I have a 99 Ranger that I use for a work vehicle . I just got it last week and I got a few problems that I just noticed . I washed the engine a few days ago and since I did that sometimes I get this deep tone howling noise from the engine , it comes and goes .. when gas is pushed it goes away , when you left off the gas you hear it . I noticed it doing this when sitting still as well . I never heard it before I hosed off the engine . I have no idea what it is !!

any ideas would be great
Thanks

 

a/c compressor clutch is the first thing that comes to mind. Next time it starts doing this , check to see if the heater control is set to off , floor , or vent. Any other position will cause the compressor to cycle.

 

Thanks for your reply , the heater control is set to the off position and it does it . I will try it with it on and see what it does and get back to you.

 

You also might have the dreaded 'belt tensioner / idler pulley gone bad' syndrome which is oh so common.Usually one of them makes a screeching sound , but I've had one do the growl thing too.

 

or try getting a gator back belt cas i did the same thing and before i started changing pulleys i tried a new gator back belt and its fine now

 

Was your engine hot? it could be the cooling fan. that only will come on if it's hot. does it interfere with your driving?

 

This is a little crazy to say, but it was the air cleaner mod I did , removing the snorkle adapter .

Can anyone send me a Ebay link of something for the MAF adapter so I can put a after market filter on it ?

 

Try another IAC Motor... The spring gets weak and they flutter. They act like a wind instrument and can be very loud. To catch it in the act you can unplug it while it's doing it. The engine will probably stall, however you'll hear the noise disappear as soon and you pull the connector.