low RPM stumbling problem in the Rain

[iwhelan]

Hello, I have an 87 911 that has been running perfectly fine. Plugs, rotors, and cap are a couple of years old and wires are one year old. This Spring I haven't driven it a whole lot, but did a couple hour trip a couple weeks ago with no problem and yesterday it was fine driving about an hour to my destination.

Later in the day it was very rainy on the way home but driving in town from where I was, the car was driving fine. I got on the highway and it was driving perfectly until about 30 mins later I got off the highway and it would stumble or miss at low RPM and then maybe somewhere above 2k it would smooth out. If I kept my foot light on the throttle it was a bit less rough. We made it home but even idling was a bit rough once I made it to my driveway.

The next day everything was fine.

I'm guessing it has to do with water getting into something, and it is probably hard to diagnose, but is there something common to look for that tends to happen on these cars in the rain? Thanks.

[proporsche]

have a look inside you distributor cap

Ivan

[Targa Me]

I experienced this with my '84 3.2.
It turned out to be a small void in the air filter assembly that was allowing moisture to get in. The 3.2 doesn't run well on a fuel/air/water mixture.

[iwhelan]

Thanks for the suggestions. I will check the distributor cap and make sure it's sitting properly. If moisture is getting in during a storm, I'm not exactly sure how I'd stop that. It's all stock components.

Regarding the "small void" in the air filter assembly? Where was this void? Do you mean the filter wasn't seated properly and water was getting in past the seal?

Thanks!

[GH85Carrera]

When you pop off the distributor cap, clean any dirt of whatever, and hose it down with WD40. The WD stands for water displacement. Don't have WD40 running down the inside of the cap, just spray some in, and wipe it down any excess with a paper towel.

You might take off the crank sensors ONE AT A TIME! and put a dab of contact grease on the plastic parts, and be sure the connectors are corrosion free. Just be 100% sure you don't mix them up or the car will not run. Do the same thing for the head temp sensor connector.

Also, at night, in a dark area, start the engine and look for any sparks from the plug wires or other sources. The bright sparks will be easy to see if there are any.

[iwhelan]

Thanks Glen, I will put some WD40 inside the cap. I think I actually did that when I installed it, but it's been a couple of years now so I don't remember for sure. Probably can't hurt to do it again.

I'll check the sensor connectors too. I have never had them apart so far, but some dielectric grease surely can't hurt.

On the night it was running rough and idling poorly I did pop the engine lid and luckily I did not see any sparks.

Of course the next day the car ran perfectly so it's tough to diagnose at this point. I'll try what you suggested though.

Thanks!