Idle surge when warm

[MikeRick]

Hello Gentlemen and Ladies,

1978 911SC. Car starts with a bit of cranking. New starter. Once running, everything is good. High idle for a bit and then settles down to 900 rpm. After driving for a good hour or so, temp around 180, idle starts to surge. If I don't feather the throttle, it will eventually stall. I've been searching the forums and have seen some similar posts, but I seem to have a unique issue. I have some bathroom plumbing on my AAR(?) Possibly a replacement for the AAV? I'm my phone, so not sure how to post a pic, but there is a plumbing valve (the nice, clear, oval handled valve from under the sink and toilet) and some 1/2" copper tubing.

[MikeRick]

[mike gilbert]

Sounds like your warm up regulator is acting up. Mine did the same thing except it would run fine till I killed it after being warm...The main culprit could be your fuel tank is rusting but maybe not, you need a set of CIS gauges to really diagnose these kind of problems..you may can get lucky and just make an adjustment on the WUR..Its not that hard of a procedure. You can check the condition of your tank by removing the fuel filter and cutting it in half to see if its has rust gunk, have you replaced the fuel pump anytime soon? Im sure these kind of issues are very common.

[MikeRick]

Thanks for the reply.

Fuel pump was changed last year, along with the fuel filter. I was beginning to have these issues last summer, on a road trip in BC. High altitude and very hot days. I'm really more interested in the PO's plumbing rig. Would love some insight into that. I'm wondering if I can close it off altogether.

[boyt911sc]

Originally Posted by MikeRick

Mike,

Who ever did this fix had a very clever idea. Unfortunately, the valve does not work unless you manually open it during the warm-up phase. Do yourself a favor and test your AAR (auxiliary air regulator). This subject is well discussed in this forum and should have plenty of correct information to follow. I have that exact valve installed in my bidet. Keep us posted.

Tony

[MikeRick]

Thanks Tony. That's kind of what I figured. For three years, I never had any troubles, summer or winter, (Canadian winters), but last summer, things went awry. I'll get on checking the AAR.

[targa80]

have you considered getting rid of the PO jerry rig and getting the actual part that should be there?

[MikeRick]

Yes, I have. That was part of my original question. Is that taking the place of the AAV? Or do you think that is a fix for a malfunctioning AAR?

[targa80]

Here are two views of my 80SC engine, to give you an idea of what components might be missing on your engine. I do not know what the specific difference between the 78SC and 80 SC is except the block diagram of the vacuum lines shows the 80SC has the deceleration valve along with the auxiliary air valve. I believe they are the two round anodized cans in the pictures.

[boyt911sc]

Originally Posted by targa80

Here are two views of my 80SC engine, to give you an idea of what components might be missing on your engine. I do not know what the specific difference between the 78SC and 80 SC is except the block diagram of the vacuum lines shows the 80SC has the deceleration valve along with the auxiliary air valve. I believe they are the two round anodized cans in the pictures.

Pat,

The '80-'83 SC's have three (3) to one (1) aluminum tube contraption compared to '78-'79 SC's two (2) to one (1). The difference is for the decel valve. These two (2) groups of SC models have different type of decel valves.

Tony

[Bob Kontak]

Originally Posted by targa80

have you considered getting rid of the PO jerry rig and getting the actual part that should be there?

Oh, ye of little faith.

First off it's jerry-built. Not jerry-rigged. Sheesh.

Jerry-built means it's trash. Jury-rigged means a MgGiver type implement. Great for bridging a problem.

That is what this is. Not pretty but it worked - well, I think.

Mike, do you/have you ever touch the toilet water valve? I am thinking the installer used this as a "choke" for cold starts.

I bet it is/has been screwed in all the way.

[MikeRick]

I haven't touched it, until now. All the way in, kills the engine. Wide open, seems fine...ish.

[911SauCy]

Your toilet is running...

How bout you consider something basic, like your car is possibly running too rich.

Takes a while to crank, hunting idle, stalls sometimes... just a thought

[MikeRick]

That's what I've been working on. Picked up an LM-2. Just unsure if I should be turning off the toilet before checking mixture.

[boyt911sc]

Originally Posted by MikeRick

That's what I've been working on. Picked up an LM-2. Just unsure if I should be turning off the toilet before checking mixture.

MikeRick,

You need to determine whether the AAR (auxiliary air regulator) is good or defective. A simple test to determine its condition is to cool the AAR. Fifteen mins. inside your refrigerator would cool down or let sit at room temperature for a while. The valve should be open.

The second part of the test is heating. Apply 12-volts to the plug and the slide valve would close (3 - 4 mins.). Or place it in the oven @170°F for 5 mins. and observe the opening. In both tests, the valve should be fully close.

BTW, the normal opening of the valve is somewhat between 1/4 to 1/3. It does not fully open as what most people expected it to be. Keep us posted.

Tony

[MikeRick]

I really appreciate all the responses! These forums are amazing. Just needed to say that.

Tony, I will get on that shortly. What is your take on the bidet plumbing? "AAV"? Please excuse my ignorance. I was raised on Chevys. Thankfully, I saw the light.

[MikeRick]

Ok. Never got around to removing the AAR and toilet. Did a bit of deduction, with adjusting said toilet. Went with what Bob had said about the toilet being closed. With it open, and at a reasonable idle, at running temp, there was no change in idle when the oil cap was removed. Worked on slowly closing off the toilet and then adjusting mixture. With the toilet open just a hair, mixture fluctuating a tad, (LM-2 sensor on exhaust. Unable to get the plug out to properly place the sensor), idle had been very steady. Started right up this chilly morning. Good idle. No fluctuations. Hope I went about things the right way. Going to order an AAR and AAV, when funds allow. Get rid of my toilet and make this right. It's scary digging into this thing. Seems I'm always seeing things that the PO did, that make me scratch my head.

[911SauCy]

Originally Posted by MikeRick

Ok. Never got around to removing the AAR and toilet. Did a bit of deduction, with adjusting said toilet. Went with what Bob had said about the toilet being closed. With it open, and at a reasonable idle, at running temp, there was no change in idle when the oil cap was removed. Worked on slowly closing off the toilet and then adjusting mixture. With the toilet open just a hair, mixture fluctuating a tad, (LM-2 sensor on exhaust. Unable to get the plug out to properly place the sensor), idle had been very steady. Started right up this chilly morning. Good idle. No fluctuations. Hope I went about things the right way. Going to order an AAR and AAV, when funds allow. Get rid of my toilet and make this right. It's scary digging into this thing. Seems I'm always seeing things that the PO did, that make me scratch my head.

I'm starting to believe myself

Toilet was running and you needed a mixture adjustment...

[MikeRick]

So....weather has cooled. After getting things running properly, idle started acting up again. Car is starting fine. Goes to a good high idle for warm up and then drops down to +-900 rpm. After reaching running temp, or close to, it starts surging and eventually will stall. Yesterday, turned the toilet all the way off and set mixture and idle. Everything was perfect. On the drive home, (about 30 Kms), the car ran great. Got home, idle remained steady. After sitting for four hours or so, started her up. No problems. Nice idle and then down to running idle. Drove a couple of Kms and the surging started again. It would seem as though some thing is changing.