Troubleshoot: XJS 4.0 low idle

Turns out the part mates up without modification.
The car initially warmed up in normal operation. After going through the manual calibration the idle runs at 1600 RPM which is much too high.
I connected the WDS to run the maintenance routine and calibrate it that way but the battery is dead. Buying cells is $45 or having it rebuilt is $30. I suggested they just sell me the cells and say they rebuilt it. That is appearantly not an option, the privilege of rebuilding it myself is going to cost me so I'm waiting. I suspect once calibrated it'll be fine.

Here's the lucas labelled version...
http://www.partstrain.com/store/details/Jaguar/XJS/Lucas/Idle_Control_Valve/1995/2+2/6_Cyl_4-dot-0L/W0133-1607440.html

And here's the non Lucas version with special Jaguar pricing...
http://www.partstrain.com/store/details/Jaguar/XJS/Replacement/Idle_Control_Valve/1995/2+2/6_Cyl_4-dot-0L/REPJ313203.html

Are they funcationally equivalent to the one I purchased for $7? We'll see. I think the odds are in my favor.

Regarding cheap parts: I'm often wary of cheap but what I've come to understand about Jaguar is that their suppliers often deliver the same parts to different manufacturers. For instance, this same model of valve is used extensively in Peugeot engines and there's a great many other applications as well. The Jaguar version of this part is $150 - $450 (yeah, four hundred) and the others are quite a bit lower.

The one I selected appears to be a match for the one off my cat with a slightly different electrical connector. Best guess is it's the same part. This one comes with no associated applications.

But I'll let you know what happens. It's a risk since the part is physically similar but maybe not dimensionally or electrically identical.

Case in point, my aux fan went out. New motors of that config from the ontario company that makes them (for Jaguar and everyone else) were about $40. Jaguar wanted $350. I took mine over to an electric motor shop, we matched up a motor and voila. $40 and elbow grease later it's replaced new.

When the parts are inexpensive I don't worry about it. But when I'm noticing the gouging going on I go looking and usually it's pretty clear that I can get the same part from the same guys who make the part for Jaguar under a different label for steep discounts.

Jim, there really isn't a test procedure, per se, for that stepper motor. There are no gears in there or feedback mechanism. It's called a stepper motor because once initialized, the ECM counts armature segments [steps] to and from the initial position, to keep track of where it is. That initialization is accomplished by the same 'Throttle Pot Adaption' application I mentioned in WDS. By running that, the ECM then "knows" where closed throttle AND the idle stepper pintle are. From there it can correctly control the idle speed and 'tip in" fueling.

Good luck! I'm always wary of such cheap parts, but maybe it will work OK.

Cheers,

Weird but true. I think I found the part for $7.

http://www.partstrain.com/store/?N=0&src=search&Ntt=REPC313215

At that price I just ordered one and if it doesn't work out I can shrug it off. I'll let you know if that works out.

Jim right you are-normally one needs to move the throttle body out a bit--try SNG I think their stepper is about $100

Ah. Got it. Why does Jaguar hate their technicians? I was just barely able to get a 5.5 box wrench on that to remove the inboard bolt. Herm. There's no obvious way to get it apart or test it. The valve seat was a little grimy but not terrible. Looks like PCV gunk abd relatively minor.

motorcars is quoting $350 for this nothing part. I'll look around. Before I replace it I would prefer to verify the diagnosis with a test procedure. Anyone have a test procedure for this stepper motor or a disassembly procedure? It's a stepper so there's a toothed gear in there and probably a pot of some sort to feed back the step position to the ECU.

Jim that is the EGR --stepper is smaller--black--and on the top and slightly right on the Throttle body.

The term idle stepper motor is unfamiliar to me.

Is this what you mean:

http://www.motorcarsltd.com/lhe1550ab.html

Idle stepper motor - is this the motor on the EGR? I did verify that it seems to be functioning (actuates) though I'm not sure how to tell if it's actuating correctly or fully.

I'll try the WDS configuration for a new throttle pot and see where that gets me.

Steve you dog--you know it is the Idle stepper!

Idle stepper motor - is this the motor on the EGR? I did verify that it seems to be functioning (actuates) though I'm not sure how to tell if it's actuating correctly or fully.

I'll try the WDS configuration for a new throttle pot and see where that gets me.

Edited on 2013-12-26 17:17:28
Using the WDS you mentioned, select "Setup & Configuration" on the LH side. Then select "Throttle Pot Adaption" and when it asks, tell it you installed a new Throttle Position Sensor.

See if that gets you anywhere and report back. Your description makes me think you may have a failed Idle Stepper Motor.

Good luck!

One other datapoint. It's the 95.5 (96) model year so it does not have a distributor and has the GEMS ecu controlling coil packs on each cylinder.