HI all. For several months, my 1993 22-RE truck has had a funny sound coming from under the hood on the left (driver) side. It's a kind of whirring, fluttery sound, or a vibration. Never happens when accelerating or under load... only when idling or coasting, and it stops when i push in the clutch. Sometimes it also surges (not like an idle surge, more like a 2-peak-per second "whir,whir,whir,whir")-- the funny sound, that is, not the engine itself.
Performance otherwise seems about normal--possibly slightly less efficient gas mileage.
A couple of weeks ago i checked the air filter, as i live on dirt roads and often they get dirty enough to shake off and replace without buying a new one. It was quite clean but: there was a mouse nest about the size of a grapefruit in the flat air space below it, and about a fifth of the filter was chewed clear through in a big hole.
So i threw out the nest and was real proud of myself, thinking the air filter would still be doing about 80% of its job, and at least there's not a big mouse nest blocking things.
But the noise continues, and i started to wonder: What if air just comes straight through that hole into the engine, and that's the whirring sound i hear, and having 20% of a filter gone-- not blocked-- is about as bad as having no filter at all, because straight unfiltered air (dusty) can come right into the engine and ruin parts?
So the questions are:
1. Do you all think the air filter hole could cause the funny, high, whirring noise, and
2. Should i order an air filter online and not drive anywhere until i put it in, or can i carry on until my next town trip (about an hour and a half away, over sometimes dirt roads)?
THANK YOU!
~LauraStillLuvin'HerLilTruck

 

Lots of engines run without air filters, but they just don't run as long or as far. I'd only drive in nice clean air before getting a filter in, and avoid driving if you can.

As to the noise, maybe you've a piece of "something" (filter parts, nesting material, dead mouse baby?) stuck downstream. I'd disassemble all that you can easily and go hunting. A borescope might be nice for some of this as well. But first....put in the new filter and check the sound. The filter will also filter some of the sound from the intake system so it should be quieter with a real filter in place.

 

Thank you, Blueman. That's a good point about maybe something being stuck and causing the whistling/whirring noise. I will get the filter first thing when i go to town on Friday, and try to make sure not to drive behind another vehicle on the dirt stretches.