911SC erratic idle from cold

[Anconablue72]

Hi to all,

I wondering if any of you out there have had similar niggling problems and what the eventual resolution & cost was,

Last weekend i fitted a Dansk 84mm single pile silencer and had to adjust the idle as i expected just after,

my (Swiss) handbook says 750-800 rpm but Wayne Dempsys engine rebuild book says 900 rpm,several people have told me several different things so, is there anyone out there with an SC care to divulge their idle rpm? and does it vary according to the ambient temperature?

 

This weekend i carried out the first service (12k) its had in my ownership, and cured several oil leaks and done a general tidy up, its an 83' sc Swiss import, 150k, not burning oil and generally very quick and reliable, and was running (until yesterday) an airpump,

Yep i've been persuaded to rip it off,

Apart from the visual improvment you can actually see where the plugs & leads go,

 

I know most of you out there have removed these pumps, the vacuam line running from the pump to the airbox, just plug it? anyone noticed and difference in how the engine runs/idles? my idle has always been a bit erratic from day one, when started from cold it has always hunted badly reving itself for the first 25-30 seconds on a cold start up, eventually settling down, hot and cold starts are always instant on the key but with cold starts there is the very annoying fluctuating idle.

Now with the air pump removed it apears a little worse, im assuming that's because the engine revs more freely now there is a little less load/drag from the air pump to dampen it??

It may make more horsepower available but its done nothing for my erratic idle which is now worse...even when warm it fluctuates but not a badly as when cold,i can manually adjust it but when engine hot its set to 850/00rpm this wil change next time driven and only at hald operating temp which can be very annoying to suddenly get a very low idle if in traffic,

To corrct this idle problem ive done/checked the following:-

 

Full engine service, plugs/filters(fuel/oil),oil,dizzy cap/rotor arm,valve adjust,belt,

 

Fitted a replacment reconditioned(German) idle regulator (unit that sits between the first two intake manifod pipes on left of engine) interestingly both new and old tested 35ohms across the two terminals?? so maybe my old one was ok?

 

Ive cleaned all the terminals in the electrical sockets /plugs in engine bay and on engine,(that i could find anyway)

 

I have checked for the obvious vacuam leaks and cracks in the manifold rubbers,airbox free of splits, and all the plugs burning same/equally.

 

I use it every day and to be honest im not really looking forward to using it next week as it is now, when used daily you really notice the niggling little things like a low or high idle, sometimes a slow return to idle etc, so im keen to get this problem sorted,

Can anyone out there suggest anything ive missed or what to try next (other than take to a dealers and cellotape a blank cheque to the dashboard)

Could an incorrect mixture setting affect only the idle when cold? it rn very very wellthe rest of the time , pulls very hard in all gears even fully loaded,

Any idead would be most appreciated,

Thanks n advance,

Chris

[nick]

Hi Chris, I too have a 1983 911sc which did exactly what yours is doing, the vacuum hose from the pump, yes just cut it short and superglue a self tapper into it.

 

My idle was very irratic like yours until warm when it would even out at around 850-900rpm I have since solved this by replacing the warm up regulator but in turn had to adjust idle and mixture to get it running ok, although it never starts first time now always second which I don't mind compared with the annoying revving before.

 

In case you are not sure the WUR is to the left as you look at the engine sitting in between the inlet manifolds, it has a vacuum hose fitting either end and a couple of the rigid fuel lines feeding in to it and an electronic sensor.

 

Hope this helps

[johndglynn]

You guys need to get your mixtures/CO levels checked etc IMO. Your car should start first click of the key Nick. The mixture screw on an SC is counterintuitive; on most cars you will screw it in to lean it out but on an SC you unscrew it to go lean, so if you have played with your mixtures you could all be running rich as hell. My buddy Bob Watson taught me that, and says it is the most common problem with sick-sounding SCs

 

Get it on a dyno/CO meter or something and check the fuelling would be my advice.

[Anconablue72]

Hi Chris, I too have a 1983 911sc which did exactly what yours is doing, the vacuum hose from the pump, yes just cut it short and superglue a self tapper into it.

 

My idle was very irratic like yours until warm when it would even out at around 850-900rpm I have since solved this by replacing the warm up regulator but in turn had to adjust idle and mixture to get it running ok, although it never starts first time now always second which I don't mind compared with the annoying revving before.

 

In case you are not sure the WUR is to the left as you look at the engine sitting in between the inlet manifolds, it has a vacuum hose fitting either end and a couple of the rigid fuel lines feeding in to it and an electronic sensor.

 

Hope this helps

thanks for he reply, i have changed the WUR for a german reconditioned one but it hasnt made any difference, i have access to an auxillory air valve so will try this next,

i was hoping to find the faulty unit and replace it then (as John uggested)end it off to someone who knows exactly what they are doing for a mixture set up and timing/emissions set up once and for all, my pals old sc idled and run really well ,mines quicker but more annoying! i treated it last week to a good going over and a s/steel silencer and today to a sports s/steel pre silencer(straight thru pipe) and it sounds awsome, but still got a crappy idle........worse than women...

[johndglynn]

Rev'd, I would stop changing things and get the mixture set now if I was you, there will be an acre of difference between what you have with and without the air pump. Air pump removal is how myself and Bob Watson got on to the subject of silly-rich mixtures on SCs - it creates all kinds of problems but ultimately is the only way to go of course.

 

What did you use to plug the injector holes underneath - did you go for the Porscheshop kit or leave the injectors in situ and dab a blob of weld on the lines? Any chance one is leaking? The one up behind the o/s heat exchanger?

[Anconablue72]

Rev'd, I would stop changing things and get the mixture set now if I was you, there will be an acre of difference between what you have with and without the air pump. Air pump removal is how myself and Bob Watson got on to the subject of silly-rich mixtures on SCs - it creates all kinds of problems but ultimately is the only way to go of course.

 

What did you use to plug the injector holes underneath - did you go for the Porscheshop kit or leave the injectors in situ and dab a blob of weld on the lines? Any chance one is leaking? The one up behind the o/s heat exchanger?

your right it will need checking but i had to drive it today and it was terrible, and as luck would have it there was the biggest traffic jam on the way home ive encountered this year!! its now back in the garage until i get time....

i had a brief look lunchtime and run it with the airbox lid and filter off to observe exactly whats happenin , the arm which actuates the airflow sensor in the air box ? (the round flat plate that lifts with increase airfolw) it rests at idle and as engine falters it surges and the plate is drawn up allowing engine to breath,but it continually fluctuates hence the revving up and down, it looks like here is no flow of air available to bypass the sensor plate and throttle butterfly on idle hence the engine sucks the plate up (injecting fuel at same time) and so the cycle continues, it looks like the air valve could be at fault, but ive not yet had chance to check for voltage/operation etc, look to see where pipes actuall go to but logis says there must be an air path on idle to bypass the sensor and throttle ousing somewhere, maybetomorrow i'll get time to read a manual??

Any one now what the voltage should be at the terminals? 12v? is the airvalve opened by voltage when sensor plate drops down or is it the otherway round no voltage closed it?

Is it a basic on off unit or does it have gradual increments of ait passage thru it?

maybe its time for some PMO's...

[MBEngineering]

HI your car should have ; ignition timing 25deg bef/tdc, at 4000 rpm. vac disconected.

Fuel system presure 4.5-5.2 bar, control pressure 0.9-1.3 without vac, 1.6-2.0 with,

control pressure at idle 3.6+/- 0.2.

CO 1.0-2.0% (with aux' air injection disconnected).

You need to check the settings out ,befor you start to swap things. If you can find the info ,porsche had a book "Troubelshooting Guide K-Jetrioic " part No 4533.20, if you can not locate one PM me and I will see if I can sort this one out ,as it is now a little worn.

 

regards mike

[Anconablue72]

Well i got the SC back from my local specialist La' Rose,

Its the first time i've actually used them but they came recomended by a work colleague who has had his 73'Targa in there a couple of times and i must say my very first encounter with a 'garage' went fairly smoothly, my bill was £299.17, to be honest i was expecting a real whopper of a bill, however after a thorough engine/elec compoment check over they established all was`ok and the fuel delivery side of stuff was spot on but the mixture was seriously over rich, following proper adjustment/setting up it actually idles perfectly, which as you can imagine has made driving it even more enjoyble, it means also that: 1, i did'nt miss anything glaringly obvious, and 2, it meant i did'nt have to spend bundles of hard earned cash.

The down(ish) side was that when the fuel pressures were being checked the corroded fuel line fitting sprung a leak, rather there than in France i guess, but no replacement pipes were available in the UK main dealers so the new one had to be sent from Germany which delayed its return over he weekend but it was'nt a problem,

So now back and its running good, feels much stronger and it ticks perfectly, i've yet to see if its any better on fuel but i'm well chuffed, and would definately use them again,

thanks to those who replied to the earlier posting regarding possible causes

Cheers