I have been working through the infamous high idle issue on my 1997 XJR (US) with 59K miles. Yesterday I dismantled the air intake and removed the tubing that goes from the supercharger to the intercooler. There was a strong smell of varnished gas and the build up of varnish in the tubing and in the intercooler was significant. The butterfly in the throttle body is sticky and I will need to remove it to properly address the high idle. If I manually push the cam that the throttle cable pulls down to the close position, I get a proper idle. As soon as I push the accelerator, it goes back to a high idle (1200-1400 RPMs) until I manually push it closed.

This is my first supercharged car. Has anyone with an XJR found the need to clean the intercooler?
Thanks.

 

There is a TSB on a stronger throttle return spring to bring it back to idle mechanical stop

TBS coming

Do not remove or adjust the TPS sensor yet until learning some things but your manually placing the butterfly to idle mechanical stop does say something

 

See page 13 for supercharged and the previous page 11 for normally aspirated

05.1-26 amend4 (R493) (jagrepair.com)

Some solutions not having the uprated spring is use the original spring but wind it more ( preload ) before installing it in a new position , or a 2nd external spring at the throttle cable bellcrank located before going into the throttle body butterfly shaft bellcrank

 

The deposits on the intercooler may be from the original factory Air / Oil separator located inside the valve cover

This oil that gets by binds up the throttle body upstream / before the intercooler , also the inlet air temp sensor ( efffects idle )

There is a factory TSB with an external catch can solution and some aftermarket catch can solutions

On later model supercharged there is a component ( PART LOAD BREATHER ADAPTOR ASSEMBLY ) that leaks in the intake stream that was deleted and not installed

I do not have the supercharged model

See page 108

801S TITLE (jagrepair.com)

 

http://www.jagrepair.com/images/TSB/...igh%20Idle.pdf

 

Thank you for all this information. My car had the EGR 493 Enhancement in 2002. That said, the return spring looks weak to me. I will investigate getting a stronger spring.

The catch can sounds like a great idea. A friend of mine swears by these on all his vehicles. I have seen what they collect and it is easy to see how it may cause issues over time of feeding that oil mist back into the intake.

Given how dirty the supercharger plumbing and intercooler are, I am assuming the throttle body is equally bad. When I get some time, I will pull that and see about removing it and cleaning it.

Thanks again for all the information.

 

You may be seeing a 2nd added external spring to assist the original around the butterfly shaft spring

Your supercharged TB as definitely different with an original external spring than mine , normally asperated

There is a precaution to not getting solvent into the inlet air control valve to damaging the IAC motor , there is a teflon seal to prevent this on all car manufactures and unknown if the upgraded teflon is on this model

Do not remove the IAC valve as snaps off the bolts , loctited so heat needed , 5 . 5 mm on mine , but do ensure there is a gasket between the IAC valve and the TB , missing sometimes

 

gasket missing off mine.
but there is an o-ring around the iacv. (seen in pic 2)
I have seen them sometimes sold with gasket,
sometimes sold with o-ring

there is a seat on the TB for an o-ring to sit
I don't see that there would be a need for both. aslong as either one is present you should get a good seal.
correct me if i am wrong

pic 1 with o-ring
pic 2 with gasket

 

There is the sealing to prevent more air intake then the valve poppet position

But more like a poppet extension position and how the poppet to poppet seat gap difference effecting air flow

Which raises the question

When the ECU notices the TPS is at the idle stop, is there only 1 IAC ( close to closed ) position and the idle RPM should fall in line

or does the ECU have a target idle RPM and regulates the IAC and fuel trim to achieve that

Being the idle RPMs can be out of target , the later should not be the case

If the TPS does not arrive at the idle stop or out of adjustment it doesn't hit a trigger sensor value if a trigger is the case....

So this comes back around to the accuracy of the IAC valve poppet seat gap and how a gasket ensures this vs. a O - ring

 

interesting theory.
but.
think back to when i had my high idle issue previously.
it had a gasket originally. idle was very high, whilst working on it one thing i did was remove the gasket thinking it may lower it.
it did nothing.
tps reset however got it running and idling perfect.

i have just now swapped my ecu and my idle is now sitting just slightly high (about 680) again.
off today to get a tps reset.

so from what i can see from this is that the gasket does not matter as long as it is sealing.
the ecu will sit it where it needs to be.

the only reason i can see for a gasket as opposed to just an o-ring is that it will space it out incase of total failure to stop it closing fully up.
however i feel that at normal idle the iacv would not normally be fully extended and a gasket would not stop this.

i suppose one could (atleast partially) test this by placing 2 or 3 gaskets in and seeing if the car is able to maintain correct idle or is forced into high idle situations.


i do intend to put a gasket back tho, i just totally forgot about it being missing. when i was originally working on mine a year and half ago the gasket got ripped and i forgot i did not have it there until recently i was rechecking everything due to stalling and non start which i discovered was fuel pressure regulator and ecu.

 

here is something interesting parker.
slightly confusing.

according to the jag classic parts the gasket is only in situ on the 3.2L

 

I had quite a lot of dirty oil in my whole intake when I refurbished it. I cleaned all the tubes and elbows pretty thoroughly. The intercooler had collected a ton and eventually I gave up washing it all out. About 113k miles on the car.