Depends on what you mean by "jumping".
The commonest interpretation is one or more cylinders
firing intermittently (assuming a petrol engine).
In which case remove and inspect the plugs, they may be bridged by
black oily carbon deposits
If the plugs are clean and light brown/tan then get the HT system
checked, what needs checking depends on the year.
Apart from the plugs, which are a good guide to engine
problems and poor running, HT problems can cause
jumping if the plugs aren't firing, or at the wrong time.
If the engine has an ECU then there are some essential
sensors, and a few less essential sensors.
The main sensors are the oxygen/lambda sensor,
the air flow MAF or MAP sensors, the
crank position sensor, and the throttle position sensor.
These drive the fuel metering and ignition system.
what does ecu mean?
my car is a 2000 model, i changed spark plugs and was running fine but its
started jumping again the other day. if im parked up with engine running
the rev metre slightly goes up when it does it
Engine Control Unit - an electronic processor unit
that takes its input from several sensors and
its output meters the fuel and plug firing (ignition
lambda (oxygen) correct mixture sensor.
airflow (needed to determine fuel air mixture) MAP or MAF
being Manifold Absolute Pressure and Mass Air Flow respectively.
inlet (ambient) air temperature
engine temperature (has it warmed up)
Condition of the plugs tells you a lot about the engine and how it
The first 3 sensors, crank, lambda, airflow are the most important,
if any of these is on its way out you will have problems.
The two temp sensors won't stop you getting home, or
the engine running after a fashion, but if faulty need replacing.
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