I've been fiddling around with my 87 all day trying to get the idle down. It was idling at 1500 rpm in park, after setting the butterfly gap its more like 1800 rpm.

-cleaned idle control valve/adjuster
-checked that AAV is closed
- sprayed half a can of starting fluid anywhere and everywhere
- checked any vacuum hose I can find with a gauge to see if it would hold vacuum

So far, nothing has brought the idle up or down, except pulling the cap off the bung at the idle adjuster. Haven't turn up any leaks checking vacuum lines. I've also changed the idle at the adjuster and it doesn't seem to do anything.

Any ideas where to go from here? I'm pretty close to taping off every single inlet at the manifold to see if it goes down. Is there some vacuum line I could be missing?

EDIT: I just pulled the AAV hose, it wanted to die ASAP, but returned to high idle when I totally plugged it. Maybe its running lean? It does take quite a bit of cranking to get going and it returns from revving slowly. Are the only possibilities the mixture from the MAS and clogged injectors?

 

check all the hose and clamp connections starting at the front "trumpet" of the air filter, all the way to the 90 degree aluminum elbow at the intake. A leaking hose in any of those connections can cause a high idle.

 

distributor timing ? Gas pedal not operating smoothly ? Cable hanging up ? weak return spring ? intake manifold tight ? Cap on drain under intake manifold (not visible but it should be there covering the intake manifold drain).
Set timing to spec and change out the vacuum hoses for new ones. guessing...

 

Before doing anything else, check that throttle cable as Allyn suggested. They are a bit notorious for binding.

Disconnect it at both ends and operate it by hand. Should feel "like buttah".

The cable has a nylon (or similar) inner lining which can wear or degrade......often worsened (or caused) by poor engine grounding. If the regular engine ground is poor the throttle cable *becomes* the de facto ground path. This overheats and damages the inner lining.

I also agree with checking the ignition timing

If no joy we'll start looking at other possibilities.

Cheers
DD

 

The throttle cable is actually a little loose, probably stretched. I don't even see where it is adjusted. It looks to slot into the pedal linkage and the TB, but the sheath is adjustable at the TB? Anyway, the throttle is resting on the stop.

I'm new to the XJ6, but have noted a good bit of the lines on the intake manifold so far. I believe I've checked every hose, but don't know anything about a DRAIN. Is it visible in any diagrams or can anyone describe where to go looking for it?

Are the timing marks up top or down below? Front of the engine is kinda grimy so I haven't noticed any. There is a bit on the left side timing cover thats definitely over the crank pulley, looks suspiciously liking a timing mark to me. Is the crank pull indexed with something that can fall off or wear away?

 

Presumably top left in this pic? I'll have to check that out.

 

So, no change after plugging the drain hole, though the old plug was kinda soft and gunky.

I pulled the hose connection to the AAV from the idle control valve and blocked off BOTH sides. This pulled the idle down to around 1000 RPM. After fiddling with the idle control, maybe I am just off a bit or it hasn't warmed up.

Should the engine be getting air there at startup and I am masking the problem or does that mean the AAV isn't working correctly?

How closed will the AAV get? Should I not have any flow through the AAV at idle? If I run the engine and uncover the AAV, I can see the hole is nearly obstructed except a small hole.

Or is it possible this is indicative that the idle control valve itself is letting to much air past?

Other checks:
- timing light on left side of engine where I think there is indicator provided no info, didn't see any pulley marks
- swapped CTS with brand new bosch coolant temp sensor with zero change
- adjusted AFM gear position and idle bypass to little or no effect
- Quick check on the O2 was showing 0.11v, so def lean

EDIT: At 1100 RPM the timing at 10 deg BTDC. Spec is something like 17deg at 800 RPM. Will fix timing tomorrow. I had to slowly bump the engine around and look really hard for the timing marks. Eventually found them and did the ole white paint on then wipe off trick.

 

Yeah, there's always some oily gunk in the inlet manifold that turns the rubber cap into a gooey thing


Well, that's a lot better than 1500-1800 !

After plugging off the AAV did the engine respond to adjustments at the adjustment screw? It should. If not, the passageway is clogged or you have another source of incoming air.

Did you remove the air distribution block for cleaning? And, if so, did you reinstall the overrun spring the same way it came out? (Not sure if it matters....but it might. I'll have to mull that a bit)


The AAV should be open when the engine is cold....just like the V12 AAV....to increase idle speed when cold


Or is it possible this is indicative that the idle control valve itself is letting to much air past?

As i recall a small opening when warm is OK/normal. Not sure why it wasn't designed to fully close





My 6-cylinder memory is foggy on the matter. I'll do some checking on the timing marks

It shouldn't have any bearing on idle speed anyway


Idle bypass? On the Air Flow Meter?

Un-metered air entering....which would typically lower the idle speed. Hmmmm.

OK good. But advancing the timing back to 17º will likely just increase your idle speed

Cheers
DD

 

You turned the idle screw adjuster all the way closed and its not effecting the idle at all? the allen screw adjuster on the intake/air distribution block? The engine should be ready to die with that closed.
Sounds like the AAV is working correctly.
Are you sure the ECU is getting the sensor signals back from the CTS or AFM? the connector plugs or wiring isnt damaged?
Sometimes the seals around the injectors leak also

 

It did affect the idle by not by much. Lot of adjusting to only change by 100 RPM or so. The air bypass screw (accidentally said idle bypass) made a small change in smoothness within 1/2 turn or so but any additional turns didn't seem to do anything. I moved the gear on the AFM by 90 deg and didnt seem to notice any difference.

I am not sure about the signal at the ECU, not even sure where it is located in the XJ6 lol. A poor connection at the CTS would result in high resistance, so more fuel. Not sure about the AFM connections, I'm pretty sure voltage goes down as the door opens. If it was off by the same amount, a set resistance, wouldn't it run worse at higher RPM? (It revs perfectly fine).

 

If the CTS is getting open circuit it will be constantly on full choke.
With a multimeter check you get these voltages at the afm plug with ign on.
Pin 6 0v
Pin 7 2.25v - flap fully closed
Pin 7 7.5v - flap fully open
Pin 8 7.6v
Pin 9 12v - nominally 2v below battery

 

Two items often overlooked are the seal on the engine oil dipstick and the oil filler cap gasket. Both can cause unmetered air to enter the system.

 

You may have already found this and had a read, but good information about the 4.2 litre XK EFI:

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

 

Did you remove the air distribution block for cleaning and de-gunking?



Mounted in the trunk on the forward bulkhead


Which would not increase idle speed.


Cheers
DD

 

I didn't attempt to adjust the idle again after this. I did initially have the idle adjusted quite a bit down from where it was, so if blocking off the AAV returned the engine to "normal" conditions, the idle should have dropped to less than normal, assuming the previous idle speed adjustment was to 750 RPM.

Yes, I cleaned it. Its sort of just a spring with a valve, not much to get dirty. The lines are clear. There is only one way to insert the spring


I noticed other years use 8 deg. Maybe someone set this one using the spec from another year. At 1100~ RPM 10 deg is probably close to 8 deg at 800



Meant to say air bypass

 

Yeah, point being a bad CTS connection wouldn't cause a lean condition

 

I agree.

Weird problem !




Or someone else was trying to bring the idle speed down?


You got this car fairly recently as I recall, yes? Is this high idle situation a recent/new problem? Or has it been there since you bought it?

Makes sense, yes

Cheers
DD

 

Readings were as follows:

pin 6-0.03v
pin 7-2.23v CLOSED
pin 7-6.78v OPEN
pin 8-6.94v
pin 9-10.78v

 

Yes, I recently acquired it and I just got the car running after having sat for 10+ years. It wasn't running because the cap and rotor were in horrible shape and the CTS connector was rusted away. So there is no "normal" idle, 1600 RPM is ground zero for me.

 

Interesting....seems like I need to switch gears for diagnosing the problem. I believe I got a false reading off the O2 before. Yesterday it read 0.85v, so it is actually running rich. I didn't see it change from low to high, so I should check again.

I've also noticed at startup the car doesn't immediately go to 1500 rpm, but takes 10-30 seconds to get there. I wonder if that is the AAV or maybe the ECU responding to some sensor.

I need to find a diagram of the ECU to check what its getting from the CTS to make sure that is right (PIN 30?).

A little confused, as I would have thought running rich would have only made the idle rough without extra air. Although it does seem slightly rougher after adjusting the timing more advanced.

I think I'm going to see if I can hook my compression tester into the cold start injector to check fuel pressure. After a few seconds the noise on the regulator cuts down, before I assumed the pump was clogged or weak (thought it was lean) so I entertained checking it. Now I'm thinking maybe the regulator just isn't opening and I have too much pressure.