As usual my car is not behaving. I need to get it to pass emissions... but first I need it to idle properly. Its always had weird intermittent trouble with this, and I actually had a very old thread going but I don't think I ever got results... https://www.jaguarforums.com/forum/x...efresh-268297/

A lot has happened since that thread as well, so I'm not sure its very relevant. But I'm going to link the 2 together for posterity...

What the car does: When I turn the car on it idles around ~900 rpm. It behaves itself for maybe 5~10 minutes before it begins creeping up to 1400~1800. Turning the A/C on raises the idle, turning it off brings it back down *mostly.* Pressing the gas does a similar thing, the rpms go up and then come *mostly* back down. I believe the engine getting warm is also having an effect. The net result is that after 15 minutes or so, idle is over 1400.

What I've tried so far: I was suspicious of the IAC valve so I unplugged it, the car behaved exactly the same. (I remembered to plug it back in!) I tested for vacuum leaks by capping the intake with a rubber glove and blowing in through the brake booster, inflating the rubber glove and listening for leaks. I found one vacuum leak (loose clamp) and fixed it. That got the glove to hold air like a balloon. That intake is sealed tight. The idle still climbs. I unplugged the coolant temp sensor up top, that raised the idle a lot. Plugged it back in and it went back down. The throttle pedal isn't stuck down, I can put my foot underneath and pull up, with no effect on idle. The cable seems to have enough slack. I also wound the main throttle body spring an extra rotation.

Things I've done recently: As mentioned in my no-start thread recently, I went through the whole intake side to do the octopus hose. All the gaskets are refreshed, the throttle body itself got cleaned again. (I was in there, why not). The car has a brand new and fully charged battery. I tested the EGR hoses for leaks, they checked out good.

At this point I'm really starting to question the ECU. A problem I thought was unrelated, my key fob and the lock button in the car no longer work at all. The car is really rustling my jimmies here.

 

More notes: I just checked the line to the brake booster, that check valve is working. I also verified the cruise control wasn't sticking or anything.

 

i previously had high idle in my car a couple years back.
the only thing that sorted it after trying everything was a TPS calibration.

and yes, i know all too well of how things like this really just confuse the hell out of you and make you go bananas

so the throttle is not sticking at all?
as if it was i would say to add an external throttle return spring that is seen on some but not of our cars.
that is if you don't already have.

do you have a scanner to check stft?
maybe o2 sensors are kaput and car is over fueling?

 

My issue is the supercharger bypass. If I blip the throttle, the idle drops. Try locating the area and giving it a spray with a lubricant of some sort and move it with your hand if you can. The return spring for that is quite weak so maybe try replacing that. But anyway if either of those work, there's your culprit.

 

If you are fairly certain that the throttle body is relatively clean, and not sticky, it would most likely require a TPS Reset. A dealer, or a specialized shop with Jaguar specific software could do this for you for no more than 1 hour labor, even though it will take them minutes.

I don't know where you're located, but there might be a forum member than can help?

I realize it's a chore to get to the throttle body with the supercharged engines. I would recommend giving that throttle body a thorough cleaning before you get this TPS reset.

 

I've already cleaned the throttle body so many times at this point. I don't think there could be any dirt left. Last time I did a TPS reset at Schearer's in Allentown PA. A bit of a hike to get there, and the repair didn't last. It was better on the drive home, seemed to behave. Then the next day it was over 2000 rpm again. I think it could be worth another chance but I'm leery.

I tried disconnecting the battery, letting it sit, connecting the negative and positive to completely drain everything. Then I did an internet "throttle reset". Turned the key to "on," pressed the gas pedal all the way down and held it for a little bit. I let the car idle for a good 20+ minutes and it was hanging around 900 rpm. I want to test it more though, I don't trust it yet.

 

4 new O2 sensors, did the extra winding on the throttle spring + the extra entension spring. Pretty sure the throttle blade isn't sticking, the cable could be a little bit nicer but its not holding open.

 

The SC bypass is subject to some discussion on this site , as well as specific to the SC engine problematic idle , I don't have SC but that one appears to be more sensitive , this may have to do with a boost in intake volumes and the regulations after that to tame it

There was a component that has negated during later XJR production years I beleive had to do with breather gas guck build up

If setting up ELM - 327 live data look at PID / EGR _ ERROR target 0 % as this is your agrement that the EGR has arived to commanded postion , wouldn't expect perfect 0 but some lag , The IAC vavle does not have this feature on the X300

You will see this extra SC component on page X of the 801s doc I hope will link in a bit

Or may be in a TSB

 

It's at the end of the AJ16 engine just before the CEL codes list , can't see page as my computer " lacking " * $%#@&(^%

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

 

Disconnecting the battery for 2,000 years wouldn't reset anything. The fuel trim settings are set in RAM.

The throttle reset isn't a thing on these cars either. Neither is the disconnecting battery leads and bringing them together.

There is a test of the IACV that can, at the very least, ensure that it is working properly. You can probably do a search for that on these forums.

I'm sure you've checked to make sure the MAF is working as it should?

Coolant Sensor can also do this. I see you unplugged it and plugged it back in, but it's a $20 part, and should be easy to get to.

 

Vee ,

Your slight twist of the pins / blades of the MAF connector and maybe the same on the IAC valve connector ?

The MAF is feed 12 volts battery from a relay and a splice between the relay is the large # 5 right ECU controlled relay , swapping options as a headlight , fog , A / C clutch

The splice meens the power is shaired with a couple other engine regulation sensors that can be at fault " sucking down " the full power to the MAF

 

I don't have a great way to test the MAF. All my OBD2 readers have the glitch where the MAF reports miniscule airflow. I thought this was a problem when I first got the car, and bought a second MAF. It behaved exactly the same. And the car wont run at all with it unplugged.

I drove it a bit more last night, its still doing it. Its tolerable but still weird, and I'm worried this will stop the car finishing its OBD2 monitors for inspection

 

As long as the MAF is low at startup, and increases with throttle, its likely fine. Its really not a common failure. You have two, it's probably not it.

It should definitely not run without being plugged in.

Failing FOB usually points to a dying battery. It's true. The car will receive the signal but won't actuate all, or any of the locks. That means the battery is not long for this world.

 

BTW, closest I ever get to Allentown might be Shamokin, PA....or Princeton.

 

This is extremely simply to diagnose. You start the car, open live OBD data and check value under TPS, e.g should be showing 11.XX% or 0.65V(depending if your scanner is showing it in % or V). Drive it as usual and wait until idle creeps up, check OBD TPS value again - if it goes by more than 0.02V that is exactly why your idle goes up too. This the only thing that sets up idle, nothing else except for an air leak could do it.
If you confirm it goes up, there are only two three things that could cause it.
1. Cable issue, either too tight or you have a pedal issue
2. TB plate binding up, cleaning it properly actually requires sanding it down if you want to get rid of the gunked up oily deposits, then you have to set up TB plate gap correctly too while also looking at the TPS.
3. Dying TPS, maybe it just changes voltage when it all heats up.

PS

Some cars happily run without plugged MAF, half of mine did, the other half didn't. Must be down to ECU version but I never figured it out.

 

I fiddled with it a bit more. TPS was around 13.5%when I first checked it. I adjusted the grub screw and got it down to 11.9%, but the throttle plate was sticking so bad it was unuseable. The TPS also has issues reporting less than 11.9%. It was spotty at best, it feels like the potentiometer has a dead spot, or perhaps the TPS got clocked by accident and literally cannot rotate anymore. (?)

Then things got weird. I adjusted the grub screw back to 12.5%, the throttle plate still sticks but not horribly. I let the car idle for awhile with no creep. I had some other stuff to do so I let it sit idling, with the throttle blade at 12.5%. After about 20 minutes I checked back in and saw the TPS at 0.4%. Point 4. Car was still idling just fine, no creep at all. It also gave me 2 pending codes: B30F4 & P13B0.

At this point I'm still going to poke around the car and see if I can fix things, but I'm really not keen on digging back in to it again. Tentatively going to sell it, but its a hard sell.