Got car washed - misfiring and RPM hunting at idle only

Deleted - think bad spark plug tubes are finally catching up and causing a bad vacuum leak at idle. Will replace and report back. Car wash prob just a coincidence.

Cracked coils getting wet. Once they dry will probably run fine. jmo

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thanks allcool. just gonna buy coils/plugs/tubes and hope it fixes the issue. Had to've been the pressure washer, combined with the fact that I saw him start it and back it up a few feet, then turn it off again mid-wash. Not sure why he did that. Maybe he shorted something? Just hoping this isn't a bigger issue than it is. It's really running like sh*t at idle. No way new Beru coils went bad in just 30k miles.

I rebuilt the engine in my neighbor's 996 and gave it back to him running well. His well-meaning young son washed and detailed the exterior. After, the neighbor brought the car back because it was misfiring. So, I asked him "Did you wash the car?" he said yes. We got in, drove the **** out of the car until the water soaked air filter dried out and it ran well again. Lesson: never wash your Porsche 996/997 with a garden hose dousing water over the engine lid. In your case, you should replace what ever ignition components that are older than 30,000 miles. AND never wash your car again. Use drywash.

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I wonder if water did get sucked up through the intake� doubt it though?? Or maybe it fouled the maf? I�m not getting any maf error codes and the car�s idle changes a bit when I disconnect it but doesn�t run better or worse. Air filter looked dry yesterday.

More likely a cracked coil as noted above unless he just went crazy filling the engine compartment with water. The no wash advice would seemingly imply never leave the car in the rain too. Clearly you can. I cover the motor with a towel washing, carefully avoiding the latch mechanism (in fact I just leave it unlatched), and of course removing before starting the car. More to prevent hard water spots everywhere than anything else.

He definitely went crazy with the power washer, especially on the rear wheels and rear wheel wells. If you look at our cars, you can 100% spray water directly onto the coil connections on both banks. I watched him do it and he started the car mid-wash to back it up a few feet. I thought nothing of it. Probably cracked coils, just can't believe it given they're only ~30K miles old (so are the plugs). That makes me think something else is bad. I'm throwing a bunch of codes for misfires and the O2 sensors detecting a lean state, so the car's running rich. No misfiring through the powerband, only at idle. It does feel like it goes into some sort of limp mode from time to time, sometimes it actually feels pretty torquey - more than usual. I have a cart loaded with FCP with new spark plug tubes, plugs and coils. I replaced the MAF 30k ago too. Only other possible culprit is the ICV so may just get another used one from DC Auto for peace of mind. Bad ICV wouldn't cause this poor of an idle though.... or would it? If it is just a $60 fix and I can replace the ICV, I'd much rather do that than unnecessarily swapping the coils and plugs. The wash/detail was also $220 so still struggling to pull trigger on parts that I wouldn't have had to replace otherwise lol. On my way there the thought of "I should just wash it myself" crossed my mind too. Car was running awesome before the wash and had no codes. Actually drove it from Philly to LA last March. Fun trip. Thinking next steps are to pull the coils / inspect and re-seat the coil connections. I won't know if the MAF or O2's are actually bad unless I use a computer, so trying to get my hands on an Autel or someone with a Dura. I'm in Hermosa Beach, CA if anyone could lend a hand.......

FWIW, I have 62k on my 02 and over the past 21 years have replaced my coils 3x already. One will eventually show a misfire so I replace them all and the plugs. I have replaced my MAF once or twice as well. Eventually they go bad, crack, etc. Same can be said for fuel injectors. Just happens. High pressure water probably doesn't help.

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Strange its still misfiring if its from water fouling cracked coils. Usually by the next day and a hot engine, they dry up and all is fine again. Unless a hot coil got a cold blast of water and cracked badly never to work right again.? Well, if you know what cylinder(s) are misfiring, and have your old coil packs(and they're old but working), swap out the offending coil(s) and see if that changes things... Just a thought... I wouldn't throw a bunch of parts at it, better to figure out whats wrong and fix it. jmo

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Yeah believe me I don't want to start throwing parts / $ at it either. I already paid the $220 to get it washed haha.... Barely held an idle today and it's running very rich... idle goes up and down. could a power washer ruin the connectors to the coils themselves? Electrical problem now? Idk. Or water got sucked up and the MAF is toast? Doesn't run much different with MAF disconnected and don't think a bad maf would cause it to idle like sh*t unless I'm wrong.

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Ya, wouldn't keep running it like that. The imbalance could cause undo wear and tear on reciprocating parts. Start with taking out the coil packs, do you still have the old ones..? do you know what cyl is misfiring, if so start there...? Is the air filter wet..? Hmmm, idk, after rereading this thread, and it being more than enough time for things to dry out now if it was a water problem, maybe sideline the coils for now and do a simple check for vacuum leaks. I've seen aggressive pressure engine cleaning blow apart old vacuum lines, etc... Worth checking out first maybe,, if you can't get any codes to go by.

Pulled a bunch of stuff tonight - all bank 1 coils and plugs. The coils look brand new. The plugs look fine and are oil-free, even the one that I thought was leaking through the spark plug tube. So now I'm thinking there's nothing wrong with the coils, plugs, or tubes. I wonder if it is as simple as my ICV. I bought a used ICV from DC Auto ~30K ago (mileage unknown). I changed the MAF with a brand new Bosch unit ~30K ago as well. Might change those two first. Only other thing I noticed is the TB was sort of dirty (but I highly doubt that would cause the stumbling (sometimes stalling...) idle), and the intake plenum had a bit of oil in it. If I looked inside bank 2's intake plenum, I could see a small pool of oil. I think that's normal though.

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Sounds like your AOS is failing. Oil in the plenum is not normal. Check with Porschetech 3 he will fix you up with the UAOS kit for your car.

The other possibility is a fractured or dislodged vacuum line. Does the car throw codes?

When the AOS diaphragm ruptures that�s a big �ol� vacuum leak as well. I wouldn�t drive the car until AOS is inspected or replaced .

Went to pull bank 2 coils and plugs today. Got to cyl 6 (I believe that's the one closest to rear) and the damn connector wasn't clipped in. Came right off when I pulled up on the boot. Strange still that the car wasn't missing through the RPM range though, only at idle... Wonder if the guy's power washer undid the connector ever so slightly? Thinking of how you push directly onto the clip and it sort of pops, the way a pressure washer would've undid it. He was doing the wheels too, so bet he was using the most aggressive attachment/setting (I've only used a p-washer once, don't really know how they work).... They specifically ask if you want the inside of the wheels cleaned out too. That's not getting done without a lot of water pressure (they don't handwash the inside of the wheel, nor do they take the wheel off). That said, I ordered an AOS, 6 spark plugs (the coils really do look brand new - I replaced them myself 30K ago - would like to save $250 if I can), another used ICV, and a few other misc things this morning. How difficult is it to do the AOS now that I have both intake plenums off? Bank 1's intake manifold is still on, but have been told you can swap the AOS without removing the manifold..... In total I'm already in for around $315 between parts and tools. Might be nice to just have the AOS and wait until it really fails (I'm really tired between work and this and my hands are sore as h3ll). That, and I'm by myself. I think I can manage with the tools I have but it'll be hairy I'm sure... Thanks all for the help thus far.

I can't imagine power washing wheels. Not a good idea as you are finding out. I use soap and water and a rag to wash them by hand.. Getting the inside may be hard and wheel removal may be required, but it is by far the best way and you can wash the calipers, too. To reduce the dust from the pads I recommend Hawk street pads. They have several versions and produce virtually zero dust (and good stopping characteristics). I can clean my wheels in a few minutes with a rag and Quick Detailer. Some people get their wheels ceramic coated. That may be better, but with the Hawk pads, keeping my wheels clean is a simple processes. Next, I need to swap out the OEM pads on my wife's Macan. Dirty bastards!

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You're not going about troubleshooting your problem in the most economical and time efficient way. You actually could introduce more problems to confuse the matter by what you're contemplating doing. Trying to fix your problem engine misfire by tearing down the plenums/intake, changing all the plugs and coils, aos, without even a fault code to go by, or at the least a vacuum leak test, or a manometer test on the aos, is counter productive imo. Would have been nice to just clip back on the coil wire you found lose/disconnected(?) and see if that fixes your problem before tearing apart everything you did. I'm not a expert Porsche mechanic/tech by any means, I learn a ton here, but am an expert old troubleshooter by profession and an M E. What I''m trying to covey to you is use a logical step by step process of elimination to troubleshoot your problem. Not a gun ho tear it apart and throw parts at it hoping that fixes it without ever knowing what the problem was. Always do 1 thing at a time, then test what you did, as to not confuse the problem or add additional problems unintentionally. like what you're going to do installing a used dismantler icv part with unknown working condition, or even knowing if yours is bad to begin with. For the cost of your new set of plugs you could have bought a inexpensive amazon manometer to test the aos. it would test the aos quickly and accurately. Then you'd know for sure the condition of the aos. If its good no need to change it. Occasionally others have installed a new aos that were defective from the get go. You should monitor you aos regularly anyhow and a 996 needed tool is a manometer imo. If I can instill 1 thing on you, its to not troubleshoot by being a parts changer. Use a logical step by step process of elimination. That doesn't mean installing a load of unneeded different parts till your problem is fixed, if it even ever does get fixed like that. Spend your money on the correct test tools you really need, like a code reader and manometer. Don't have to get the expensive Porsche scanner system. A more generic less expensive tool will do for many/most of the common things you'll need. I've got a $150 Foxwell that works ok for many things although its not the perfect tool for a 996.2. Ya, you could get an expensive Durametric or piwis and have the best, but it will cost ya. There are many other lots less expensive that will work for things like you need now... Don't take this the wrong way, just some simple advice that imo will help you understand and fix your car the least expensive and quickest way, take it or leave it... JMO

In regards to AOS: How far along am I now that I have both intake plenums off? Anyone have success doing it with bank 1 intake manifold still on the car? Took a look at it last night - aside from that little electrical connector next to it (looking underneath car) and the hose with the press-clamp (circle clamp - not sure what to call it), it looks pretty easy. The two 10-mm seem easy to get to, too. Getting the hoses back on may be a pain but idk. At this point I think I�m going to put the new plugs in on Friday. Re-use the coils and ensure the connectors are clipped. Clean the TB, MAF, ICV and intakes very, very thoroughly. Clean the plenums and boots. Will be spotless. Then I�m going to change the oil and drive the car hard. Spoke to a nearby tech and he said oil in plenums and manifolds is normal and more than likely indicative of not driving the car hard enough, or not taking it through full heat cycles when first started each day. He has changed AOS�s on these cars before and still sees oil get accumulated in the manifolds, mostly because the owner doesn�t take it from dead cold to operating temp, or they don�t drive it like it should be driven. If it still idles like sh*t I�ll change the AOS. Will keep ya�ll updated.

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Hey sorry man saw this after I made that above comment, wasn�t trying to ignore you. you�re absolutely right. It just so happened to be an odd set of circumstances. I *did* forcefully push down on the boots of each coil, I just didn�t pull the boot up and actually check the connectors themselves. Stupid mistake but hey, I have time and if anything I got a good look at everything through this process. Car�s actually pretty clean and hoping it will run better when everything�s together. I don�t have a problem doing all of this, putting it back together and having it still not run right, because then it�s certainly the AOS. I figure I�ll know right away / that day so no serious damage will be done. She�s not smoking or anything either so AOS (if bad) still has a little life left I think. :thumbs up: Edit- and then if AOS is changed and still not running right, will just do the ICV and MAF. That should be the end-all. If not, will change the coils as a last resort. edit x2- and Yep I did get codes. Misfires on 5 cyls and enrichment limit from two O2s.

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If you are going to change the AOS you are better off going to a UAOS w/ track drain. Among many other advantages, it has better drainage so the oil doesn't accumulate in places yiu don't want. Not to mention you won't have to replace it again, it mitigates the risk of intermix, hydralock, etc. Factory AOS is a weak link on many fronts.

I agree with allcool. The shotgun approach isn't the best way (time and money) to fix the problem. You need to understand the problem first. Has the car produced any codes? I asked this some posts ago and these codes are pointers to where to start looking. Share the codes with us.

Yeah my bad...typing too much. Posted codes in an edit on post #20. "edit x2- and Yep I did get codes. Misfires on 5 cyls and enrichment limit from two O2s." Imo the problem could be anything from bad coils, bad plugs, bad ICV, dirty TB, or bad AOS. I took both plenums off and checked vac lines - nothing. wiped down the plenums and manifolds of the tiny bit of oil they did have. Have been told it's normal (saw a post earlier saying it wasn't). I don't have my Autel anymore otherwise could rule out bad MAF or bad O2's (doubt it, just changed them a year ago). I actually think the loose connection on cyl 6's coil (rearmost, bank 2 - technically either cyl 6 or 4 can't remember) might've been it. Imo my approach has been pretty solid thus far and got a few new tools out of it that I'll use in the future...... cheers.

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Do the codes say misfiring on 5 cylinders or cylinder #5 is misfiring?

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misfiring on every cylinder except for cyl 2, bank 1. Time to do coils too then? Thought one disconnected coil would cause other misfires as well.

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No. Coils are independent. Something else is causing this. I don't know enough about these engines (mine is different than yours), but the root cause is likely something that impacts both banks and all cylinders (despite one not throwing the code). In some cases, oil residue in the intake could be a vacuum issue or a problem with venting crankcase pressure. Someone with more familiarity with your engine needs to step in. Also, keep in mind that the more detailed information you can share the better it helps us help you.

Thanks for the help regardless. Put everything back together today and the idle has improved, but it's still missing ever so slightly (only at idle). Still smells like it's running rich. I ordered 6 new coil packs, a MAF and spark plug tubes. No smoke from exhaust and can still easily remove oil cap so ruling out AOS for now. I replaced the spark plugs today and cleaned everything out (intake plenums, TB, Maf and ICV). New waterpump/coolant flush too but that's beside the point. Imo has to be coil packs? Pretty crazy - had to've been from the guy's pressure washer. Got 1-day shipping on them so will update will good news (hopefully) soon. This has been really annoying and still hate that I spent $220 on that wash.... edit- and price not really an issue here because these are parts I've bought thru FCP before and will just send the current ones in for a full "refund" / credit (their guarantee policy is awesome)

When I had a dead injector on my Turbo is showed misfires on every cylinder *except* the one with the dead injector. Easy to check. Start with engine cold. Run the engine for a minute then touch each exhaust runner.

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What am I looking for by touching the exhaust runner?

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interesting,thanks for that insight .

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Heat, showing that its firing. Cold means not working, a bad injector(or whatever)won't give enough fuel to let it ignite. don't have to run it long, don't burn ur hand...