Bosch K-Jetronic experts chime in - high idle problem

[FCD]

My 1988 Ford Escort XR3i has the "infamous" you could say Bosch K-Jetronic system, ( better than Ford's EFi system from that era nonetheless )

However i have a small problem now, and that is that i can't get the idle speed below 1000rpm, even with the idle screw fully turned it ( in theory the engine should stall or idle very low if you do that )

I cleaned the throttle body when i did a clean up of the engine bay, it has a small hole on the top of the throttle body housing which is where the air flows into the engine with the engine at idle.

Upon starting the engine immediately i noticed the idle was really high, about 1200rpm ( cold ), as it warmed up it went down to about 1100rpm.

This is what usually happens when i clean the throttle body as it tends to get gunked up due to the crankcase ventilation system pushing oil vapours into the inlet ( thinking of installing a catch can instead )

However i always have been able to then simply turn the idle screw until it idles nice and smooth at around 900-950rpm, now even with the screw fully turned in i can't get it lower than 1000rpm ( 2 full turns from where it was before )

A few weeks back i advanced the timing a little bit, from about 8 degrees to 12, it was idling at 900rpm before than and about 950 after adjusting the timing.

I tried setting the timing back to where it was before, but that made little difference, the only way i can get it to idle at 900rpm or so is by retarding the timing to around 4-5 degrees, and the engine just doesn't like that.

Now i suspect i either have a vacuum leak somewhere, or the auxiliary air valve has stuck open, creating a vaccum leak.

In case you don't know the Bosch K-Jetronic system uses a valve that uses a bi-metallic element that bypasses air from before the throttle body into the inlet manifold, when the engine is started cold it's open, which raises the idle speed to achieve a smoother cold idle.

Once the engine begins warming up it is supposed to gradually close until it's fully closed once the engine reaches full operating temp, so i suspect that it works but is not closing fully.

I also think that it's running rich both cold and warm, the last time it was checked it gave a CO reading of 2.25, when according to Ford it should be around 1.0 - 1.5, could this have something to do with it?

Other than that the engine runs great, even though it idles at 1000rpm it idles very smooth, just too high.

 

[Astro14]

Vacuum leak - or, in the case of my K-Jetronic cars, there was an Idle Air Control Valve. If so, the Idle Air Control valve isn't fully closing.

This sounds a lot like your bi-metallic valve. Though the IAC was electronically controlled on my cars, it served to add air for cold start and warm up (as well as when the AC compressor kicked on) to raise the idle.

I would suspect that your bi-metallic valve isn't closing, or had gunk in it that prevents closing.

So, whether the extra air is coming in through a vacuum leak, or through this valve, you're getting extra air...

 

[FCD]

That is my main suspect right now, that Idle air control valve is the same thing as a Auxiliary air valve, it's just called that in my haynes manual.
I will look for possible vacuum leaks and if i don't find anything i'll have to take the valve out, which is a real pain as it's a transversely mounted engine and it right at the back of the inlet manifold and behind the warmup regulator.
How do i test if it's working?

 

[tcp71]

My 88 Audi 4000 had that system. As stated, vacuum leak or the idle air control valve. The IAC runs on a pulse modulation signal from what I remember and it can get gunked up as well. People used to remove the valve and pop it with 12 volts from the battery to get it to move while spraying it with carb cleaner. It was the usual problem for high idle.

 

[barryh]

I had Bosch Ke on a 1989 Mercedes 190e I ran for 21 years and the cold start air valve it had could be adjusted. It was easier if the valve was removed (and yes it was a pain to take out) but once I'd seen how it worked it was possible to adjust it in situ. Removing the top air hose allows you to look down inside the valve where you can see if the aperture is closed or open when the engine is hot. There is is small lock nut that can be slackened off to make the adjustment on a trial and error basis.

 

[FCD]

Thanks for the replies, yes the valve does have a small nut that i can see is painted in yellow as to indicate that it has possibly been adjusted before?
However in my case i think it's a matter of probably it just being dirty and not closing fully, do you think spraying brakleen in it could help?
I'm pretty sure the valve does work, because when you first start the engine the idle goes way high, about 1200rpm, and gradually goes down to about 1000 when it's warmed up, so my theory is it works but doesn't fully close for some reason.
I will try to have a look inside the valve with the engine warm, however i will have to try and record something on my phone as it's right at the back of the inlet manifold and it is very hard to get to.

I actually think that back when i bought the car 2 years ago the valve didn't work at all ( stuck closed ) because it used to idle low when cold, and it's somehow began magically working again, so it's open when cold as it should but doesn't fully close.

Ahh, the myssteries of K-Jetronic, i have a love / hate relationship with it

 

[FCD]

I think i've found my problem actually, blanked off the auxiliary air valve and it only made it idle really badly when cold but just as high when warm.
As it turns out it's sucking air through the idle adjustment screw! it has a small o-ring which i assume has given up the ghost and that's why i can't get it to idle below 1000rpm.

 

[barryh]

Very fine thread that idle adjustment screw. Always amazes me how little air an engine uses at idle.