Drops down to idle very slowly

X300
1

This topic was covered under XJ40 but no definitive answer was given.
What causes the car to drop slowly back to idle. It will eventually get back to idle, but in the meantime it requires a lot of braking. It will sometime drop back to idle if I blip the throttle.
The car is a '97 XJ6 with the 4.0 Litre straight 6 with 140,000 km. Just purchased about 8 weeks ago and I have done a bunch of things:

  • rebuilt front calipers (seized with rust)
  • flushed the transmission
  • new filter and oil
  • flushed power steering fluid
  • new air filter
  • new plugs
  • U-joints on both rear half shafts
  • shock absorbers
  • battery
  • upper and lower ball joints
  • 4 wheel alignment
  • adjusted front wheel bearings
  • exhaust system is rotten so next week it is replaced

Still to be done:

  • fix radio
  • fix that other display
  • drive it and enjoy it while I work on cosmetics

cheers

2

Start by cleaning the throttle body. It gets gunked up because of the camcover breather hose that connects back to your intake elbow. This is a very common issue.

The throttle body is held in place with four 10mm bolts. There is also a coolant hose going in and out from the underside. You won’t see it if you weren’t looking for it. A pair of golf tees is ideal to block the lines while the throttle body is out.

Removal is the best way to clean up the throttle body. You’ll need a can of carb cleaner spray and some rags. Shouldn’t take you longer than 10 minutes to clean down. Do not loosen or remove the throttle potentiometer sensor.

When you reinstall the throttle body there is NO gasket between the throttle body and the intake manifold on the engine. It looks like there should be one, but it is a dry fit. You could apply some permatex permashield if you want some kind of sealer, but it isn’t necessary.

Word of warning. You may need a TPS reset once you clean out this throttle body. There is a manual way of doing it, but you’d have to remove and modify the TPS to do it.

3

An ENHANCED throttle spring was introduced in the early 2000s.(NBB 3131AB)

In a pinch, you can use the old spring by cutting off about an inch of the long ‘tail’ and winding it one extra turn.

I used to use both methods when I worked at the dealer.

You can also add the XJ40 plastic arm and spring combination (AJ6) to the AJ16 engine.

It was all part of the RECALL that the car should have been under.

05-1-26am5 1995 MYRecall R493.pdf (256.2 KB)

4

I chose the easy way out. There are 3 springs on the assembly on top of the throttle body. The middle one seemed slack at idle, and the easiest to tighten, so I wound it one turn tighter.

Took the car out for a ride and the problem was solved! It may be temporary and if I get ambitious I will clean out the throttle body, but the idea of the tps needing resetting scares me. I hate electronics in cars.

Thanks for the help. Cheers

5

Don’t clean the throttle body until you need to.

6

I have lots of other projects so probably won’t.

BTW can you comment on an alternative transmission (6 spd) for the X300? 2k rpm at 80 kph(mph) seems like a lot of rpm for this car.

Cheers
George

7

If you’re asking me about swapping out the transmission, I cannot. I am no expert in transmissions.

I would recommend starting a new thread, or searching others? I know there is a way to put in a manual, but it isn’t cheap.