I have a 87 xj40 sovereign. Idle is rough and stalls straight after start up. A friend who has done a lot of work on electronic fuel systems has established that air is leaking through the coolant sensor when up to operating temperature ie vacuum at the hose when disconnect before the butterfly valve. Mine has the sensor bolted to the intake manifold with 2 hoses that carry the coolant and a third one for air. After removing it from the manifold and looking into the cavity there is a hole for the air intake. On the coolant side there seems to be an oblong gap. Is there something that is pushed out of the gap that closes off the air intake when operating temperature is reached. On the outside on top above the coolant hose fittings there is something that looks similar to a frost plug. Ant help in understanding the operation and the cause for the unwanted air going into the manifold would be appreciated
Post a pic and describe your bits by referring to the pic(s). I think your friend is possibly mistaking some of the components for things they are not? Also I’m sorry but I find your description of the parts hard to follow …
This is on the intake manifold between injectors 3 and 4 and marked 1 in the photo. When I had it off I blew compressed air through the coolant ports. After installing it I found that it did heat up as the motor warmed and the idle revs dropped although it does idle lumpy. I manufactured a new fitting to fit on the intake between the MAF and the butterfly valve as the original seemed to be a compressed air hose fitting and was letting in air. Obviously the original factory part had a fitting molded on to the air intake . This supplies air to this apparatus via a hose which you see in the front of the photo. The back hoses which you only see one of is for coolant. Would it be an air heater using the coolant temperature as a heat source. Just thinking about when the idle revs drop. In defense of my friend , when he lived in Britain, he serviced Audis and Porches as well as race bikes so he does know a bit about EFIs. His comment was Jaguars should be super smooth at idle
Sorry I’m just as lost as before, no idea what that thing is - not sure my car (94MY) has that. The Idle control valve is located somewhere around there but for me, your close-up is too close to see what the arrangement is.
The coolant temp sensor is at the front of the motor just back of the thermostat housing, not there.
What is this butterfly valve? Are you talking about the throttle butterfly?
Maybe if you backed up with the camera and took a pic I’d have a better overview of what your engine compartment looks like.
BTW, do you have a Haynes manual for your car?
In looking at my 4.0 1990 car that device with the two small coolant hoses and one hose near the number “1” is for the heated crankcase breather system. You will see the lower hose in your photo leads to the breather hose. Jaguar had a coolant heated breather system probably to keep it operating properly.
Mine is a 3.6l and my filler cap is on top of the breather hose dropping the oil straight into the sump ,as opposed to some I have seen on the cam covers. The breather hoses are in this area but not connected to the “no.1”
Cant find it in the Haynes manual although it does start at 1988. Mine is a 87. Any further back with. the camera it will be lost. The stepper motor is on the next gap between the injections further forward. This sitting on the intake manifold directly after the butterfly valve. In fact if you look you can see the throttle control in the photo
Rod,
I don’t know if these extracts from JHM1130 CD-Rom for the '87 model helps.
“Crankase Ventilation
Piston blow-by gasses are scavenged from the crankcase and the camshaft housing via the oil filler tube. These are collected and fed in to the engine intake manifold at part throttle through the part throttle control orifice (item 1 in your picture) and at full throttle through the air intake elbow”
“Ice Prevention
To prevent possible icing-up during cold weather, the control orifice and the hose to the air intake are heated. The control orifice is continuosly heated by the engine coolant; the (electrical) heater element is energised via a relay signal from the windscreen washer jet temperature sensor”
There is a nice picture in the JHM1130 illustrating this but I don’t know how to link that to this post.
I have just looked at my 89. 3.6 and you are talking about the idel control valve
I stand corrected. Had another look at different pictures in the Haynes manual, not the one where all the components are identified, 4.8 diagram11.1. In 4.8 pictures10.3 and 10.9 ,the attachment I am trying to establish it’s use is directly behind the throttle linkage. You can see the heads of the 2 studs.
Hi John
Not sure. If you have a Haynes manual it is in chapter 4.8 diagram 10.3 and 10.9. Refer to my previous reply
You do not show your location but in North America the first of the XJ40 cars were sold as 1988 models at the launch in May of 1987. So had sale dates in 1987 but were nominally 1988 models. True 1987 cars in NA would be the last of the Series III XJs. This may not be true for other market cars thus important to show your location in your header info for forum members to provide accurate responses to issues. .
I think in later years (at least on a 94) they moved the function of this component to the underside of the throttle body.
If you think this thing is causing your vacuum leak, why not temporarily plug it up or pinch off a hose or whatever and see if the car runs ok? The component itself is not an actual sensor so disabling it shouldn’t affect the engine starting.
Major vacuum leaks are often caused by pinching the large corrugated intake hose at the throttle body with the large hose clamp.
After futher research in Haynes this after noon I found a diagram of thr air intake before the throttle linkage. It shows a air temperature sensor where mine has the hose fitting coming from “no1”. Clamping the hose at idle results in the motor stalling at idle. So more head scratching and reading. The rev drop when reaching operating temperature would have been due to the temperature sensor on thermostat block. Someone who previously replied to me suggested it was part of the breather system so this could be correct. May take the air intake sustem off again and see if there are any clues that I missed last time