DrRobin

It has turned out to be coils, all 6 had at least one hairline crack. I obtained new Beru coils and sin new spark plugs, fitted yesterday and all is now good. i had replacement coils at 55k miles and now again at 93k miles, not sure what causes them to fail, but they don’t seem to last that long.

OK, I can answer my own question, the vac take off goes to in the throttle body T tube, top left in the photo in the previous post. I will need to check mine is in the right place.

I wonder if you can help me determine the location of the vacuum lines in the rubber connectors on the intake tubes? In the attached image above, the front tube (flapper?) has a butterfly valve controlled by vacuum and then in the rubber connecting tube (right hand side in this photo) there is a vacuum take off. The rubber connecting tube on the left hand side also has a vacuum take off (see photo below), should this be on the tube connected to the throttle body (rear) or on the tube at the front? I think it should be on the tube connected to the throttle body, but I can't find an image anywhere to confirm. I think that the vacuum take off at the bottom of the picture (above) might be on the flapper tube and not the throttle body tube. I am not sure how much difference this would make? Hopefully someone can set me straight.

With the engine at idle, I tried removing the oil filler cap. There was a slight vacuum holding it in, but it removed okay. As soon as it was removed the engine note changed and it sounded more un-even. I think this means that the crankcase vacuum and AOS are both okay? Just another question, the air intakes, straight after the throttle body there is a diverter (T shaped tube) that allows air to both plenums, but then at the front there is another connecting pipe with a vacuum operated butterfly valve in it. I assume that this is some sort of balancer pipe, but when does the valve operate, at small throttle openings when the inlet vacuum is high? Can anyone let me know what function this provides please? I don't think there is any problem with this, just curious.

I took the throttle body off, there was some black deposits around the opening (see photo), but overall it was fairly clean. There was a small amount of [clean] oil in the black plastic tube after the throttle body and small amounts in the plenum and second plastic tube with the valve in it (see photo). The oil wasn't excessive and I changed the AOS last year, then there was a lot of oil residue in there. A short test run and it is may be slightly better, but still a little rough at low revs/throttle openings. I don't get any fault codes and don't have a misfire (since charging the battery) so I now suspect coils or plugs. Coils were changed in 2008 at 52k miles, plugs I can't find when they were last done, I am sure they have been changed, but can't find a record. I can't find the exact service interval for plugs, I see it quoted as 24k or 40k miles, so think I will have a look next chance I get.

I haven’t checked either yet, but will have a look next chance I get.

Hi, I had my 2001 2.7L Boxster serviced in June and all was fine, it has done 93,000 miles. A week or two later noticed an increased noise from the exhaust and on closer inspection there was a small hole in the CAT on Bank 1 (drivers side in the UK). I got two CATs and had my local garage fit them (now July), no problems there and then filled up on the way home at a garage I don't normally go to as the tank was low. The next few days I had random misfires, but only after deceleration and at low revs (less than 2,000 rpm) when feeding the power back in. The misfire was random (sometimes cylinder 1, then 6, then 2, then 4). I thought may be dirty fuel. My OBD-II code reader showed ageing on all four O2 sensors, I guess they were just old and swapping them over into the new CATs finished them off. After a long wait to get new sensors (now August), I decided to fit them myself, the old ones were difficult to get out of the new CATs, so I took both CATs off, fitted the new O2 sensors and all faults cleared with none coming back. I took it for a test drive, no misfire and back to normal. Roll on another week and the misfire was back, but not all of the time. I tried a fuel cleaner and a couple of tanks of good fuel from my regular garage, but still got the odd misfire. I then noticed that the battery was quite low and had been for some time, so recharged up to full on a recovery charge, the result no more misfire, although the engine is not running as clean as it was. There is no problem at idle or when pulling, it's at small throttle openings or slow speed, it's not a misfire, but it isn't running very cleanly, so since O2 sensors was the last thing I have gone back to those. I initially thought that the output looked normal, the two sensors pre-CAT move from rich to lean in nice smooth graphs and the post CAT sensors are fairly smooth, so I tried a re-learn and it was then that I noticed that Bank 1 Sensor 2 (Post CAT) is sitting at 0.2V soon after starting whilst Bank 2 Sensor 2 is 0.50V. Once the engine warms up Bank 1 Sensor 2 does come up to around 0.5V when the car is driven, but soon drops to a fairly low voltage when idling, this shows the sensor is working but may be the heater isn't, is that what you would think? You can see the big difference in the attached screenshot from Torque Pro. I know Sensor 1 is used to set the mixture and thought that Sensor 2 is used to test the CAT, but is Sensor 2 also used to set the long term fuel trim and could a faulty heater in one sensor post CAT cause rough running? Robin