Land Rover Repair: Check Engine light, throttle position sensor, problem surfaces

Question
Hi John,
         Yesterday while I was driving my 1997 Discovery, I experienced some problems with the emission. The vehicle was accelerating and then cutting off and then the Check Engine light started blinking. Do you have an idea on what the problem might be. I had a similar problem last year and had to get the fuel injectors replaced.

Thanks,
Siddharth

Answer
Hi Siddharth,

here are some possible causes:

TPS - the Throttle Position Sensor can begin to fail and cause sporradic rev's and rough idling.

On some 4.0, 4.2 and 4.6 engines (mostly 4.2 and 4.6) the exhaust valves have been known to stick due to a buildup of carbon combined with some other substance (not too sure what).  Regardless, the outcome is that the exhaust valves begin to stick and thus driver will experience power loss, a sensation of the engine missing, misfires and stalls.  This begins to surface at about 50,000 miles.  The only fix is a valve job (about $2000 US).

It could also be the spark amplifier module or the coilpack (or coil).

It depends on how many miles you have on your Disco.  High mileage and any of the above could be the cause.  Low mileage and you should look to fouled lines, bad fuel, old fuel filter.

If your problem surfaces when the car is at its normal operating temperature, it could be the valve problem I mentioned.  

Have a local mechanic check your ignition system to determine if you have a fouled wire or plug.  I've seen problems like this when the coilpack begins to fail. The only way to tell is to hook the engine up to a diagnostic machine and run it until the problem is trapped.

Did you see any error codes on the OBDII under your passenger seat?  Its a small unit about the size of a box of crayons or a man's wallet.  Turn the ignition until just before the engine should start.  While on, take a look at the OBD display and let me know what codes you see, if any.

Best of luck,

JohnMc