QuestionHi John. Just bought a 1996 Discovery 1 V83.9i. On starting engine revs to about 2000rpm for awhile then settles to about 1000rpm. When taking off there is an initial flatspot unless I keep revs up. Sometimes rpm drops to about 500 and will not rev even if fuel applied then suddenly takes again. Could this be the Thrittle position sensor.
AnswerHi Wayne,
it's possible that your TPS is causing the problem BUT there are other possibilities too.
For example, if your plugs and wires are in need of replacement, you could be 'flooding' the engine on 'taking off'. Changing out the plugs and wires is an easy job, one that you could do yourself. Make sure you buy Magnecore HT leads and good plugs. A good plug and wire combo is best for these engines.
Other possible causes could be the camshaft position sensor (CMP), the Mass Air Flow (MAF) sensor and perhaps the crankshaft position sensor (CKP - rare but stranger things have happened). From the workshop manuals:
If the camshaft sensor fails, default operation is to
continue normal ignition timing. The fuel injectors will
be actuated sequentially, timing the injection with
respect to top dead centre. Injection will either be
correct or one revolution out of synchronisation. The
fault is not easily detected by the driver. The fault is
indicated by illumination of the malfunction indicator
light (MIL) on North American specification vehicles.
As there is no default strategy, failure will result in the
engine starting, and dying when it reaches 550
rev/min, when the ECM detects no MAF Sensor
signal. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
The crankshaft position sensor is the most important
sensor on the engine. It is located in the left hand side
of the flywheel housing and uses a different thickness
of spacer for manual and automatic gearboxes. The
signal it produces informs the ECM:
- the engine is turning
- how fast the engine is turning
- which stage the engine is at in the cycle.
As there is no default strategy, failure of the
crankshaft sensor will result in the engine failing to
start. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American
specification vehicles.
Some owners have had success by cleaning the MAF and suggest aftermarket MAF cleaners. Be careful using any cleaners, especially around the electronics.
Lastly, there are other sensors that could have an impact: vehicle speed sensor, water, fuel and air temp sensors. It sure sounds like the TPS but its so mercurial a problem to solve. I hope its the TPS - simple to fix and a very common problem. I know for me, the TPS was the culprit and it cost me 000'S$ before I found out it was the TPS. Of course, the dealer did not reimburse us for all those other parts they swapped into the Disco in their vain attempt to 'solve' the problem. hmmmm...
I hope this helps,
JohnMc
