What is your SL's Idle Speed?

7839 Views 27 Replies 9 Participants Last post by Blu-spot, Jun 9, 2008

MBGraham

Discussion Starter · Oct 26, 2007

What is the idle speed on your 107 SL when in P or N?

Is this with idle screw all way in?

What happens to speed if you screw it all the way in?

(Idle screw is located near the distributor and upper radiator hose. It has two large vacuum hoses (3/4 or so) and a plug with two wires. The screw is about 3/8" diam with large screwdriver slot)

Year and model?

My '72 350SL idles at about 1100rpm in Park when cold and about 900rpm when warm. In Drive, it is about 700 rpm. No vacuum leaks that I can find. Idle screw is all the way in - no adjustment left.

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ScottinSoCal

· #2 · Oct 26, 2007

w107w123w210 said:
My '72 350SL idles at about 1100rpm in Park when cold and about 900rpm when warm. In Drive, it is about 700 rpm. No vacuum leaks that I can find. Idle screw is all the way in - no adjustment left.

Your auxiliary air valve is bad or going bad and allowing too much air in for too long - probably even when it should be cut off completely.

To verify this, look at the front of the engine when it's at operating temperature and running. There's a short, L-shaped black rubber hose going from the auxiliary air valve. Disconnect it from the auxiliary air valve (your engine will race - this is normal) and put your palm across it to block it completely. Your palm, not your fingers. There's a huge amount of vacuum there that will suck your fingers right into that tube. If your engine dies or the idle goes down to the point where it's almost dead, your auxiliary air valve is shot. This is a horribly expensive little piece of nothing, and almost no place sells them. If you verify this is the cause, PM me and I can walk you through a couple of tricks to get it working again.

ussun

· #3 · Oct 26, 2007 (Edited)

Cold In P about 12.
Sorry i wouldn't move that screw even for my mom.

MC06A

· #4 · Oct 27, 2007

Usually 700 in Park and 500-550 in Drive at a traffic light.

It's been high idling lately, 1200 in Park and 900 in drive one instance. My most severe case of high idle was 3000 in Park and 1200 in Drive a few weeks ago.

MBGraham

Discussion Starter · #5 · Oct 27, 2007

ScottinSoCal said:
Your auxiliary air valve is bad or going bad and allowing too much air in for too long - probably even when it should be cut off completely.

To verify this, look at the front of the engine when it's at operating temperature and running. There's a short, L-shaped black rubber hose going from the auxiliary air valve. Disconnect it from the auxiliary air valve (your engine will race - this is normal) and put your palm across it to block it completely. Your palm, not your fingers. There's a huge amount of vacuum there that will suck your fingers right into that tube. If your engine dies or the idle goes down to the point where it's almost dead, your auxiliary air valve is shot. This is a horribly expensive little piece of nothing, and almost no place sells them. If you verify this is the cause, PM me and I can walk you through a couple of tricks to get it working again.

I will give it a try tomorrow. I read about this test before, but never checked just which hose I had to disconnect! I see from the manual (07.5-235) it is the one that goes from the supplementary air valve to the idle speed air distributor. I hope our '72 looks the same

Seeing I will have this off - what are the tricks? I heard something about spraying WD-40 into the valve or adding a restriction inside the hose?

MBGraham

Discussion Starter · #6 · Oct 27, 2007

OK - I removed the 90 deg pipe and blocked the port going to idle speed air distributor. Engine cut out completely.

I squirted a little brake cleaner into the supplementary air valve. (Not much seeing I don't know what is in there!). Because pipe came off a little too easily, I put clamps on when I put it back.

It's raining so I did not road test, but let the car come up to temperature. Idle speed really has not changed - still 900 - 1000 in P or N and drops to about 600-700 in D.

But, in D, with idle screw all the way in, it is a bit uneven in D, so I opened it up so speed in P/N is closer to 1000.

Starting to think that even if I get air valve working 100%, I will just have to open up idle screw anyway!

Why does speed drop so much when put in D? Something to do with torque converter?

ScottinSoCal

· #7 · Oct 27, 2007 (Edited)

w107w123w210 said:
Seeing I will have this off - what are the tricks? I heard something about spraying WD-40 into the valve or adding a restriction inside the hose?

The first thing to do is make sure your thermostat is working properly. My 75 had been completely gutted by some well intentioned stupid person. If that's working all right, focus on the AAV.

Don't take the hose completely off, just take the upper end off the auxiliary air valve and cover the end of the hose. The other air valve is also bolted to the engine and at running temperature it's warm enough to give yourself a nice brand on your palm. The idle should drastically reduce or the engine die completely if your problem is the AAV.

There are a couple of reasons for it to stop working. It has a sleeve inside that's supposed to slide up and down according to the temperature of the coolant water. At just below full running temperature it should be completely shut and not allow any air through. It gets grunged up and that sleeve stops sliding. To do anything about it, you're going to need a new gasket.

Auto part Fuel line Pipe Engine Suspension

Trick #1: Take a rubber mallet, or a hammer with a soft piece of wood and tap on the top of the AAV. It's just press-fit together and if the AAR gets lazy it may not close completely. This is a picture of the AAV on my car and the second ring of the top used to sit slightly higher than the body of the valve. Tapping it in forced it to be closed. On mine, that helped but didn't completely resolve the problem. Which lead me to

Trick #2: Remove it from the engine and clean the crap out of it. Spray it with carburetor cleaner over and over again until the stuff is coming out clean. Then do a thermal shock to force the thing to move. Have a pot of water on the stove at a full boil. Next to it on the kitchen counter have another bowl filled with ice water. Drop it in the boiling water and let it get completely up to temperature then fish it out and drop it in the ice water. Mine took about three cycles to make it slide freely. Try spraying more cleaner into it when it's both cold and hot, to make sure the cleaner gets everywhere. And, truth be told, I didn't use spray cleaner on it. I have a small ultrasonic cleaner and I dumped it in there. That did a lot more effective cleaning job than you'll ever get with spray cleaner. Mine was working so much better after this, but I wanted just a little bit more. So I went to

Trick #3: The lower bulb on this - the part that sits submerged in the coolant when it's installed - is filled with a waxy oil. When it gets warm it expands and pushes a rod that slides the inner sleeve shut. When it gets cold that rod slides back down and opens the sleeve. I don't know if the stuff gets tired or maybe the sleeve gets stuck and some pushes out of the bulb, whatever it is, it stops moving the sleeve all the way up. Use a large pair of pliers, or a bench vise and CAREFULLY squeeze that bulb a little bit to dent the sides. You don't want to crush it, you just want to reduce the inner volume a little bit. That took care of the final bit for me. There is, however

Trick #4: The last resort if nothing else works. I used this as a stop-gap until I got mine working right. I had a piece milled out of brass to act as a plug. In the center of the plug I had the shop drill a 4mm hole. That was my starting point, but the hole was too small. I had a good warm idle, but the cold idle was too low. So I used my drill press and made the hole slightly larger. I did this a couple of times until I got a good warm idle and cold idle.

I had the shop that made mine do two of them, and I'm pretty sure I still have the other brass plug laying around somewhere. I work in aerospace and we have machine shops who custom make things all the time. One of them did it for me as a favor and charged me a whopping $20 for the pieces. If nothing else works, let me know and I'll see if I can dig up one of the ones I had made and you can have it for your car.

Optionally, of course, you could just buy a new AAV. I found one place that sells them for $500.

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MBGraham

Discussion Starter · #8 · Oct 27, 2007 (Edited)

Thanks Scotinsocal,

I will probably try this today. I don't have gasket, but can probably make one.

I have a small ultrasonic cleaner. What fluid did you use? I suspect mine could catch fire if I used a solvent! I have only used it with a water based fluyid like Simple Green.

Any thoughts about drag from Torque Converter requiring a higher idle speed just to keep car running when in Drive?

Graham

PS: Engine temperature when hot is about 1/8" to 1/4" above the 175F mark on the gauge. Lousy gauge - no more numbers until about 250F!

Reactions: 1

MBGraham

Discussion Starter · #9 · Oct 27, 2007

Removed & Cleaned unit - first brake cleaner, then soak in kerosene bath, then multiple cleaning in ultrasonic bath using Palmolive dish washing fluid and water. Tons of crud came out. Checked in hot water bath - valve appears to close, but I needed to have a piece of hose to blow through to test. Anyway, it did not move much until I kept cleaning. May spray a little Teflon in to help things.

Old hoses were brittle, so have to get some new ones. I think I have some 3/4" HT hose somewhere that should work.

Thanks for the ideas - this may just work!

Graham

ScottinSoCal

· #10 · Oct 27, 2007

w107w123w210 said:
Any thoughts about drag from Torque Converter requiring a higher idle speed just to keep car running when in Drive?

Yes, the torque converter will bring your idle down when it's in Drive or Reverse. That's normal. My 75 idles about 800 in Park and 550 in Drive. I'd like the drive idle to be a little higher, but I don't want to go higher than 800 in park.

PS: Engine temperature when hot is about 1/8" to 1/4" above the 175F mark on the gauge. Lousy gauge - no more numbers until about 250F!

That's about normal. It sounds like your thermostat is working properly.

I worked with my AAV until the car ran properly with the idle screw about 2.5 turns from fully closed. Your car should still have adjustment left on the idle - that's the way it was designed. If it doesn't, something is wrong somewhere.

I haven't had any of these problems with my 78, it uses a different system. The 75 is a Bosch D Jetronic, just like your 72. A lot of the parts are interchangeable between the two, so we share common problems when those parts go bad.

ScottinSoCal

· #11 · Oct 27, 2007

w107w123w210 said:
I have a small ultrasonic cleaner. What fluid did you use? I suspect mine could catch fire if I used a solvent! I have only used it with a water based fluyid like Simple Green.

I used a water based solvent designed for cleaning contaminants from parts that I got from work. Your Simple Green or the dishwashing liquid you used are both good. You just need something that will cut grease.

MBGraham

Discussion Starter · #12 · Oct 28, 2007

ScottinSoCal said:
Yes, the torque converter will bring your idle down when it's in Drive or Reverse. That's normal. My 75 idles about 800 in Park and 550 in Drive. I'd like the drive idle to be a little higher, but I don't want to go higher than 800 in park.

That's about normal. It sounds like your thermostat is working properly.

I worked with my AAV until the car ran properly with the idle screw about 2.5 turns from fully closed. Your car should still have adjustment left on the idle - that's the way it was designed. If it doesn't, something is wrong somewhere.

I haven't had any of these problems with my 78, it uses a different system. The 75 is a Bosch D Jetronic, just like your 72. A lot of the parts are interchangeable between the two, so we share common problems when those parts go bad.

OK, I have the AAV back installed, but no change

It idles at about 1000 after a short run. If I do some stop start driving or let it idle for a while, temp gauge goes up a bit and idle goes down to 900rpm. So, it seems AAV does work, but perhaps does not fully close.

I happen to have a nice 90deg S/S industrial needle valve with a handwheel. I think I will install it this afternoon and try opening and closing it. If it shows AAV is leaking by, then I may try squeezing the AAV bulb as you suggested. But, I am a bit concerned about the cost of a new one if I screw it up!

ScottinSoCal

· #13 · Oct 28, 2007

w107w123w210 said:
OK, I have the AAV back installed, but no change

Eh, that sucks. Sorry.

w107w123w210 said:
If it shows AAV is leaking by, then I may try squeezing the AAV bulb as you suggested. But, I am a bit concerned about the cost of a new one if I screw it up!

I understand. But keep in mind, that little bulb may look delicate, but it's tougher than it looks. I had to squeeze pretty good to make even a little difference in it.

Oh - keep in mind I've got that line block. It worked very well as a temporary measure, and I'd have left it in if I hadn't gotten the thing working right. I don't see any reason to spend $500 when a $10 piece of brass will work just as well.

MBGraham

Discussion Starter · #14 · Oct 28, 2007

ScottinSoCal said:
Eh, that sucks. Sorry.

Not a problem - Just step one out of the way!

I understand. But keep in mind, that little bulb may look delicate, but it's tougher than it looks. I had to squeeze pretty good to make even a little difference in it.

Oh - keep in mind I've got that line block. It worked very well as a temporary measure, and I'd have left it in if I hadn't gotten the thing working right. I don't see any reason to spend $500 when a $10 piece of brass will work just as well.

I installed the needle valve. Even with it fully open, I had to open up the idle screw before the car would run! By adjusting the needle valve and the idle screw, I was able to get it to idle any speed I wanted! It actually looked OK too. Just one problem, the valve handle stuck up and hood would not close! I will post picture later.

It seems problem is with AAV. Either temperature is not quite high enough or valve is slightly off it's setting. I suspect a slightly higher coolant temperature might make the idle work. I will have to try and measure what it actually is. How the heck to I do that?

One thing struck me, is that for my valve or your disk to work, there must still be a flow of air. That would mean that the AAV does not close completely at operating temperature, it just restricts the air flow.

Another question - there is a hose that goes from the air distributor to the driver side valve cover - Seems to be pulling some vacuum and there is a check valve in the connection. How does that work? - It would seem to be a place for a potential vacuum leak.

Next step is to either squeeze bulb or add restriction. I have ability here to make a restrictor, so no need to mail one, but thanks for the offer! First want to buy some new hoses - a couple of them have cracks that I have patched up. I already replaced all the straight pieces with HD heater hose 3/4 & 1/2 " fits.

My wife does not understand why I would spend so much time just because the idle is slightly high!

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ScottinSoCal

· #15 · Oct 28, 2007

w107w123w210 said:
It seems problem is with AAV. Either temperature is not quite high enough or valve is slightly off it's setting.

I'm confident it's the AAV. It works the same way a thermostat does and thermostats eventually get tired and stop working, there's no reason this should be different.

Watch that you don't get the cold idle above 1500. There's a cutoff built in to the ECU on the Bosch D Jetronic and if the idle speed goes to 1500 with the throttle pedal up it cuts off the fuel until the rpms drop down to around 800, then kicks in the fuel again. You wind up with an engine that races like someone is fluttering the pedal.

I will have to try and measure what it actually is. How the heck to I do that?

I only worried about making sure my dash gauge was working right and to do that I borrowed a digital thermocouple from work. I wrapped the sensor cable around the sending unit and compared the two. When my dash gauge said 175, the thermocouple said 168. I figured that was close enough.

One thing struck me, is that for my valve or your disk to work, there must still be a flow of air. That would mean that the AAV does not close completely at operating temperature, it just restricts the air flow.

When I got mine working again it shut off completely, but that was with boiling water at sea level, so it was a solid 212. Maybe more if it picked up conduction heat through the bottom of the pot. I've tested a couple of times with it on the car by pulling the hose and completely plugging the end and the idle stays the same. I think mine just got lazy and was opening more and staying open longer than it was supposed to, so the plug with the hole controlled the excess air while it was open.

Another question - there is a hose that goes from the air distributor to the driver side valve cover - Seems to be pulling some vacuum and there is a check valve in the connection. How does that work? - It would seem to be a place for a potential vacuum leak.

I don't have that, but mine is a later model. I know they changed some things, because not all the parts are compatible.

Next step is to either squeeze bulb or add restriction. I have ability here to make a restrictor, so no need to mail one, but thanks for the offer!

I don't have a metal lathe and don't have the space for it if I did have one.

My wife does not understand why I would spend so much time just because the idle is slightly high!

Just tell her it's a guy thing.

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MBGraham

Discussion Starter · #16 · Oct 29, 2007

ScottinSoCal said:
Watch that you don't get the cold idle above 1500. There's a cutoff built in to the ECU on the Bosch D Jetronic and if the idle speed goes to 1500 with the throttle pedal up it cuts off the fuel until the rpms drop down to around 800, then kicks in the fuel again.

Good Point - I have seen that happen when I am messing around!

I only worried about making sure my dash gauge was working right and to do that I borrowed a digital thermocouple from work.

I had an infrared, but it failed, so took it back. Maybe I can use my wifes oven thermometer

I don't have a metal lathe and don't have the space for it if I did have one.

I don't have one eitehr but my neighbour does and he owes me!

Here is picture with valve in - I wish I could have just left it there! Might be able to if I turned it the other way.

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MBGraham

Discussion Starter · #17 · Nov 1, 2007

w107w123w210 said:
snipped

Here is picture with valve in - I wish I could have just left it there! Might be able to if I turned it the other way.

Today, I bought some penetrating oil called Releaseall. I took of the elbow hose and sprayed a good amount in. I let it sit for about 15 min and then restarted and warmed up with air-cleaner off. Still idling fast. Tried finger partly over port inside throttle inlet and it of course reduces idle speed.

I read about another Scotsman on another thread using a special tool known as a Pelty to solve this problem! Just happened to own one!

I gave the top of the AAV a few good pelts with the plastic mallet. I noticed a speed change. I kept doing it and had to open up the idle screw to keep th engine running!

I guess I dislodged the sticking piston . I now have idle screw about 1 turn open and car idles warm at ~850rpm in Park, In Drive it is about 700. Turning A/C on (It does not work) adds about 200 rpm.

Hopefully this is end of story - I did not have to pinch the bulb or use restrictions. I could do a little more cleaning but think I will leave it alone and move on to another job!

Thanks for the tips!:thumbsup:

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Digmenow

· #18 · Nov 1, 2007

4

Okay. I googled "pelty" to see the tool and came up with nothing. Is it just a plastic mallet?

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MBGraham

Discussion Starter · #19 · Nov 1, 2007 (Edited)

I found about it here:

idle hunt for 2mins only when cold 280se 71 3.5 v8?? - Page 2 - ShopForum

Pelt is quite commonly used for striking something repeatedly and I guess some Scots might use Pelty for the tool that is used [/I]! Maybe ScotinSoCal can help

That big white Pelty should do the job!

ScottinSoCal

· #20 · Nov 1, 2007

w107w123w210 said:
Maybe ScotinSoCal can help

Wrong kind of Scot.

I'm Scott. Reportedly descended from some small portion of Scottish blood, but actually named in honor of the astronaut who went up around the time I was born.

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