These are 24V PID addresses for use with the OBD2 software and
reader - other engines may differ.
The nearest approximation of the conventional 'Choke' is OPEN
LOOP when the HO2S sensors are cold, but they have heaters in them
to bring them up to temp very quickly - when the PCM switches to
CLOSED LOOP the engine itself is still quite cold. If you block off
the Idle Air Bypass Pipe at this point the EECV cannot maintain the
engine idle - combustion is too fragile. However, once the engine is
at full operating temperature the programming can maintain idle by
varying the spark advance and the pulse width - the heated cylinders
are much more amenable to these adjustments. Blocking the bypass
pipe like this is just one demonstration of how powerful the
and how it can maintain engine function under quite extreme
Because engine control is holistic, the chances of an EEC-V
controlled idle being effected by a dirty IACV is probably 10 or 15
to 1. It is always worthwhile cleaning it on the EEC-IV 12v
variant where this was quite common, but much less so on the newer
engines. Experience shows that a failed IACV normally causes stalling
rather than a poor idle.
So, if you are experiencing a poor quality idle on your 16V or
24V engine then the following order of diagnostic work should be
1. An air inlet leak causing unmetered air to enter the inlet
manifolds. These can be split or disconnected vacuum pipes, a loose
EGR pipe, faulty EVR, split/loose air bypass pipe, split inlet O
rings especially after disturbing the inlet system. In particular
there is a plastic vacuum T piece located underneath the central throttle
body of the inlet manifold which is very prone to failure (Two of
the Ts are 4mm and the other is 6mm) and is no longer available so
you may have to make your own replacement if this has fractured.
system, loose or faulty petrol filler cap. Make sure the filler cap
is ratcheted tight.
3. Lost TPS position. Check for P0122 TPS Sensor Circuit Low,
and on the DATA page check the % figure for the TPS. Static the TPS should show
16% approx. If the reading is lower, then the EECV has lost synch with the TPS.
Fuelling will be poor, idle effected by lurching or surging. On autos, you may
also notice that the gears are being selected with a thump, both when
stationary and on the road. If the DTC and the percentage reading is seen then
force a resynch by disconnecting the battery for half a minute. Don't
forget the radio codes before you do this, however. After the initial poor
running while the running parameters are relearned, the engine idle and autobox
changes will be greatly improved.
4. A 'Hanging throttle' - engine delays at higher revs when accelerator is
released, then revs die suddenly, revs stick high and engine races irregularly
without touching the accelerator - is probably caused by a sticky throttle
butterfly valve, particularly on the DOHC models. Grime and burnt oil (from the
PCV system) can gather round the throttle plate and cause it to stick slightly
open. Clean the inside of the throttle body with good quality carb cleaner and
an old toothbrush.
5 . Faulty connections on or flatlining upstream
Sensor. These are the ones located on the engine side of the
Catalytic Converter - those after the Cats do not affect engine
6. Faulty MAF.
Where the element or conditioning electronics has failed a MAF will not produce
a meaningful reading to the PCM. This will result in a surging idle, and
probably also jerky, thumping autobox gear changes and a P0102 Diagnostic
Trouble Code. The MAF will show typically 0.000 to 0.005 lbs.p.m. at idle
Where the element is failing or corroded the MAF may show too high a reading. This drives
the Long Term Fuel
Trims too lean. This is detailed on
7 . Faults with the Ignition modules or
wiring (on 16V engines in
particular), but the EI module on the 24V has been known to split at the rear.
8. A slightly racing idle may be noticed on occasions
when the petrol tank is nearly empty. Idle is corrected when the vehicle is
next filled up and this is not a concern. However, a persistently high
idle, surging or racing, allied with thumping into gear [autos] or dragging on
the clutch, bulking in reverse [manuals] then see (3) above.
9 . Quite Rare -
incorrect installation of the 24V camshafts during an engine
rebuild. It has also been known with the 24V for the cam
chains to jump
sprocket teeth when the timing chain has become very badly worn.