Hi, I have a 99 f150 5.4 and I have a whistling coming intermitently from (i believe) the throttle body area. It doesn't happen at idle but it does on accel and decelleration, sometimes. The engine runs good but does have a slightly rough idle, its not like a miss, because its not consistant. Also, if I have the a/c or heater on at a stoplight the rpm can surge 5o to 100 rpm, then back off slowly. I'm thinking that its just a slow iac that needs replaced... maybe gunked up or just not opening or closing the valve as it should. Seems like a pretty common problem with this truck. Thanks in advance.

 

Clean the IAC and see how it does.

.

 

I had a whistle once, 1500-2100 rpm's, constant though. Turned out it was my A/C pulley, clutch and compressor I believe. Since around then, no more whistle! Another vote for IAC cleaning first though.

 

If you have a whistle, also check for vacuum leaks - those can definitely cause idle issues. Any CEL and/or codes?

 

no, no codes and no cel. I changed all the rotted vacuum hoses i could see about a month ago, checked pcv it seems fine... The only vacuum i haven't changed is the rubber elbow on the back of the trottle body that comes from the pcv... but I can't even get my hand back there...

 

That elbow is a high failure item, but it will usually throw a CEL for lean both banks when it goes. Find a kid with a small hand to get back there for you!