Hi - My car is starting fine when dead cold or fully warmed up. In between it acts like the fuel mapping is all wrong - it will barely start, not idle, etc. until it is fully warmed up, at which point it goes back to running / starting fine. Ignition amplifier is also a new unit.

Vacuum to the ECU is good, the engine temperature sensor (for the ECU not the gauge) is new, the throttle potentiometer is also working correctly and properly adjusted. We also replaced the o2 sensors and made sure they are properly grounded.

Any suggestions as to what other sensors to check or replace that could influence this?

This is an '86 5.3. Thanks!

 

Two questions:
If you start it when warm, can you hold it running on the throttle?
If when warm, if your foot is on the floor when starting, does it start better and can you then hold it running on the throttle?

 

Hi.

"If you start it when warm, can you hold it running on the throttle?" Yes. It sputters and does not run smoothly, but it will keep going.

"If when warm, if your foot is on the floor when starting, does it start better and can you then hold it running on the throttle?" I have no idea - I never touch the gas when starting the engine.

 

Number ONE item on any V12 with that attitude.

Change the CTS (Coolant Temp Sensor), just aft of the B bank thermostat housing.

CHEAP, even in the USA, and NOT unique to Jaguar.

ALSO

Check VERY CAREFULLY the integrity of the sires inside the rubber cover, and the plug, they can fail, but usually a DEAD V12 is the result.

If you have not done so yet:

Clean the 2 throttle housings inside bore.
Unplug and CLEAN (Lemon Juice) the Resistor Pack Multi Pin Plug.
Check and adjust the TPS setting.

My $$ are on the CTS only due to the Warm Tempi issue, its having a female moment.