help running rough

hi my 2001 996 this morning would not start, i had to put jump leads on and it started straight away but it is not running on all cylinders, its rough , no smoke but now the emission control light has come on, i dont get it, it ran fine last wk end i know we have had a lot of rain, any ideas, one thing i can say is that when engine is running and i remove the oil cap the engine suddenly revs higher ??? help please thanks neil.

If you take it to a good indy then can plug their computer thingy in and diagnose the problem immediately. You mention rough running following rain - sounds a lot like coil packs to me. There is one coil pack per cylinder and they do the job of an old fashioned distributor I believe. Anyway, they tend to crack over time due to heat and water. Mine did, and were replaced under warranty. My symptoms were just like yours. I found a short term cure was to give it some beans, seemed to clear out water and dry things out nicely. No idea about the oil filler cap I'm afraid.

Does sound like coil packs to me too... If engine check light is flashing don't worry too much, if it stays on, switch off IMMEDIATELY and call a garage! Have never tried removing filler cap with engine running so have no idea about that...

hi thanks for that, first time its done it, werent sure if i have messed something up by not jump starting it right, i used the battery terminals!! :what: the light it is staying on now but ive just started it cold, it started great and whilst its cold it runs great??? but light is permanently on

maybe it dried out or it is ok when its cold as it runs as choke or cold start is on. maybe its knackered?? any more help would be greatly appreciated, thankyou

Get the car checked out. Do you have AA cover? The emission light is probably on due to the misfire. I'd agree with the comments above, the coilpacks will be the first port of call, especially with current weather conditions. Oil cap removal changing revs is normal due to the change in vacuum pressure. I'd get a breakdown man out to check it over. If it is coilpacks they will diagnose it easily enough. I'd avoid using the car in the meantime, just in case.

ah super, we have had a lot of rain the last few days maybe thats what is causing it, and i aint used for a week, werent sure if aa man would be able to diagnose that, i will ring them in morning and see what they say. cheers for the help. also could someone tell me if that light will stay on permanently now even if the problem goes away ie it dries out? or does it have to be manually switched off??

If it is just coil packs the light will go off eventually, but I am worried that it is staying on... I strongly recommend you speak to someone at a Porsche Specialist before you drive the car... I'm sure it says in the handbook don't drive it if the light stays on? It is a dual function light, and IIRC flashing means your emissions are being compromised through unburnt fuel entering the catalytic convertors, whereas staying on is actually an engine problem. Might have got that the wrong way round though - anyone else know? Even if it is just the misfire, get it fixed ASAP: The longer you leave it, the greater the chance of wrecking your cats - and that's expensive!!!

I'd suspect also(as well as one of the coils) one or more oxygen sensor failures(an OBD download should tell but also see extract from one of my 996 stored library files below: BTW - avoid opening the taps to try and clear the issue as you will almost certainly overfuel the engine then knacker the CAT(or worse start a fire) by doing so. Get it uplifted to the OPC/Indy "The check engine light (CEL) is a warning indicator: it means your car's computer has determined that a component or system in your emission controls is not working properly. If the Check Engine Light illuminates, stays on, and there are performance problems. This means that a vital component of your emission-control and engine-management system has a serious problem. It usually involves a component or system needed for the vehicle to run at all. In most cases, drive the vehicle as little as possible. In many cases, the vehicle is not safe to drive at all"”it could stop or stall out at any moment. It is best to pull over to a safe place and have the vehicle towed to a Porsche garage for inspection and repair. or The Check Engine Light light comes on and blinks in a steady pattern while driving. Don't confuse this steady pulsing of the Check Engine Light light (usually one or more flashes per second) with a flicker (see above). The Check Engine Light may stay on steadily, or it may flash when the vehicle is accelerated. This is very serious. There is a severe failure of the emission-control system that is causing the engine to misfire to the point that the catalytic converter is damaged each time the Check Engine Light flashes. It may mean that the catalytic converter is overheating to the point that it will glow red or, in extreme cases, start a fire on the underside of the vehicle. Immediately pull over to a safe place and have your vehicle towed to an garage for repair. Vehicles can be/are often severely damaged and even destroyed by fire if this condition is ignored for too long."

dont worry guys i wont drive it, i will ring the malton garage tomorrow morning, get it booked in, i will also get the aa to come and have a look, we live on a hill and thwe last 2 days have been misty and raining all day, i can only think the weather has got to the coils cheers neil.

right been a nice mild day today, had to go see how it was,started it and it runs perfect again but the light is still on, can you tell me if this can be reset by me?? it is defo running fine no misses or coughs?

Do you want your engine to pop it's clogs? You should NEVER run any 911 with the CEL on under ANY circumstances.....unless it's an emergency situation It's £8k for a new engine vs a few hundred pounds to get it to an OPC?/Indy...you chose :hand: :hand: :hand:

Ermm... Says in the handbook that it might affect your emissions and ultimately damage the Cats... Hardly new engine territory! My money is on split coils... The light will go out if you get a few dry runs in, but it will not go away: Once the coil pack is split it will short every time it rains and eventually will damage your cats. Strongly recommend you get it fixed ASAP.

I really have to agree with Wizard & Wattie here. Regardless of whether the car is now running fine or not, something triggered that CEL and any CEL is not to be taken lightly...

Make sure you have your radio code?. Disconnect your battery for 20 min(this will clear the ECU/CEL warning) Reconnect your battery and fire it up. The rest is up to you/ and entirely at your own risk.... .....you may get 10/20 miles (providing the CEL stays off :hand: ) to nurse it to the OPC/Indy. If you are doing this please keep the revs under 3k rpm and avoid any sudden depression on the gas pedal......don't idle/warm up the car either just get it to the garage ASAP. Your main concern here is overfueling - unspent petrol gathers in the CATS and can catch fire.......believe me you will need a new engine if this happens....and maybe a new car! If it was mine and the CEL came/comes on I'd cough up the dough to get the car uplifted to an OPC/Indy BTW - get a friend to follow you to the garage as 911's with CEL's illuminated can/do break down.