AAR opening question

[Johner]

I've been having cold start problems on my 1983 911sc and am checking out the CIS components. I pulled the hose on the AAR to check opening. The opening seemed to be less than an eighth of the area (see bad quality picture below) and air temp is about 10C or 50f. I'll check warm closing later, but does this seem correct for cold opening?

Thanks,

John

[Dr J]

Looks ok. In my experience with a few of these, they don't open all the way or even half way. Otherwise idle speed cold would be way too high.

Ultimately, if you are happy with the idle speed when cold, you are good to go.

[Bob Kontak]

Originally Posted by Dr J

Looks ok. In my experience with a few of these, they don't open all the way or even half way.

+1

On my US version, I would say a quarter of the area of the circle (from memory).

[boyt911sc]

John,

Are you sure you have the correct AAR for your '83 SC? Could you post the Bosch ID number on your AAR? Thanks.

Tony

[Johner]

Hi Tony

It looks like 0280140226 stamped on housing. It's a 1983 Euro SC.

The reason I'm checking AAR is that car will start, idle very low, revs climb to about 800rpm then die abruptly. Plugs start to foul after a few starting attempts.

Thanks

[Bob Kontak]

Originally Posted by Johner

Hi Tony

It looks like 0280140226 stamped on housing. It's a 1983 Euro SC.

The reason I'm checking AAR is that car will start, idle very low, revs climb to about 800rpm then die abruptly. Plugs start to foul after a few starting attempts.

Thanks

There are four places the factory allows air to enter. Designed false air can be another term.

None of them normally engage during warm operation except the thick dime sized screw on the driver's side of the throttle body. Idle air bypass.

If you are super rich/squeezed for air, you should be able to back off the idle air bypass and get a touch better performance on start up.

This is not the solution, just a step to confirm if your present AF ratio is an issue.

[Johner]

I spent a bit of time testing AAR. Tested 21 ohms across pins and verified power to connector. Reconnected and powered up for 2 minutes and no noticeable change in opening size. I think next step should be to remove and do freezer test. Assuming that doesn't change opening I guess I should plan on opening it up and cleaning it all up. Does this sound like the right way to go? Any tips for removing AAR and servicing it? I was just planning on cleaning the internal mechanism as a first step. I think I'd rather do this and make sure it's all running ok before playing with idle or fuel

[gazzerr]

You can also chuck in the oven at 185 F or so and verify that it closes. Mine closes too fast before my engine is ready so it wants to stall unless I drive off and warm it that way before it starts to close. It should take a good 4 or 5 mins before it completely closes.

21 ohms I think from memory is pretty close to OK. Tony and others will know.

Good starting point is to start with your fuel pressures and then do a false air test and look for vacuum leaks. Search for the "CIS for Dummies" thread. It's the go to on this forum.

G.

[Bob Kontak]

Originally Posted by Johner

I think I'd rather do this and make sure it's all running ok before playing with idle or fuel

Playing with idle is little. Playing with fuel is big.

Two minutes is not enough time to seal AAR.

Take it off with an allen wrench. Put it in the freezer. Is it open? Take a better picture.

Heat oven to 125. Stick it in there for ten minutes. Does it close? Edit: I see gazzer's 185f. It's been a while..............

[Johner]

Thamks for the help. I ran the power to AAR for 6 mins this time and it closed nearly completely. I have CIS test kit on order so will test pressures next. Will probably leave AAR as is for now until I've tested other parts of the system. Will try adjusting the idle though

[tirwin]

Originally Posted by Johner

Hi Tony

It looks like 0280140226 stamped on housing. It's a 1983 Euro SC.

The reason I'm checking AAR is that car will start, idle very low, revs climb to about 800rpm then die abruptly. Plugs start to foul after a few starting attempts.

Thanks

Roughly how long are we talking from crank to when it cuts off?

[Johner]

It just takes a few seconds to get to 800rpm before dying

[T77911S]

all the AAR does is give it a little extra air when starting and raise the idle once it starts.
spray some carb cleaner in the AAR and see if that frees it up.


how does it run once warm?
set the idle when warm, don't set it for a good idle when cold, that's the job of the AAR after the AAR is fixed.
if it idles at the proper RPM warm and the AAR is stuck open someone has already adjusted the idle down to compensate for the AAR being stuck open. if it has been this way since you bought it and you are now having starting issues you have another problem. either air leaks or CP/WUR problems. a common WUR issue is a dirty inlet screen, that will raise the CP and lean it out.

[diy83sc]

I had an AAR that wouldn't close to its normal position until the engine was hot. A slight tap with the handle of a hammer helped release it. I tried spraying lube in it but that didn't seem to help. Eventually got a new one. You might try tapping it after the first stall to see if it was "stuck".

[Johner]

I tried a bit of wd40 in the aar slide and it seemed to open a bit further when cold. The AAR did close almost fully on battery power after about 6 minutes. Once started and warm the car seems to run well, the only issue seems to be that sometimes the idle hangs at 1400ish rather than dropping to ~950.

I'll check fuel pressures this weekend to confirm WUR operation, then adjust mixture if everything else checks out.

Thanks for the help and tips

[gazzerr]

That's great. It should idle up like that when it's stone old then slowly run down to ~950. Don't mess with the mixture until you know you are free of vacuum leaks, the pressures are good and you know the timing is correct. Once you can confirm that there are no vacuum leaks, your pressures are good and your timing is right then it might simply just need an adjustment on the idle bypass when at operating temp. These systems get messed with like crazy so you have to confirm a baseline.

If it's hanging when hot after you give it a rev or backing off the throttle it might be the deceleration valve sticking open for too long. Lots of threads on that. You can disconnect the little vacuum hose on the gold "flying saucer" and plug the hose to test. I had issues with mine. I just couldn't get the idle to stay at 950 when the motor was warm. I replaced with a known good one and it appeared to be solved for me.