328 high idle... again. Will a K-Jetronic expert be able to help?

Did you measure the resistance across the AAV connector ? it should be about 22 ohms. Also did you remove the AAV and check to see that it closes when warm ? Many stick open causing excess air flow thus increasing idle speed. If it's sticking , clean with carb cleaner and spray a little wd-40 in there to help it slide closed when warm.
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The first test to rule the AAV in or out as the problem is to just physically pinch one of the large rubber air lines that mate to the AAV closed (to block any airflow into the engine):

if the warm idle drops, something is bad with the AAV system.

if the warm idle stays the same (high), the problem isn't the AAV.

When you say "Idle screw - I can twirl all I want since the throttle position is nowhere near it." -- do you mean the throttle plate rest screw or the air bypass screw?

 

NO, the throttle should NOT be touching the manifold. I have a 308qv, which should be similar (I think) and it's 1/4 inch from touching the manifold.
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No problem with your English and the pictures do help. That small black plastic piece (in the yellow circle) is actually supposed to prevent you from turning the throttle position adjustment screw, but perhaps it's been damaged/stripped out over the years (if you can turn it now freely).

I do think that it is very abnormal that that linkage piece is hitting the intake plenum. I believe that there should be a small round bushing on the pin that I've labeled in the jpeg, but maybe another 308QV/328 owner could comment (edit: Steve's post shows the bushing). If the pin seems much too small for the curved slot, that might be another clue that a bushing is missing.

I think you should focus on the linkage rather than the AAV, but do that quicky test blocking one of the AAV air lines and you'll know if it's involved or not.
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Where, exactly, is the AAV located?

Pics, diagram, description...anything would be appreciated. Thanks.

 

Push the exposed part of the wire on the connector inward -- then pull apart.

It looks like someone has just backed out the throttle position adjustment screw way out. It doesn't contact the linkage arm very much (like less than 1/2 a turn). The pin being "bottomed out" in the slot as you show in your jpeg is not correct -- should be more like spiderseeker's jpeg.

My guess would be that your air bypass screw is opened too much and to compensate they (wrongly) backed off the throttle position adjustment screw.

 

Sounds like your water temp is right to me - its the same as mine. Car should run at that temp all day in any weather unless you get into traffic where the temp will climb to the middle & the fans will cut in. The car is not running cold.

See above - the car is not running cold so I think you are on a red herring with the AAV

Good - but is the throttle pedal linkage sticking/stuck? Is there any slack at the engine end of the cable ? It should not be tight & if it is then maybe its your pedal. If its not then you can pretty much rule out the linkage

OK, but is the butterfly in the throttle body closing properly all the way? push on the linkage gently to see if you can "help" it to close. If you can then take the TB off and clean it. I cleaned mine a year or two back because it was very dirty inside & the butterfly wasn't closing all the way (causes air to leak in which causes the revs to rise)

Fine but what about the Air idle adjuster?

see part 23 in the picture below - make a note of its current position & then turn this & see what happens. You should be able to do this by hand (you might need a cloth if its hot!) Otherwise I think its an 18mm wrench. This is actually what you should use to adjust the idle. You set the idle by using this and the idle screw on the cable. Its hard to describe but basically the idle screw on the cable should be just engaged and then you do the rest with the Air Idle screw. I find my car idles best at just over 1000 rpm. If I set it to any less than this then it "hunts" a bit in the period after the AAV has stopped raising the revs & before the thing is properly warm.

Obviously you can only set the idle accurately on a warm engine !

I believe its basically the same as used on a bunch of Mercs - but from your description I doubt the Kjet is your problem. High idle is more likely just because the engine is getting too much air even when the throttle is closed. The KJet will then just feed it the fuel it wants. I think the root of your problem is too much air, not too much fuel

So either your throttle is stuck open slightly (so look at the linkage & cable and make sure the butterfly is closing properly in the throttle body) or your Air idle screw needs adjusting or you have a leak somewhere around the Throttle body, plenum or inlet manifold - can you hear anything?

I believe it is unique

Excessive clutch wear probably!

Good luck with finding the thing - please let us know how you get on.
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Its specifically for adjusting the idle & has nothing to do with the mixture. All it does is to let air into the engine which, in turn, pulls in fuel at the prescribed rate.

For reference, there is very little you can do to adjust the mixture on the Kjet beyond the idle mixture - there is an idle mixture adjuster screw on the main Kjet unit (which only adjusts the idle mixture) & that's about it. The Kjet basically works or it doesn't! To keep it healthy & clean its worth putting a bottle of injector cleaner in the tank every 6 months or so.

The "big nut" is called the bypass valve because it lets air bypass the throttle butterfly!

As 91tr said, sort out the idle screw on the linkage/cable & then adjust with the Air idle/bypass valve. As per my previous post, take up a little bit of slack on the throttle with the adjuster screw on the mechanism & then sort out the bypass valve. You might want to screw the Bypass valve down a bit first to drop the revs before you start working on the throttle mechanism/idle adjuster screw.

Good luck

I.

 

I read the thread... and I too think you have too much air... I just had the same thing happen on my 86 328... It was caused by a collapsing hose going from the AAV to the cold start injector... I replaced the hose, and new clamps... and it seems better now..

I would look for an air leak.. I used a big clamp on each hose to see what the reaction of the engine was... so this is easy...

also the trottle stop is not supposed to touch the intake .... your ajdustor screw should be used to set the proper throttle setting so you get full throttle... this is easy to do, but complicated by the engine cover...

I would reccomned checking for AIR LEAKS ... old rubber hoses crack eventually...and are cheap to replace.

Tom

 

Hi Poleapart,

Suggestions above are excellent. However, a few other possibilities:

* If your WUR is sticking (and fuel injection control pressure is low) the mixture will be "rich" and thus idle a bit faster.
* Does the FI temperature sensor switch on the expansion tank switch to "open/hot" position as the car warms (changing duty cycle on the frequency valve, which actually "leans" the mixture as the engine warms)? If it is sticking in the "cold/continuous" position the mixture will remain "rich".

Best,

Carl

 

Both Spirot's & Carlrose's suggestions are good ones - if its not simply a question of setting the idle correctly then follow their ideas.

Come to think of it, unless someone has been messing with your engine there's no good reason that the idle should be off in the first place - so perhaps an air leak or a sticky WUR are the most likely culprits.

I.

 

Go back and look at the pictures in post #8. The part that is hitting the intake plenum is the problem, I think. If that was able to rotate a little more forward it would let the throttle plate relax a bit more and stop on the idle adjustment screw. I don't know how to get more space in between there - maybe a thicker gasket between the throttle body and intake plenum? - but I really think that is the root of your trouble.

 

did the problem just occur, as in all was fine until? or is this an ongoing issue? if it just showed up I'd look for a vacuum leak, a leak will also cause a lean condition that is not good.

your throttle settings do need to be adjusted, but until you find the leak source it's will be pointless. if it is the throttle setting being off then adjust that, the WSM explains exactly how to sit it right, you'll need a vacuum gauge that can read in low pressures, a used medical one works great and are usually calibrated very finely.

the air bypass screw under the throttle needs to be closed up fully then the throttle plate screw is adjusted to get the readings within range, once they are as close as you can get them the bypass screw is adjusted out to get the settings to spec. a common mistake is to adjust the bypass screw, it should be left alone unless absolutely needed.

 

that wouldn't work, the throttle plate assembly is cam driven, rotating the cam towards the plenum will not move the plate any further as it is at its full range, rotating it towards the back of the car will move the cam and then rotate the throttle plate open. the adjustment screw holds the plate open just enough to set idle, since it's not contacting the assembly the throttle plate is fully closed.

the throttle cable also has slack adjustment, it's where the cable meets the throttle assembly, figure 7 above.

 

Put my AAV in the oven/freezer- worked normally. Checked elec resistance- worked normally. Car still idled irratically. So... with the car (308QV) running, warm and idling I tapped the AAV with a screwdriver...and lo and behold the idle dropped to normal. AAV was still sticking. Need new AAV.

 

I really do think your high idle could be false air in the system, BUT... with your throttle flange hitting the plenum and the throttle stop totally out of Adjustment... its hard to say... if you turn the throttle stop adjusting screw down your gonna increase the RPM...if you then adjust the bypass screw... then you can lower the rpm ... with out changing CO or idle mixture... which you just dont want to do unless you have all the analysis equiment...

I would adjust the throttle stop so that you are NOT hitting the plenum in any event... and ensure you have full throttle available... Most likely your idle will increase substantially...

then bring the idle down with the bypass screw, and see it that helps... if not or it only does a small adjustment then I'm pretty certain you have an air leak... they are a ***** to figure out...

Remember you can test the AAV by warming up the car and clamping the hoses to see if you reduce the idle... if that happens then most likely you have an air leak... P.S. you need to do all this with a warm engine around 195 * F.... so wear some heat insulating gloves ... it gets hot down there.

 

OK, he seems to have this solved, so this is just for my own curiousity:

How can you tell that the throttle plate is fully closed? I read the space between the idle screw and the throttle arm to indicate that the throttle is NOT all the way closed and that the cam was holding it open because it couldn't relax anymore. It just seems like too much of a coincidence that the throttle would be in the all the way closed position at the same time that the cam is up against the plenum.

 

having taken mine completely apart I've been thru the reassembly and set-up. the throttle plate will be fully closed when the screw is no longer holding it ajar, the cam slot has both extremes from closed to open.

with the pictured setup the bypass screw is setting the idle and it should not be, the throttle plate should be setting the idle and only when due to machine tolerances where the throttle plate can not set it correctly should the bypass be opened. it's explained in the WSM.