2.9l idles then revs itself to 2k and then returns to idle?

[kuivinenj]

i have and 89 bronco II that when i fire it up idles for a minute then revs itself to 2k and then idles again and will do this randomly as long as i let it idle... if i drive it however, then let it idle it will do so normally for about 10 minutes then it will start to rev itself randomly again... any idea what could be causing this?

 

[kuivinenj]

well figured out that when it revs itself to 2k then the check engine light comes on (didn't see it before because check engine light was burnt out) and then it drops to an idle then the check engine light goes off and it revs up again i ran the codes and they say its running rich but what causes that ?

 

[sirfunkeybut]

o2 sensor? or i would guess the IAC valve

 

[Gary101386]

take off your iac and clean it... mine was doing the same, now its all good...

 

[robertc1024]

There are a few things that can cause them to run rich.
1. The fuel pressure regulator. Pull the vac hose off of it and smell it to see if it smells like gas. If they take a dump, they can also fry your brake booster.
2. Ground wires. A lot of people have had issues with IIRC, an orange one that goes from the passenger side head to the fire wall.
3. Coolant temperature sensor. Mine went bad and it made it run rich as hell.

Sounds more like the IAC to me though.

 

[kuivinenj]

ok i cleaned IAC good and it still does it just not as much... going to just replace the ATC and temp sensor for the hell of it there cheap enough and im gunna check that ground tomorrow, hope one of those fixes it, and thank for the info

 

[Gary101386]

i would say replace the IAC. if you cleaned it and it got better, my money would be on the IAC.

 

[kimcrwbr1]

Disconnect the neg batt terminal for 1/2 an hour to reset the computer whenever you change/clean a sensor. Then run it for around 20 minutes at medium speeds to set the new values. While your buying parts put in a new PCV for giggles. Replace any hard or cracked vacuum lines.