1978 450 SEL High Idle problems- 2000 rpms

[skatinblind815]

I came on this website in the first place because I bought a red 1978 450 SEL from a guy named Mark. Im pretty sure I bought it from the guy Mark who started this thread earlier  (http://forum.w116.org/mechanicals/1978-450-sel-high-idle-2000-rpm/.)

I've tried almost everything i Read in that thread. My car did just have the engine rebuilt and it runs very well, except for the high idle.
So I since ive had the car, it still has this problems. While in park, It currently idles at 1700-2000 rpms and occasionally goes a little lower. I took the advice of this website and switched to premium unleaded gas only. I've checked all of the vacuum lines that I can find in and around the engine compartment. Ive adjusted the idle control knob and that only raises or lower the idle very slightly. Ithink that there is some kind of vacuum leak somewhere but I could be mistaken. I need some good advice on anwhat it could be. I also checked the throttle linkage to see if it was stuck but it isnt. Whats the next step, gentlemen?

[oscar]

Did you check the last two links by koan in that thread.  Particularly his first one or here Link
because barring a major vac leak or idle screw poorly adjusted I'd be pointing my finger at the auxillary air valve being stuck open.

Does the idle stay this high after driving for a while and warming it up?

[skatinblind815]

After warming up and driving, the idle does stay high. I have a feeling that you guys are right about the auxilary air valve. Is there a way to test this piece?Koan posted this picture of it. (http://gallery.w116.org/v/garage/koan/Miscelaneious/DCP_3476.JPG/) The only part of that that i have looked at is the part with the blue piece that comes off. How would i go about testing if the part in the picture is functioning correctly?

[thysonsacclaim]

The only way to test it that I know of, if I understand your question correctly, is to remove it and place it in boiling hot water.

It should close all the way or nearly all the way after a few minutes in hot water.

Then you can cool it off and drop it in an ice bath and place it in the fridge or freezer for a few minutes. Don't let the water freeze, though. Just enough to help keep the temp cool.

It should be open when cool.

[skatinblind815]

OKay thanks, I a while ago I tried that with my volvo cold start valve. The part I should test this on is the part in this pic http://gallery.w116.org/v/garage/koan/Miscelaneious/DCP_3476.JPG/ that has the blue part on it that is removed with the two allen bolts? Is that what you mean?

[thysonsacclaim]

Actually, I think the part with the blue piece is the part that controls the idle, no?

The AAV is conected to this if that is the case. I think it is the unit to the right. I have a 74 450; they use a different valve because the injection system is different.

I am on a phone, so it's a bit hard for me to insert links to other posts. However, if you search for posts made by me, you will see one called "a bit stumped here."

In that post there is a pic somewhere of the AAV which is used for your k-jet system. It is the pic of the two sitting in water.

Cheers

[koan]

The piece with the blue bit is the cold start valve, it adds a extra fuel to aid starting in cold weather.

The Auxilary Air Valve is the thing at the right of the picture with the brass coloured bit at the bottom.

There's a better picture of it here.

http://gallery.w116.org/v/garage/koan/Miscelaneious/DCP_3479.JPG/

koan

[skatinblind815]

Thanks Koan. Okay so I'm taking the AAV through cold and warm cycles right now Thysonss. When i removed it, a ton of antifreeze came out but I plugged it up. The AAV has a sort of nipple looking thing that when its connected is IN the hot fluid so from that i have deducted that it is heat sensitive or something. So now i have a few questions. Would the cause of the high idle be that the AAV is stuck open or closed? If it was to work properly what would it be doing in the system? I'm a MB newby please explain 
p.s. this website is AWESOME, thanks for the help people

[koan]

So now i have a few questions. Would the cause of the high idle be that the AAV is stuck open or closed? If it was to work properly what would it be doing in the system? I'm a MB newby please explain 

Modern cars have electronic means of monitoring and correcting engine idle speed as the engine warms up by adjusting the opening a valve that allows air into the engine around the throttle plate.

Our aging vehicles have a purely mechanical system, the Auxiliary Air Valve. The bottom of the AAV contains wax with a low melting point, around 75 degree C. Waxes expand when they melt (a lot more than liquids and solids), the cooling system water heats the wax in the AAV as the engine warms up. The resulting expansion  of the wax moves a piston that blocks off the air flow through the valve reducing engine

The valve should be pretty much wide open cold and fully closes when above 80 or so degrees C.

Over time the valves get gummed up and also not to close fully which I'm guessing is due to loss of the wax.

koan 

[skatinblind815]

damn i love this website..
So I think my AAV works. But one question, when the engine it hot, it should be fully closed right?  When I take it out and test it in some really hot water It should close completely and I shouldn't be able to blow ANY air through it right? Right now, it gets hot and I can see that it is moving inside, but i dont know if its a complete seal because I can still blow a small amount of air through it. But it definitly didnt do this yesterday because I've soaked it in some penetrating oil and cleaner type liquid. So if the AAV is closed, NO air should be moving through it?

[oscar]

When closed it should be air tight.  If there was a slight, tiny amount of air still going through it I wouldn't be too concerned but you have to think you'll have around 15psi plus vacuum operating on the other side which is more than you can blow or suck through it.  If I have my car running hot and take the inlet hose off the AAV and put my finger on the intake part, it's still sucking air in.  It's not ideal but it was better than before my first clean attempt and at least things are constant.  I've planned for a couple of years on doing it again with carb cleaner or kerosene.  Just haven't been bothered yet.

Our aging vehicles have a purely mechanical system, the Auxiliary Air Valve. The bottom of the AAV contains wax with a low melting point, around 75 degree C. Waxes expand when they melt (a lot more than liquids and solids), the cooling system water heats the wax in the AAV as the engine warms up. The resulting expansion  of the wax moves a piston that blocks off the air flow through the valve reducing engine

Seriously, wax?!  I've never heard that before koan, I'm super impressed.  I thought there was some bimetallic heating element in there.  A loss of wax would explain an awful lot.  Eg, another fix I was told about was to tap the top of the AAV down with a hammer.  Not really recommended for risk of breakage, but I did try it which reduced the closing gap.  A loss of wax or change of wax characteristics if possible would explain why they don't close too well all the time despite cleaning attempts. 

[skatinblind815]

Whats up guys. I've been workin on the 450 for the last couple days so here is where I'm at now. I messed with the auxiliary air valve and got it to open and close almost all the way but it still wont fully close. Thinking about getting a replacement, where should I look for it? Also rotated the distributor to the and change the timing, and it lowered the idle speed but in the following test drive there was no real power. I put it back into the original position. I also made another discovery. My vaccuum advance was completely seized! I got it loose and working though.

Where should I look now for the cause of my perpetually high idle?
someone please help me!

[Big_Richard]

how far open is the auxiliary air valve remaining open at regular engine running temperature?

[skatinblind815]

Major Tom,
it is staying open about one centimeter. Is this a problem?

[s class]

one centimeter is huge.  it needs to CLOSE.