Idle speed bouncing up and down

[imq707s]

I've got a 97 Mountaineer with the 5.0 v-8. I just started noticing that when I'm stopped at a light with the radio off, I can hear the rpm's going up and down. I can barely see the guage moving, but it definitly idles up to around 800rpm's and then down to around 600rpms. It does it in neutral and drive, with the AC off. It idles up to 800 and then about 5 seconds later back down to 600, and it keeps repeating that pattern.Could a EFI sensor be going bad? Which one?

 

[Maniak]

Every time I get that symptom (had it on 3 different fords.. w 3.0 liter motors.. and on our 4.0 in the explorer) it is either the TPS is bad or the Idle Air Control valvle (the thing that lets some air around the Throttle Body to control the idle).

I'd start with those 2 items first..

~Mark

 

[sirhk100]

Something like this?

Sorry, just had to do it!!

 

[RTStork]

Ive had good results by cleaning the MAF. Just an idea. Its easy to do. Clean it with rubbing alcohol and a Q-tip.

 

[Doug]

my bronco II did it and so does my 4.0 explorer. Ive cleaned the IACV and the MAS but that didnt fix it but you can try doing that. Im pretty sure i need a new IACV it makes a high pitched humming during hot weather.

 

[01EB5.0]

Yeah, both of those problems are most lilely bad IAC units. They are about $95 from fordpartsnetwork.com
good luck!

 

[Shane91Explorer]

Clean out the IAC valve.....

I've dealt with this problem many times on Mustangs. All I do to fix it is take the IAC valve completely out (only two bolts hold it to the TB on a Mustang, I'm not sure about the "X"). Take the Solenoid off of the valve (two srews), and spray the hell out of it with Carb Cleaner. Push the plunger in and out to free up the carbon build-up inside. I do this every year as summer maintenance now, and it always idles perfect.

Let me know how this works for you. I know a few other fine tuning tricks for the 5.0 that may help you as well.

Shane