1995 X300. 112,000 miles. 6 Cylinder, naturally aspirated.
At post-purchase inspection, shop replaced all 6 spark plugs and coils. Without asking, they also cleaned the throttle body to remove carbon. Car idle, which was previously spot on, is now 1,000 - 1,100 rpm. Looking into the situation, my best guess is that cleaning the throttle body fouled the throttle position sensor/throttle potentiometer (mounted on the underside of the throttle body) with goo, making the throttle position sensor malfunction. Question: If I remove the throttle position sensor and clean it out with Mass Airflow Sensor cleaner (safe for electronics), is that likely to restore proper idle? Are those throttle potentiometers repairable, or do I need to spend $475 on a new one?

I have adjusted the throttle idle set screw (hex screw mounted on front side of throttle body), which yielded a minor improvement, reducing the idle from 1,300 rpm down to current level of 1,000 to 1,100 rpm.

 

The middle wire on the TPS sensor color Greeen / Yellow with the key on and not running should read 0.60 + or - 0.02 volts DC . You can follow this wire as it goes over the fuel rail and tap into it there .

The throttle cable can bind up including the cable end fray on the butterfly tower shaft bellcrank and there is a TSB on replacing the return spring with a stronger part number and can be done yourself in a mod without a shop visit or Jaguar replacement part .

The TPS is sealed just enough for the guck to flow it from above , but cleaning the sweeper arm brushes is hard to do through the same manufacturing gaps .

See page 79

http://www.jagrepair.com/images/Trai...20-%202000.pdf

And page 50 - 51 below :

http://www.jagrepair.com/images/Auto.../jagxj1995.pdf

Verify the throttle cable is attached to the correct hole on the last clamp before the tower marked A and M for the transmission installed as it may have been disturbed .

 

 

The TPS can be adjusted from the top side without jacking the car or removing the TB but takes alot of patience and a few beers before hand for the heat of battle

 

The AJ16 TPS are not slotted like the AJ6 TPS.
You can enlarge or slot the holes to gain a little room to adjust but I just use one of my WDS or IDS units to calibrate the TPS.

Performing TPS calibration is the correct way to set idle.

You might also want to check the function of the IACV (same as a GM IACV on TBI engines).

bob

 

If the IAC valve was disturbed the the seal between it and the TB that has a gasket that gives problems or left out ..

There is no seal between the TB and the intake manifold .

Cleaning fluids may have entered the stepper motor of the IAC valve and the poppet may be in a too open position as it scheduled closer to close on engine spool down .

The IAC valve body to TB screws are a odd size like 5.5 mm or 6.5 mm and get stuck and snap off for they are loctited in so choose your battles

 

To remove the IACV mount bolts, I ALWAYS use a small butane torch to heat the throttle housing where the bolt threads are located.
This helps to melt the threadlocking compound and the bolts are less likely to snap during removal.

The hex head is 5.5mm.

bob

 

I also had a high idle after I cleaned my throttle body. Tried adjusting the idle with the manual screw on the side of the TB. Finally found out what was causing the high idle. I forgotten to plug in the electrical cable at the bottom of the throttle body. I plugged it in and it worked great after that.

 

Good point , As I received mine ftom the PO the metal locking clip for that connector was doinked off with a screwdriver so the connector was just setting on there and not locked .