I’ve got a 1988 Sovereign with the 3.6L engine. Ever since I’ve owned it,
I’ve had trouble with intermittent stalling and rough running.
Here are the symptoms:
- Never stalls from a cold start.
On a cold start, the ECU is not looking at the oxy sensor…
- After running for 15-20 minutes, it usually begins to run roughly -
After the engine is warmed up, some extra things start happening…
ECU in closed loop,
EGR system enabled(if equipped, your car does not have it)
Evap system sucks fumes out of vapor recovery system…big vacuum
leak could cause problem…
though sporadically when it does begin to run rough.
3. Particularly kicks into “rough running/stall mode” upon
turning a corner
or a change in speed, i.e. letting off the gas pedal and braking.
Maybe a connection that is disturbed by the engine moving in its
mounts…more likely, water in climate control system getting into
- But, sometimes it will go all day without running rough or stalling.
Here’s what I’ve done so far:
- Changed plugs
- Replaced distributor cap and rotor.
- Cleaned out fuel tank (clean as a whistle, which makes me mad
as I did it
- Replaced fuel filter
- Replaced throttle potentiometer (though I metered it and it
my problem is intermittent so…)
A good idea…
- Replaced fuel pressure regulator
- Metered MAF and it checks good
What does it measure at hot idle, and at full throttle?
How did the connections look?
- Idle speed is correct
How did you set this(and the tps)
I know that Jaguar issued a tech service bulletin in the early 90’s for
“Stalling in Turns” or something to that effect, but I can’t get
my hands on
it. Every service center I come across wants to replace the ECU - but I
don’t like that idea, and don’t think it will fix the problem based on the
Very unlikely to be an ECU fault…
Any help would be greatly appreciated.
1988 Sovereign, 1991 XJS V12
Here are some things to check…
Coil…look for signs of tracking on the ht tower.
Make sure the plug wires are not resting on anything, or contacting
the engine…check the wires around the ignition amp and coil, as well
as the actual ignition amp connector.
The low voltage wires should not be near the high voltage
Transmission fluid level…low fluid can stall engine!
Inspect ECU connections for moisture.
Check the ground connections at the intake manifold stud.
Check the coolant temp sensor hot and cold…
Cold reading should be about 5900 ohms at 32F(0C) and 250 ohms
You can also measure the vacuum reading on a hot engine at idle.
At sea level, it should be around 19 inches…
The base idle speed, and tps settings are quite important
in how the engine reacts to varying loads…
The base idle speed is supposed to be about 600 rpm, and the iscv
is supposed to be able to increase or decrease it from there, to
compensate for various loads on the engine from the power steering system,
the alt, and the ac compressor, as well as changes in engine temps…
Have you ever tried just turning the steering wheel at the approximate time
the engine would stall, but without moving?
Its possible, if the base idle speed is off, or the iscv
(Idle Speed Control Valve)is not working correctly, that the extra
load on the engine would be enough to stall it.
I would also suspect a vacuum leak…maybe in the vapor recovery
system. There is a big vacuum line off the bottom of
the intake manifold that runs to the recovery tank in the left side
spoiler…there is also a smaller vacuum control line that runs down there,
and all sorts of valves and hoses that can be rusted up or split.