1981 SC CIS - low idle - wrong WUR?

[RDM]

Originally Posted by wreckah

gratuitous shot of my former 69 T...it was a beauty.

Beautiful. I had a 69 E in Bahama Yellow that I still miss.

[wreckah]

WUR resistance...13 ohms
around 10°C now

[boyt911sc]

Originally Posted by wreckah

WUR resistance...13 ohms
around 10°C now

Jan,

Ask your friend to check the WUR resistance of the WUR-072 in his car when the engine is cold. And compare the values (Ohms) between these WUR-072's. Post the data. Your WUR is out of spec. and would always cause this erratic cold idle. This problem will not go away until you install a good working WUR. Lastly, stay away from tinkering your mixture setting because it has nothing to do with your erratic cold idle problem. Keep us posted.

Tony

[wreckah]

my friend doesn't know how to measure that, will have to go by his place and do it myself.

in the meantime, been digging a bit further while waiting for a duty cycle meter to arrive:

- checked the 15°C sensor: OK
- then i wanted to check the air flow sensor position (which is OK) and by taking off a couple of things (cruise control cable etc), i noticed that the throttle lever did not touch the 15 degree position switch! so the switch was open all the time...this is a cold enrichment thing, so i guess that has not helped my cold running issues. I managed to reposition it, and bend back the throttle lever to it's original shape, and now it's functioning properly. The switch itself measured OK.
- next up the list is the butterfly: the base positioning looks too crooked as far as i can tell (need smaller mirror), probably 2 or 3mm height difference between both sides of the butterfly...i think this should be a little less. Can anyone confirm that the closed butterfly should be following the horizontal edge in the throttle body more closely? I know it shouldn't hit the housing.

[wreckah]

ok guys, started the car this morning at around freezing temp, starts first time, but idles at 500rpm. It seems to start and run a bit easier now i have corrected the 15 degree switch. It holds the 500rpm without any problem, not fluctuating, not stumbling.

In order to further troubleshoot: can anyone explain me why i can simply raise the cold rpm by turning the idle air bypass screw and i cannot raise the rpm by using the (working) AAR?
These things both give bypass air, right. Is it because the AAR takes the air from the boot and maybe changes the air flow sensor position slightly?

when the car idles cold i've checked the following:
- unplugged the fat aluminium AAR vacuum line, plugged both sides. no difference in cold running.
- When i take off the plug on either side, the engine stalls immediately. so the lines are definately not blocked and pulling air.
- when the engine is idleing, when i push or pull ever so slightly on the air flow sensor, the engine dies.

thanks for thinking along,
cheers, Jan

PS it seems anal to be bothered about such a small problem...'i could simply hold the rpm's up with the throttle for 30 secs and done'...but by searching for problems and causes you really get an understanding of the system, which IMO is definately worth the effort.

[Vereeken]

The aar uses air that is already measured
It does not increase the lift of the sensor plate
The idle valve does increase the lift of the sensor plate as it increases the drawn air
The aar only Lets through air following the amount of opening but does not suck in more air then already present in the systeem

[wreckah]

OK, my buddies US 80 SC 072 WUR has 11 ohms at approx. 7°C...

doesn't really matter right now, took the valve covers off for setting the clearance, and found 3 broken headstuds, guess we found the reason for the oil leaks.
the engine is already been dropped, disassembled and brought to specialised firm to overhaul...full cylinderhead revision, cleaning up of pistons and cylinders (they luckily still look good), and they're going to take out the headstuds, and open the case and have a look at the crank for good measure.

No vacation this year

[Riseabv]

Originally Posted by wreckah

Hi guys,

i've got this 1981 911 Targa with some cold running issues, and i would love some input from you lot, i've done lots of research but i'm reaching a ceiling on my knowledge...

the car is mostly stock, and in pretty good condition, inside and out, original california car, so US spec. Weinrot.
I know i need to post a pic, so here goes :


I just did some pressure testing and here are my results (all with non running engine, bridged the FP relay, so non vacuum):
cold control: 1.6bar (around 5 to 10°C here in Belgium at the moment)
warm control: 3.4bar (reaches after 3-4 minutes when i plug it in)
system pressure: 4.5bar
(fuel pump sound good, also no fuel leaks whatsoever)
i haven't got any residual figures because the fuel pressure tester is leaking a tiny bit in one of the connections. (i don't think it has influenced the numbers too much)

Worth mentioning: the car has no O2 sensor attached, and is running a 072 WUR,
the AAR is working good, and i did not find any vacuum leaks so far...

Issues: cold start is not great: it will start relatively easily, but never reaches high rpm...it idles (barely) at 500rpm and is very temperamental the first couple of minutes. It will stall too if i give it some throttle and then let go of the throttle. After a while, stumbles go away, and the car feels quite good once warmed up. Warm idle is rock steady at 950rpm.

It seems that warm and cold control pressures are a bit on the high side. Although it smells very rich, which is strange? It should be too lean when cold with these numbers, right?
I made the WUR adjustable for CCP, so that will be a reasonably easy fix, push it in a little bit and measure again. I opened it as well, and it looks brand new in there. Is it also adjustable for WCP? Is this WUR correct for this car?

I wonder why it keeps this low rpm when cold...any other things i should check?

cheers for the input,
Jan

Sorry it's unrelated but where did you purchase the RUF CTR front bumper? How is fitment? It looks great, I intend on putting one on my SC.

[wreckah]

hi there,

i don't know which brand the bumpers are, nor where the PO bought them...they were on the car when i bought it. Fitment is OK, but it is FG so you can't compare it to OEM stuff.

in the meantime, the engine has been professionally overhauled from top to bottom, 12K € but it doesn't really matter...brand new engine now, also brand new clutch kit, etc etc...the full list is 2 pages long. Sortof lucky too, as we discovered that the clutch was almost worn to the rivets, and also we found a broken valve spring in one of the cylinderheads. So it was time to look at it.

i still have the cold start issues, but for now, i'm gonna leave it be and just drive the thing. It always starts but runs like **** for 10 seconds. After that it is fine. It drives wonderful by the way, much smoother sound (now that the cylinders are effectively airtight ) , much less vibrations, no leaks, and after about 600 miles she appears to use 0,0l oil. I've run it in perfectly, next week oil and filter change (porsche classic oil).

[Irhmsd]

Though completely over my head, this is an amazing thread.....so many super smart guys on here.

[T77911S]

check the AAR. it should be open when cold and it should close when heated.
sounds like it might be stuck. if it is remove it and try some carb cleaner in it..

both the AAR and the idle adjustment use air that has already been metered by the AFM., if you increase the idle with either one it is just like putting your foot on the gas.
same goes for the AAV. that is open only when cranking. it closes after it is started.

may not be related but since you have a new motor you have the injectors cleaned and checked.

I saw something about vac advance. that does not do anything at idle.

[wreckah]

the AAR works correctly, i checked that a while ago.
The car drives perfect after one minute, and when fully warm, etc...

i adjusted the WUR both leaner and richer (cold control), but both ways have no impact on cold low idle.

how can i easily check if the csv mounting is unblocked? I've read a couple of stories about the csv mounting flange with blocked air outlet...which means that AAR and decel valve etc...would not have any effect.

[wreckah]

i could disconnect the vacuum line from the back of the boot to the AAR/decelvalve and see if the engine pulls vacuum from that line, correct? (close the hole in the boot while trying)

[wreckah]

OK, got myself a duty cycle meter, and with cold engine i'm getting 35 on the readout...which means 65% duty cycle i guess.
Pushing the throttle slightly temporarily reduces the reading to 25, then back to 35, so that is very correct for now.
Gonna go out and warm the car up thoroughly in an hour or so, then do some more measurements.

I have a O2 sensor on order as well, gonna get it tomorrow, wire it in, and see where we go from there.

[wreckah]

yapp, i like the color very much

just went out for a drive, engine nice and hot, 50% duty cycle, so that's all working OK,
let's see what the mounting of the 02 sensor will bring.

i made the WUR adjustable, and fooling around with that changes cold starts from very poor and stuttery to 'sort of OK'...but always with low idle. after less than a minute the car idles fine, and accepts throttle very nicely. Once warm, it is brilliant.

I've finished running it in too, checked all the valves (all perfect) and changed to Porsche Classic 10W-60 oil. It hasn't used or lost a drop of oil since rebuilding.
I have to say, touching 6500rpm is an almost lifechanging experience

[wreckah]

OK, i wired in a bosch 501 one-wire 02 sensor, warmed up the car and checked mixture and duty cycle.

i was not far off with my 'setting on hearing'...maybe 1/8th of a turn.

great to see the duty cycle change when you turn the mixture screw, i saw it nicely dropping and rising by turning left or right on the screw. I have set it now at ca. 50%.

I think i picked up some low down horsepower too, it feels more crisp from 2000 to 3000...i think i lost a tiny stumble through slow acceleration which was there before. Maybe it's because it's colder out today, maybe it's in my head...anyway, got a great feeling to have tackled another little item and learned along the way. (and it's great to see that the computer is working as it should.)

[wreckah]

now let's see what mpg's i will get, not that i care

[groovydude]

Jan, I've been having the exact same symptoms with my car since I refurbished my CIS. The thing is, about once in every 12 starts or so it starts up perfectly. And before the rebuild I did not have this issue (just very high idle due to a blown air box), so I don't think it's the WUR. All my components seem to check out perfectly, all my pressures are within spec. My o2 sensor is new and connected. My gut tells me that this is an electrical issue. The wiring on these cars is old. I noticed that there was a fair smount of corrosion on the terminals of my WUR. That connection shouldn't effect the cold start idle, but perhaps one of the others might? Just a thought.

I've been living with it. 30 seconds of slop is tolerable, since the joy of driving isn't effected, but it would be nice to resolve this issue. I'll hopefully have some time in the next couple of weeks to play around, and I'll post if I find anything interesting!

[groovydude]

Hey Jan,

I may have made some progress, check this out:

'82 CIS cold start issue

Try it out and let me know you get the same results.

Groovy

[wreckah]

hi groovy, yeps, 20 seconds of spluttering is not that hard to live with, especially since i need like a minute to get out of my garage, open the gate, close the gate, hug the dog, etc so by the time i'm out in the street the car runs great...

i'll try your throttle tap to see if it catches more quickly. We're still having very cold nights here (almost 0°C) and morning starts mean 5 seconds cranking before she catches.