Prior to today, my valver was running just fine. I have had a stalling issue that I seemed to cure by adjusting the idle screw on the throttle body and bringing the idle from around 900/950 to probably around 1050 - been driving and starting pretty much trouble free for a couple of weeks now. However I thought it felt a little sluggish and so decided to get the idle and CO set properly using my gastester.
I reduced the idle speed from approx 1100rpm to around 980/1000 rpm (according to the MFA secret function). I stuck the gastester on the tailpipe and found my CO was at almost dead on 1% and so increased it to 2% (give or take 0.01%). At this stage the idle was pretty solid (some very slight movement on the needle, but blink and you'd miss it), engine sounded smooth and healthy etc.
When the car is hot, and at normal running temp, however after reconnecting the coil spade connector and the breather pipe from the ISV, back to the air intake pipe, I get a whole variety of weird things.
At idle, my revs can seem to rapidly twitch between approx 850 and 1100 rpm - as if someone was very delicately feathering the accelerator. If you tap the throttle pedal, the revs will rise and then drop just past idle before climbing back to normal. If you rev it beyond say 3000rpm then it fall to around 500rpm before recovering - do it really hard and the car will come very close to stalling (once or twice it did stall when revved hard to 5000rpm ish). Lastly, I noticed at very low revs, with the clutch on/around the bite point, it will really struggle not to stall, and when reverse parking I stalled it 3 or 4 times when usually I would be able to edge the car backwards. It really feels like it's struggling with reverse gear. I've also noticed that the revs drop very slightly at idle when I switch the headlights on or when the fan kicks in. The wobbly idle (twitch between approx 850 and 1100 rpm) is loads worse with the fan running too.
However! If I disconnect the breather pipe from the ISV and plug up the airbox side, it seems fine. Rev's at idle aren't totally solid, there is still that slight movement on the needle, but reverse and hard revs don't seem to make it want to stall.
ISV seems the target, no? It is buzzing when ignition is turned to position 1, and I have cleaned it out thoroughly with carb cleaner. But the problem persists.
Any clues? If the breather pipe is just routing back to let the engine breath etc, why should it have such an effect when connected to the ISV?
I'm now wondering whether the fact I used the idle screw to keep idle slightly higher than 1000rpm might have disguised the fact the old problem hadn't gone away, and the idle screw was compensating in some way?
Just tried the car again, this time from stone cold.
With the breather pipe disconnected and the airbox plugged, it wouldn't even maintain idle from a start. It would be hesitant to start, get to idle and gradually drop off to around 500rpm before stalling. Did it a couple of times.
I reconnected the breather pipe and the car started and idled OK, but a moderately aggressive rev of the engine and it died. Drove off fine if I didn't rev its tits off, and as an experiment half way up the road I dipped the clutch when the car was revving around 3.5k rpm and the engine stalled again. Continued driving, and I suspect as the engine warmed up by this point the stall issue disappeared. Drove around loads, some of it quite 'enthusiastic', no issues to speak of. Dipping the clutch even at say 5k rpm and the revs drop to just above 1000rpm before settling. Got it home, sat with the car idling, and the slight change in idle speed is noticable - can't be more than a 100 rpm difference but you can see the needle move ever so slightly and the engine noise increases and decreases in pitch. One thing, revving again causes the revs to slightly dip below idle as they fall before recovering. As I say, it only seems to do this at idle not whilst driving (see above for the 5k example).
Is the ISV shafted? It has the part number 037 906 457c.
