X300 1996 3.2 aj16 bog standard. swb. RHD. Automatic.
on about 96k miles. New block and head on about 60k.

Right, out of the blue, you can start the car and it idles now at about 1000rpm (so a bit higher than before I changed the engine block/head, and yes the car was perfect running prior to the engine swap) and so I find if you touch the throttle while the engine is running, it sticks and it will NOT drop unless you get out and pull the throttle top back to get it down and make it idle again. The cables are free, the throttle body is clean, butterfly moves and closes fine, I have taken it off and cleaned it anyway, followed the suggestions of many threads saying of their sticking throttle/ stuck revs, and it all moves fine when the engine isn't running. Start it up again and it will not drop off as normal when you take your foot off the throttle. So it's suicidal to drive as it keeps bloody going lol. I can only now assume to change the TPS (the T-shape thing) underneath the butterfly valve itself? I have had no need to touch or change anything else on the car except the block and head I picked up as the easy task of changing the head gasket (the common oilway leak frontright) turned into a nightmare when the headbolt snapped in the block! At the time, quicker to get another engine due to lockdown and everyone useful was no longer working lol.

​​​​​​I try not to touch throttle bodies much as I know at least on the mercs they are peices of sensitive sensor crap and become expensive lol. But the TPS is what I'm thinking, these cars don't look particularly complex to be much else? I'm also thinking I'll have to take the car to the dealership to change it and set it up as ive never touched that sort of thing before and certainly have no one to hand to help who has done similar before; What's this re-setting about?

 

Jaguar issued a TSB a few decades ago to replace the throttle return spring with a stronger one.

When the new spring is NOT available, you can remove the spring, unwind the straight end about a half turn and cut off a short section.
Reinstall the spring with an additional turn. TADA.

The throttle spring info is toward the end of the TSB. The TSB was issued for the North American market so all of it may not apply.

 

Welcome to the forums Maxen D,

I've moved your question from General Tech Help to X300 forum. This is the place to post technical questions about your model.

Graham

 

Well I thought a return spring, but the car didn't have that when I bought it and it was spot on, it has two cables leading to the throttle body and the first one was threaded through the M for manual. Which it's automatic. Made no difference. I will measure up and bung a big Spring on it to see if it does cure it. But funny how the car was fine without it and now it's sticking.

Certainly no faults on the OBD reader either which is good btw. Only know this as the car certainly is not as nice and smooth running as before, hunts/ a little bit rough.

 

Other then the throttle return spring bringing the butterfly closed on the idle stop the Inlet Air Control valve must come to a partial open position and not be fully open or fully closed .

The 4 wire IAC valve can be sticking or the stepper motor that drives the valve can be bad

Removing the valve body can be difficult as the bolt head can be too close to other things nearby and the thread lock can even cause you to shear the bolts off .

They are a odd size like 5.5 or 6.5 mm

See page 88

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

Best to remove the throttle body and apply heat from the inside to loosen the thread lock or possibly breaking the bolts

Someone recently found the EGR valve coked over from oil vapors and once cleaned got his idle under control

The EGR has a position sensor built in and can be seen as EGR_Error as a PID with the ELM 327 and the target value is 0

The IAC valve does not have this commanded position followup

 

I MAY have solved it, in probably a bodged way, but I took off the cap with your two arms in that connect to your cables.... The spring under that I simply wound 1 more time and put it back together and it works as it it should! YES I have a spare few springs just incase it does not last lol. I can finally go for the MOT again safely, will let anyone know if it goes wrong after doing that! - and I was stumped before trying this as if I put a return spring in, one end I can attach but the bracket that hold the two cables' adjusters does not have any room to hook a spring round anyway.