That's great.

Lesson learned. Although the base setting for the TPS SHOULD be at 0.6v, if it has been adjusted, replaced, etc, and someone uses the PDU/WDS/etc to reset the TPS Setting with the applicable software, the base voltage is forever changed...at least until it is reset once again.

In this case, your idle might still be too high. 800 is still too high. In gear it should be in the mid to upper 500s, in Park it should be in the low 700s.

 

The idle was back up this afternoon ☹️️ I found the Jim butterworth page that describes resetting the Iscv. by taking the valve out of the TB and switching the car on to have it unwind. Has anyone done this?

 

No. Take it to a shop with Jag specific software and have them reset your idle. It's $150

been there done everything else. Cut to the chase.

https://www.jaguarforums.com/forum/xjs-x27-32/need-help-fast-idle-96-4-0l-150942/page2/

see post 26 if you want to make a last ditch effort

 

Update: I took it in to a semi-local European mechanic that told me the had the proper program to reset the idle. So, $158 fix didn't do anything. They told me they did the reset but that the idle is still high because I made a vacuum leak. How can I have a vacuum leak whe I do the manual reset and it idles fine...I turn the car off and it's back to 11-1200 rpm 😡

 

EDITING

IACV ( bipolar stepper motor ) resistance readings at ECU ( electrical integrity check only ) at ECU connector :

Coil 1/2 ==== Black 3 to Black 29 ===== 52.8 ohms

Coil 3/4 ==== Black 28 to Black 16 ===== 53.7 ohms

Test for step actuation with valve off TB :

Wire----- 3----- 29----- 28----- 16 Still working this part for correct pinout


Step 1----- 12v----- 12v ----- G----- G

Step 2----- G----- 12v ----- 12v ----- G

Step 3----- G ----- G----- 12v----- 12v

Step 4----- 12v----- G----- G----- 12v

A 9 volt battery might work for power source if not bound up


Important , check each contact for unwanted ground , may require tapping on IACV while reading for ground .

The X300 TPS is 3 wire and can be read with a meter with the engine off at the ECU connector as you move the TPS through it's range .

Wire GY is Red 12

GB is Black 7

UW is Red 11

X300 N/A and S/C is the same.

Look for a bip or spike to high on a needle meter as resistance as you sloooowly sweep it through , my not be able to see with a digital meter .

####### RESULTS #######

After rechecking at TPS sensor at setting 0.601 volts at idle stop

Paper clip into Red 11 to Red 12

Idle Throttle = 2235 ohms

Full Throttle = 230 ohms

 

Certainly seems odd. I had a similar issue and the reset fixed me back up. I threw a ton of parts at that thing before that.

Take some plastic wrap, wrap it over the air filter housing facing the engine, reinstall the air filter housing (with the plastic wrap), then take the hose off the at the intake elbow and start blowing some smoke in there and see where it leeches out.

 

There is a vacuum seal on the line that comes out of the intake manifold to the brake booster on mine that is loose but haven't resolved yet , You can push it in and out . I've seen the seal somewhere .

 

Thanks for all the support guys, I plan on checking those things out. I did just read something that got me thinking... my car originally had the "sticky morning throttle" when I got it. I was reading that there was a bullitin that suggested turning the throttle stop screw in to help "open up" the dirty gummy throttle. Maybe this was done on mine? And since it's all clean the physical gap is too big, letting in too much air at idle?