XJ40 - Replacing the Temp Sensor and IACV Idle Air Control Valve

[@Teeveepicksures]

I really thought you were gonna say since it was Lucas that it came with a spare sensor. 😂

[@JCTsFascinatingHobbies]

LOL!!!!!! It's always worth having some spares!!😂

[@jimmya2578]

Did you do a “hard reset” on your ECU (i.e., disconnect battery for a couple hours then reconnect), after installing the new parts? Just curious - I am about to replace the ECT sensor on my ‘92 XJ as well.

[@JCTsFascinatingHobbies]

I did, the battery had been disconnected for several days before replacing the sensor.

[@Kalgt]

Hey. I have a 1989 XJ40 3.6 and am stumped trying to fix my rough idle issue. During a cold start, it idles very lumpy at aroumd 100-200rpm and will stall unless I apply throttle for about 10 seconds. Warm starts are fine. I have a terrible missfire too, which is also very aggressive between 2000-3000rpm with moderate throttle pressure. I have done the following things, all of which have not made any difference: • all spark plugs (oem spec champions all gapped correctly • ignition leads • distributor rotor • distributor cap • ignition coil • ignition amplifier • idle air control valve • coolant temp sensor • checked for vac leaks • removed and cleaned throttle body / pipework / pcv system • MAF sensor • fuel filter • tested injectors, all working fine • fuel pressure reguator • fuel pump I have yet to replace the crank position sensor as i am struggling to find the fat connector type. However if im not mistaken, a faulty CPS wouldn't let the car run at all? Thanks, Kallum

[@JCTsFascinatingHobbies]

A Faulty, completely failed CPS would stop the car running. However, because the tip is magnetic, it can pickup all sorts of metal filings which would impede the signal and potentially cause a loss of signal, even momentarily. I'd be tempted to remove and clear it first. There is also a throttle position sensor, mounted under the throttle body, which may cause issue and might be worth replacing. Another thing to check, air leaks. If you use some brake cleaner and spray it onto the intake and associated rubber vacuum pipes, whilst the engine is idling (hold the throttle, slightly). Any increase in RPM would suggest a vacuum leak.

[@Teeveepicksures]

O2 sensor?

[@sparklauerei1]

my jag also runs really rough in idle and especially when its warm. i bought it in winter and it wasnt that bad back then. might also buy some new temp sensors and hope it fixes it.

[@JCTsFascinatingHobbies]

The coolant temp sensor would definitely be my first port of call.

[@sparklauerei1]

@@JCTsFascinatingHobbies can i somehow diagnose the coolant temp sensor? I unplugged it once, nothing changed, but i got a fuel fail 14 indicating a missing coolant temp sensor. so can i assume mine is working?

[@JCTsFascinatingHobbies]

@@sparklauerei1 Coolant temp sensors are strange in the way they fail. The ECU is looking for the sensor and looks for outputs within a specific range. When they fail, they tend to fail with the sensor still outputting in a specific range, so, it won't trigger a fuel fail fault code. New ones are not expensive, and worth replacing as part of your troubleshooting.

[@ScaphanNetwork]

Hi you seem VERY experienced in all things Jaguar and electrical. The LCD screen on my X300 has leaked and so I need a replacement lcd screen. Any idea where I can get one??