ENGINE REVS WHEN IN PARK AND NEUTRAL

[JAYAUCK25]

I JUST PURCHASED A 1974 450 SEL,  WHENEVER THE CAR IS IN PARK OR NEUTRAL THE ENGINE REVS .... AND IT SEEMS LIKE IT'S IDLING TOO HIGH ALSO...  I'M NOT FAMILIAR WITH THESE CARS AT ALL SO ALL AND ANY HELP WITH BE GREATLY APPRECIATED!!!

[scraf]

Mine does too, think it's normal, as I've read that you can avoid overheating in traffic jams by putting the car in neutral, making the water pump run faster.

[Bandolero]

It should idle at about 600 - 700 RPM in park once it's warmed up to operating temperature. If it is too high you can adjust the plastic screw  on the air-slide.

[WGB]

1) Tell us what year and market your car was manufactured for and  I will give you the specs for the correct idle speed.

2) If you have airconditioning and the system is not connected or has run out of gas the idle speed will increase significantly when it expects the compressor to cut in. If this is the case you wil have to either fix the aircon or disconnect the idle vacuum advance/retard a/c control.

Bill

[oscar]

Congrats on the purchase Jay.  You've got d-jetronic fuel injection on your engine and this high idling is only a problem if it's doing it whilst the engine is fully warmed up.  When cold it's normal that it should rev up a bit without touching the accelerator and without the engine being under load.  

But when it's fully warmed up, the auxillary air valve should be closed and the revs approx 700 (reply to WGB to get exact rpm, i can't remember off hand).  If it's a lot higher you should do what bandolero says about screwing down that warm engine idle adjustment screw except the screw may be metal on your car.  Either way, looking at the pic below, the auxillary air valve is the tall alloy thing in the middle of the pic with large black hoses attached.  Looking at the hose at the left that splits into a "Y", one leg goes to the auxillary air valve and the other leg goes to the warm engine idle adjustment screw which sits aft and to the right of the auxillary air valve if facing the engine.

I found a second pic at bottom there that shows the screw after hoses are removed.

If you have problems with poor idling whilst cold after resetting the warm engine idle adjustment screw or the adjustment has little effect on warm engine revs at idle, it's likely that your auxillary air valve is operating poorly.  It'll need a good clean out or replacement.  But try the screw first and see how you go.

[JAYAUCK25]

Thanks for all the info,  but I am not sure that I explained what is happening clearly.  It does idle high, but what concerns me more is that it revs itself between about 1000 and 2200 rpm's when in neutral or park.  It does idle at about 1100 rpm's when in drive.   I did adjust the screw and that seemed to help, but  I think I will try cleaning  the valve also.

[oscar]

but I am not sure that I explained what is happening clearly.  It does idle high, but what concerns me more is that it revs itself between about 1000 and 2200 rpm's when in neutral or park. 

You mean if you plotted engine revs on a time graph for the above it would look like a sine wave?? Have a look at 13B's 450 in the video below.  This up and down revving is what I thought you were referring to.  If this is what yours is doing then the restriction in the hose to the AAV should eliminate it.

http://au.youtube.com/watch?v=9a4WiAk9Ass&feature=user

If at all your suspect about the AAV fully closing there's no harm in soaking the AAV in WD40 or INOX over night then put it through a number of heating cycles in hot then cold water to get the valve moving and washing out any crud in there with the penetrant oil.  It's worth doing so you can view if the valve is closing.   You'll probably find adjustment of the idle screw is needed again afterwards.  As it is 1100rpm's in Drive is too high for a warm idle. (assuming that was at warm idle).  If the warm idle screw doesn't bring it down then it would be fair to say that the AAV is staying open longer than it should or it is stuck open, not fully closing.

[oscar]

Oh fudge!!! Hang on Jay, I just realised my first post hasn't got the remedy and explanation in it.  I typed it in yesterday but must have pasted over it whilst adding the second pic.  I've completely deleted a paragraph or two.  Sorry about that, no wonder it doesn't make sense.

Here's what's supposed to be in my first post.

The fix is this - you need to put a restriction in the leg of the "y" hose that goes to the Auxillary Air Valve.  I used 7.5mm fuel injector hose cut to about 2 inches and stuck it in that part of the hose.  Other methods include cutting the threaded part off a spark plug and shoving that cylinder in the hose.  Also you can tap down the top of the AAV.  I tried this too but only got it to move a few mm and I was scared about hitting it harder in case I broke something.

What is happening is that during a cold idle, the air going past the idle screw and the extra air past the AAV causes the engine to rev up.  At a certain point the ECU kicks in to stop the revs running away.  It intervenes by cutting off the current to the injectors.  With no fuel, the revs drop to a low point whereby the ECU restarts the signals to the injectors and it starts to rev up again.

Hope that helps.

[JAYAUCK25]

I will try this... you've been a great help.  I'll let you know how it comes out!!! 

[JAYAUCK25]

I took off the aav and i sacrificed the hose that goes from it to the idle screw, any one have any suggestions on where to buy this hose!  I will also need other hoses too, most seem brittle on the engine.

[oscar]

Have a look here, a lot of people on the forum all over use this mob.

Link

[JAYAUCK25]

Thanks Oscar!!  I cleaned out the aav and it worked great.  I'm sure it will be even better once I receive the hoses that I tore up!  I have just started renovating this car so I'm sure I will have lots of questions in the future. 

[450se1979]

I seem to be having the same problem on a K-Jet engine; is there a different fix for the K-Jet?
The fluctuations in at idle speed are appr 300rpms, but are very consistent...


Jeen

[TJ 450]

I seem to be having the same problem on a K-Jet engine; is there a different fix for the K-Jet?
The fluctuations in at idle speed are appr 300rpms, but are very consistent...


Jeen

Is it actually oscillating, or is it more like a missfiring cylinder? Fluctuating, hunting or oscillating idle speeds are usually associated with electronic systems.

I stand to be corrected, but I don't think the K-Jet system is fundamentally capable of such a "loop mode", in its first iteration.

If yours is actually a K-Jet system, I would be inclined to think that you might have an ignition or fuel mixture related issues. If you have an idle speed that is fast across the board, you might have an air leak somewhere. Placing a restriction in the AAV hose will certainly help if it remains partially open when it should be closed, but compensation must be addressed with the base idle screw and it will be less than perfect.

[virtualgarage]

The post reminds me about my X- '79 450SEL.  It is not D-jet but same high engine rev on park or natural. It happened mostly on cold weather or engine.  I lubricated all joints on linkages from accelerated paddle to throttle plate. The problem was gone before I toasted it. Don't forget to check the spring on the throttle plate.

HTH

Rocky
'79 6.9
'69 6.3
'57 220S