yesterday i spent more than an hour in a traffic jam. Engine at minumum rev and start and stop every 2 meters. Sometimes, i put the gearbox in neutral to leave the foot from the brake.
I noticed that in neutral the minumum of the engine in not perfect as in drive, is like sometimes looses a spark ignition , while when i am in drive is smooth as silk. While i was in neutral for more that a minute, the engine light went on. i did not noticed any difference in the engine performance . After a few minutes i decided to turn off the engine of and restart it. The engine light went off and it did not light again… do you think is a clogged lambda sond?
Andrea - this seems to be normal for our Jags. I suppose because of the transmission load on the engine whilst in drive the idle is smoother and the engine RPMs are ~50 to 100 less (625-650 in drive versus ~700-750 in neutral).
After the check engine light came on and after shutting off the engine did you check the VCM for a code before restarting?
Andreal …
According to the Haynes manual your '92 model stores fault codes until you erase them …
Did you check for any stored code as Mike suggest ?
On the 94MY (probably the same for 92-93MY) there is an easier way to clear codes and not affect the radio (security code and presets). With the key in the ‘on’ position remove fuse #9 (violet 3 amp for the instrument pack) located in the center console fuse panel. Wait a few seconds until the speedo / tach needles drop then replace the fuse.
well the VCM does not show any message. Maybe is not working by itself 
how i check if it is working ? when i push the vcm button with engine off and key turned to show the lights on the dash the mileage goes off (but i have no vcm messages). Now the engine light is off anyway i have drived the car this morning without any errors
To verify onboard diagnostics is working, wth key off disconnect the connector from the coolant temperature sensor:
The sensor is screwed into the thermostat housing and has a two-wire connector, not to be confused with the coolant temperature sender nearby that sends a signal to the coolant temp gauge and has a single wire. Start the engine and the check engine light should be on. Shut off the engine and check the VCM; you should have a code 14. Switch the key off, reconnect the temp sensor, and clear the codd by pulling the fuse in the center console as described in my previous post. **
Mike i confirm that the VCM works , after disconnecting the temperature sensor , i had engine light on, vcm told me the code 14 fault. But, after reconnecting the sensor the engine light went off and the fault code disappeared without removing the center console fuse.
With my 1992 there are at least two codes that do get saved such as fuel fail 37 and fuel fail 39. These are EGR related faults I would get on occasion and I would disconnect the battery to clear them. My car has an aftermarket radio so I didn’t have to worry about about security codes. I ended up putting a battery cut off switch in to make battery disconnect easier. I did this mostly because I often go a couple weeks without driving the car and I wanted to not run down the battery. Quite coincidentally I’m sure, I haven’t seen those faults since installing the switch. But then they never have been frequent. I’ve also not seen any other VCM codes to know if all codes are saved.
i have a battery switch too. On old cars it’s better to disconnect the battery when not in use for long time. I am very afraid of short circuits and fire, i had a car that caught fire in my garage. Was parked 3 days before and there was a short circuit in the engine bay. So better disconnect the battery… we loose only clock and radio code…
That’s good advice… and a frightening story!
it was an old Fiat X1/9 , i drove it for years without problems, one day i parked in the garage near my Lancia Fulvia Coupe and Alfa Romeo Giulia GT Junior and Fiat 500. In the morning we saw a black cloud coming from garage. When i arrived the car was in fire in the rear from engine bay (it’s a central engine coupe). Fortunately fire was not yet spread to other cars and i managed to estinguish it with a powder fire estinguisher, then firemen finished the work. I managed to save the car because the tank fuel was intact. 3 years of restoration and then it was on the road again. i found that a electric cable shorted and start fire to the plastic nearby. On vintage car i always bring an estinguisher on board. ITS mandatory.
Andrea …
You mentioned that the VCM doesn’t show any messages … “maybe it’s not working by itself”
With the ignition on (with or without the engine running) if you push the VCM button does it cycle through a pictorial of all the monitored systems ?
Grooveman, i have no the pictorial vcm but the 92 style, just messages in the small display. Yesterday i tested the vcm by removing the water temperature sensor cable, the engine light went on and the display after pushing the vcm button showed the code 14 error, so the vcm does work.
I noticed that if the error is not present anymore (when i attached the temperature sensor cable again) the engine ligh went off and the vcm did not showed the error anymore. So it does not store the error until the battery is disconnected.
Today i had again the engine light on. This time i managed tò check the vcm and It was a fuel 14 error. So ita related tò coolant temperature sensor. It occurs seldomly and when i turni off engine and start again the light goes off, so i suppose It can be a not perfect contact in the sensor connector. I Will try tò clean the connector with Electric contact cleaner
It could easily be a connection issue, but if not, coolant temp sensors are very affordable and can be changed in a matter of minutes. I always keep a spare in the trunk.