996TT manual high revs when idle and occasional misfire

I had my high mileage 996TT for over a year (128k miles) and other than a radiator leak it and fan replacement it has been fine. The car has a spotless maintenance record with last 13 years looked after by same indy. I recently notice that after the car warms up sometime randomly the idle revs are high (1.3krpm) and when idle sometime revs drop and go back up again. Also recently when doing a couple more aggressive short drives into higher revs, when then driving at lower revs, the engine seems misfire but next time i use it it seems fine as long as i dont drive it agressivly. A couple weeks back, the ABS / PSC light also came up but when i restarted the engine it has gone and has not reappeared since. The battery is 1y old and i never had any electric issues with the car. I am planning to go back this week to my indy but any ideas what it might be (and cost)? Thanks

Check for a leak in your intake - I had a high idle and a bit rough low-speed running and it was because the intake pipe was split just after it comes out of the airbox - didn't have a misfire mind you. I needed a new airbox, which I got for 250 used off ebay. The plastic gave up over the years, and it takes a bit of force with airbox coming in/out to change the air filter - I suspect that's what happened to mine. The MAF is plugged into the hard part of the line which is part of the airbox and the split was after it, hence the MAF is measuring the air coming in, but then the actual air being drawn into the intake is of a different volume and thus the car fuelling doesn't match the actual intake air volume and the car doesn't run properly - I could only see this as I was going to clean the MAF and noticed the split - i'm not sure it was visible just from looking at it all installed. And given you are in at that part of the system, a bad MAF can cause the ABS light to come on as well, although in my case (where a restart would clear the error), it was a broken loom to the ABS on the front nearside, which is a common 996 fault and it's cheap enough to buy a new loom kit for it (about 70 quid, simple to fit with wheel off IIRC) - but reading the live data can show whether the MAF is fine or not. MAF gets blamed for a lot of things that rarely ever seem to be the MAF! If a MAF is overfuelling, then that might indeed present itself as some rough running after a bought of high revs, but not a misfire (if thats indeed what it is). Anyway, this is all conjecture - I'm sure your indy will find it once they read codes / check the data coming out of the sensors. Never throw parts at a problem when it's not clear what the problem is!

Mine has very recently developed a higher than normal idle, I haven't investigated it yet, I have however done some Internet searches and two things came up, the first as mentioned above was intake leaks, the second was the maf!

Nmartins, have you sorted your high idle?

Hi. I called my indy, and they told me to turn the car on and leave it without starting the engine for about a minute until I hear a ticking noise from the engine. When you turn on the key it makes a humming noise at first, then goes quiet, and after about a minute starts ticking. Apparently, this resets something in the electronics and recalibrates the idle revs.For now, it seems to have worked but to be honest, I've only done a couple of short drives since I did the "reset", so I haven't fully tested it yet. However, so far so good. During the short drives, and when I got back home, the idle revs seemed normal, staying stable below 1,000 rpm. For now and for a change an easy cost free fix! Fingers crossed that it stays like that but porsche anxiety starting to kick in again

This is what my web search told me what it seems to make sense The 996 Turbo uses an electronic throttle ("e-gas") rather than a mechanical throttle cable. When you switch the ignition on, the DME (engine ECU) performs various checks and calibrations. One of these is the throttle body learning its fully closed and fully open reference positions. During this process you may hear humming, whirring, clicking or ticking noises from the engine bay. If the throttle adaptation had become slightly confused due to: a weak/disconnected battery, flat battery, ECU power loss, throttle body cleaning, electrical glitches, then allowing the ignition-on adaptation cycle to complete can sometimes improve idle stability.

It won’t be that