Chuck Z

Perhaps someone here can make a suggestion(s) of where to start with an issue that has come up with my 968. It started just before I picked it up from the paint shop and has persisted since. I'm speculating that because it was started and shut down many times to move the car while it was there has caused whatever the issue might be.

I thought perhaps if I drove it for a while and got it up to operating temp it might settle and everything would be fine. Well, not so much..... At startup idle was rough (would smooth out at rpms above 2k then back to rough idle), backed it out of the garage and the driveway. Car running really rough as I leave the hood. After it heated up, the issue persisted. As long as I kept the revs up, it ran okay. Once I would shift into a higher gear and revs dropped it would again be really rough...

Any thoughts would be greatly appreciated.

Paul Waterloo

It sounds like it is misfiring at low RPM's, or this could be a potential cause. I would pull all the plugs and inspect them and check all the wires and caps.

RajDatta

Agreed, ignition or fuel related as 1st step.

Chuck Z

Thanks guys! I'll pull the plugs tomorrow and have a look at them. I check coil and plug connections and the seemed fine and no corrosion.

Chuck Z

May be on to something here guys.... Pulled the plug wires and this is what I found:

None of the connections looked compromised by rust in spite of what the area around the plug looks like. Any thoughts about how to get the rust off (before I pull the plugs)?









What it should look like...

RajDatta

That's from water making it's way past the wire seals. Looks like it sat with water in the galleys for sometime.
A new set of plugs would be a cheap and easy start.

Chuck Z

Agreed. Must have happened when I washed the engine bay.... Learned something here! Blow out the sparkplug galleys after engine wash (doesn't happen often, once it's clean it's easier to keep clean).

Paul Waterloo

That's really interesting and agree that you just need to replace the plugs.

My wife's Audi Q5 with 77K miles on the engine (with the original plugs) misfired recently and the ECU would shut the cylinder down. When I pulled the plugs, I found one that had a lot of corrosion on it, probably similar to what you will find. Once I changed that bank, I started the car back up and the misfire is gone for good.

You can see the bottom right plug with the corrosion on it, be careful, it took significantly more torque to get it out as compared to the other 5.



Comparison of the bad one and another one:



And I just replaced the plugs on my 996 for the first time last weekend, it has 47K miles. I had an issue with a coil pack a year or so go and had misfires....replacing the coil pack solved the issue, but never replaced the plugs.

So when I pulled them, this is what I found. See the top right plug has the corrosion on it...that was the misfiring cylinder, basically the same type of corrosion that the Q5 had:



Here are some close ups next to a new plug:





This now makes sense to me. If it's not firing correctly, the voltage is being shunted to ground by some other path, and it appears it is using the threaded area of the plug for a ground path that is not normal, hence the corrosion.

I'll bet you $10 that new plugs will solve your issue. Let us know!

Chuck Z

Thanks Paul, my plan is to put some rust dissolver (environmentally friendly and very gentle and non corrosive), leave it sit for a while to work, suck it out with a shop vac, blow compressed air to dry it then remove the plug.... Wish me luck!

968gene

Except for the potential for arching, having the body of the plug rusty is not a performance issue, just an indication of what the issue might be. I'd replace the wires and plugs. Water may have wicked up the wire and caused the wire to corrode. Use dielectric grease on the connections upon installation of the plugs.

Jay Wellwood

Good idea Gene. Might also consider a thread lubricant to protect the threads from future potential corrosion.

Chuck Z

Thanks Gene and Jay.

Thought about hopefully rust not penetrating below the seal or I'd probably have a much larger problem. Will use dielectric grease on connections after I clean the with Deoxit.

Pulled the non rusted plug and doesn't appear to have any anti-seize on the threads, will also do this too.

thomasmryan

Start the motor in a pitch black environment and you may find what's arcing. The 2k ohm plug ends unscrew from the wires if you want to make them easier to manage.

The VOCs in the paint shop could also foul the MAF as fumes would go right through the air filter. The MAF does a burn off controlled through the ECU anytime the car is shut off. It is recommended to wait for this cycle to complete before attempting a restart.

Chuck Z

Thanks Thomas. Upon further inspection, it looks like there is corrosion in the ends of the plug wires. May try to clean them but, probably just replace them.

I did get the car up to operating temp the other day and haven't restarted since.

Will replace plugs and clean wires and see what I get. Ultimately I'm probably just going to change the wires anyway especially if it runs better when done with the initial clean/plugs.

Chuck Z

Upon closer inspection, the spark plug wires are quite corroded. Even the spark plug hole that had no rust is probably the worst. Spark plug wires ordered....