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diagnosing the throttle body?

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Old 03-22-2011, 11:54 AM
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Default diagnosing the throttle body?

OK gang, my 99 VDP died on me the other day and I suspect it may be something wrong with my throttle body. About one week after replacing my fuel pump (thanks to this forum and some very good videos I found linked on this site), the car died on me. I first noticed that it quit responding to throttle inputs and then, over the next 15 or so seconds, the RPM's dropped and it finally stalled. Upon restart, it would occasionally stumble to life for several seconds, but at extremely low RPM's and sounding very rough.

I had it towed to my shop where I checked that I have fuel pressure at the rail, so the new pump is not the problem. I noticed that when the key is turned to the on position, I get a weird electrical humming noise coming from the throttle body. I had not noticed the car doing this before, which leads me to my questions... It the throttle body a know weak point in these cars, and is there a way to diagnose the the throttle body to confirm if it is functioning before spending the $$$ on a new one
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Old 03-22-2011, 05:19 PM
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Hearing a hum from the throttle body is not unusual, you have probably just got sensitive to it at this point.

Yes, there was a recall on the '99 MY throttle body found in Service Action S514. It called for a replacement of the TB for some VIN ranges, reflashing the ECM for others. If the recall was preformed there should be a decal added to the driver door 'B' column. Unfortunately, the repair authorization expired at the end of '09.

The Service Action specified that dealers contact the owners for this repair and check for the work being done for any car in for repair. If you can document that the car was in a dealer service department before the expiration of the SA you might have a argument to have it done. Jaguar will only preform the recall work once.

But that may not be you issue after all but your symptoms match those reported on the recall. Any CEL codes?

Here is the SA document.
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File Type: pdf Jaguar Service Action S514.pdf (312.3 KB, 284 views)

Last edited by test point; 03-22-2011 at 05:22 PM.
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Old 03-23-2011, 03:27 AM
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I have a whining sound from the TB stepper motor when ignition is turned on and engine not running.
So this could be normal.

To check if the TB is responding, remove intake duct, look at the butterfly.
It should be fully closed when ignition is off.
Now have someone turn the ignition on (no starting of engine) and have a look at the butterfly.
It should open a little bit when ignition is turned on and you will hear the sound of the stepper motor.

Also, with the ignition on (engine not running) the butterfly should move (open) as you press the pedal and close when pedal is beeing released.


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Old 03-23-2011, 01:19 PM
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Thanks, I'll check it out this afternoon and report back
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Old 03-23-2011, 03:54 PM
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The butterfly should move SMOOTHLY with throttle pedal position - any jerky movement implies that either the pedal position sensor, throttle position sensor or throttle motor signals are intermittent... a simple unplug, cleaning the connections with contact cleaner/lubricant (like from Radio Shack) and reconnection may resolve the issue. A little dielectric grease around the connector's o-ring can help prevent future problems.
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