Since I've had my S it has suffered from a poor cold idle (almost stalling when maneuvering, etc) but recently it started playing up when warm, and stalling in traffic. I came home to sunshine on Wednesday afternoon so decided to remove the inlet to have a good look around. Apologies for the phone pics!
I had already identified a cracked breather pipe between the AOS and inlet, so had a new one of these ready to fit. Once removed I found that the TB was quite dirty on the manifold side, and the inlet manifold runners had quite a thick coating of oily residue in the runners. The injectors were very stubborn, but once removed it gave me a chance to give the inlet a good clean, as well as the TB.
Inlet & TB cleanup by
Hallsy01, on Flickr
Inlet & TB cleanup by
Hallsy01, on Flickr
I had also tested the TPS, the idle switch was working fine, but it seemed that the WOT switch was not. However, after removing the cover I found that both switches were in fact working OK, so either it had miraculously cured itself, or I had slipped with my meter probes!! I did find that the throttle stop was not actually contacting the throttle arm and the plate would bind a little when closed. I adjusted the throttle stop until it just contacted the closed plate, and then wound it on another 1/4 turn. Re-adjusted the idle switch and the TB was good to go.
I then pressure tested the intake pipework (had to get inventive with the bungs!) and found it was holding pressure fine at 5psi, so in terms of vacuum, it should be OK:
20140228_093945 by
Hallsy01, on Flickr
The small more pipework that runs under the IM tested OK as well, but I replaced the elbows & T-pieces anyway while I had the opportunity.
The ISV was fairly dirty inside, so I cleaned that up and tested operation - all OK. Also replaced the ISV mounts.
The AFM had had the wiper arm moved before, but I still wanted to give it a proper bench test. The voltage output was nice and smooth, and the air temp sensor resistance was within spec:
20140227_122014 by
Hallsy01, on Flickr
While I had access I also tested the knock sensors and DME temp sensor, again, resistance was within spec for both.
The AOS seals are a common leak point, and sure enough, mine were showing signs of leakage with oil around the ports. Once removed it I had some cleaning up to do!
944 AOS Clean by
Hallsy01, on Flickr
944 AOS Clean by
Hallsy01, on Flickr
Now nice and clean (apart from some staining), lid seal was greased, port seals were replaced. I also fitted a new oil filler cap:
944 AOS Clean by
Hallsy01, on Flickr
Today I put it all back on the car with a new inlet manifold gasket. First start up and the idle still sounded a little rough, maybe there is still a problem, or maybe it was down to the initial lack of fuel and DME reset. Once on the road there was a big improvement, part throttle and overrun was much improved. Previously the car felt like it had too much engine braking on overrun (or a bit like the handbrake was sticking), now it feels much better. Feels a little more free revving as well, and pulls well up top. Once warm the idle was spot on, it would quickly return to ~1000rpm before gently dropping to ~800rpm.
I'm not sure whether the DME would have gone through any adaption process as I only had time for a quick 15 minute drive, but will give the car a good run tomorrow and have a better idea of whether the cold idle is improved.
Hopefully it's not placebo effect, lol!!