My '98 Disco has started making a high pitched whine (or maybe it would be described as a whistle) under low throttle, or idle, near the throttle body. It will happen while I am crusing or just parked after things heat up a to normal, but if I hit the throttle to accelerate the noise will stop. I have stuck my head under the hood and manually actuated the trottle, but I can't seem to pin point the source of the sound. Anyone got any ideas?

The engine seems to be running fine, but the sound is really annoying, and sounds like something is wrong.

 

If it is around the t/body, it must be a vaccum leak, I would suggest you use a little carb spray and, only when the engine is cold, start it up and spray small amounts of the carb spray on all the fittilg, seals and hose and when the engine speeds up you will haave found your leak.
Remember small amounts of spray on a cold engine ONLY.
Mike

 

I have a disco 'oo mill.with apparently the same problem,a whine at around 1000rpm that disappears accelerating.I have the impression that it could be accompanied by a slight vibration that appears to come from under my foot but I am not sure.I will check as you suggested for a leak in the vacuum system but I am not entirely convinced.If you solve the problem in the meantimeplease share the solutionand I will obviously do the same.Thanx

 

That sound can easily come from a bad serpentine belt, the belt tensioner or pulley or a failing u-joint in the front drive shaft.
Mike

 

Hi Mike.I checked the serpentine belt but it was OK and the noise appeared to come from the underside of the chassis .So I took the Disco to the local workshop andhave been told thatthe whine at around 1000 rpm is given bythe failing air suspension compressor.I have been told that this is rather expensive as the only solution is it's complete substitution.Have you any tips?Thanx

 

The shop is blowing smoke up your pants cuff --- a failing or weak compressor pump does not produce the noise you describe. A whistle at idle is almost always a result of a vacuum leak when the manifold depression is at its highest ---and will go away with throttle plate opening. However -- opening the throttle by hand when under the hood does not have the same effect as opening the throttle when rolling down the road with the engine under load. Check fora vacuum leakas Disco Mike describes, and also check the hoses going to your cruise control dashpot. It alsomight be a leak on the throttle body-to-plenum gasket on the underside of the throttle body. I've also seen aloose O2 sensor produce a whistle noise more apparent at idle ---masked by road noise when rolling.

regards,

Geoman

 

i get the same whine when at idle, but something that also happens, is when going about 45mph and i hit a bump, i get an insane vibration, so it must be my u-joints. you should check yours out.

 

What year and mileage is your truck?
I would inspect and lube the u-joints and slip shaft both front and rear.
Mike