Re: Think Ive Sorted Idle Problems
Yes, I was trying to avoid heavy theory and just give a pointer but if that air intake gets blocked the actuator will have an incorrect comparison level between vacuum and atmospheric pressures.
I haven't had time to clean mine because I want to carry out tests and observe what it affects at the same time but obviously my initial suspicions are it delaying or at worst case stopping the manifold length change.
Also I can't find the main engine air intake which normally comes via a pipe after the air filter on most cars, according to the manual the engine also draws some air down into the rocker cover through that valve on the actuator.
If the engine needs that air for purging smog so instead trys to draw it through the breathers it would result in oil not returning freely to the sump and also mess up the expected pressures at the intake mainfold and affect running especially once warm at low RPM. (Hence Andy's magic cure?)
The canister purge valve is listed on an Alfa Romeo website for dealers to locate common idle faults. Apparantly screen wash or rain water run-off from the grill under the windscreen can get through a gap at the top of the inner wing and contaminate or corrode the valve, they recommend sorting the valve out then blocking the gap off by cutting a rubber block to mastic in place.
I asked in a previous thread on here but no-one could tell me where to find the canister and I hadn't found it by following the pipes. I didn't know it was inside the wing until I found the manual I pinched the picture from. Before that I had also assumed the 2 fuel pipes were flow and return rather than both flow, with the second one coming into use only after petrol fume pressure exceeds a certain limit, that's why I thought to check the valve under the throttle body as if it doesn't tell the ECU it's open the engine will run rich when it is. Presumably this problem would be worse on hot days when petrol evaporates more or if you fill up and run on a whole tank for a while rather than puttting in smaller amounts of petrol more regularly thus venting the system by taking out the filler cap.
So if you're idle problem goes away when it's cold and wet or by running with the filler cap loose there's the probable answer.
The short answer is yes, I'll try to explain it in plainer English this time lol.
As an engine wears, especially the bores & rings, crankcase pressure builds forcing more power robbing smog into the intake system and wet oil residues that coat lambda probes. My trade meant I have averaged 80,000 miles a year upwards and I have had Subarus and Volvos do 200,000+ miles without wet oil residues but the Alfa twin sparks seem to start getting them around 100,000 miles.
So taking it away results in cleaner running and more power as Andy has found, plus you should stop killing lambdas.
There are 2 big "BUTs" if you do this though:
1) On a high mileage car around 50% of it's carbon emmissions are from this smog which is why just venting it to atmosphere means an MOT fail and is not even allowed through scrutineering on track days.
2) Regardless of whether you don't want the smog in the combustion process the whole system is designed so that by connecting it to the intake vacuum it actively sucks out the smog from the crankcase thus keeping crankcase pressure down. (on drag strip cars they often use an electric vacuum pump to do this)
So if you unbalance the whole system sooner or later the excess crank case pressure will result in blown gaskets or seals. If you google you can find umpteen people that have tried what Andy has done that this has happened to which is why I was concerned about his engine and trying to warn him.
This is why I was recommending using an external oil separator like they fit as standard to very high RPM engines, turbo charged ones or track cars. It is a good compromise until you can't get away without a rebore any longer as you avoid the worst parts of the smog going into the injection system, still get your engine actively vented and can still get an MOT without putting all the breathers back to standard before going.
There is a very basic oil separator inside that black plastic box where the pipes connect to the rocker cover, you can try to improve it's efficiency (packing it with more steel wool is a common DIY trick) to delay buying an external separator or having a rebore. The idea is to stop the heavy wet crankcase fumes but not impede the exit of the pressure causing gasses.
I think people who looked at the previous post were put off by the theory link showing the need to drill and tap a return oil flow line from the external separator into the sump. You don't need to do this, if you prefer just run the output of the separator to a catch tank and empty it when the sight level shows it's full.
Glad you've sorted the starting problem, that makes sense, if the battery wasn't rated for enough cranking amps (People often just check the main amp hours rating and forget the cranking one) then the ECU and sensors wouldn't be getting a full 12 volts + to work with while it was turning over on the starter.
Hope the above was some help and not just gobbledegook, Im more used to showing what's going on than explaining it and often been told I'd never have made a good teacher.