3.9 high idle and possible vacuum leak?

BDM

Well-known member
May 23, 2005
333
30
OR
Newly acquired 89 RRC 3.9 with new heads, hoses, etc. Hard to start when cold and idles very high ~1800 rpm whether engine is hot or cold. Doing some research it sounds like timing could be off, vacuum leak or temp sensor.

Looking around engine bay tho I found this piece under the plenum without a hose. Anyone know where this would go and if it should be attached to something?

TIA

B80D76D1-69D4-410E-9CBB-25B81EAD6323.jpeg
 

p m

Administrator
Staff member
Apr 19, 2004
15,617
837
58
La Jolla, CA
www.3rj.org
There should be another port - it is for the throttle body heater. Depending on where you live, it may be important.
There usually are two coolant hoses going to it. Removed hoses most likely mean it was leaking coolant.
 

BDM

Well-known member
May 23, 2005
333
30
OR
Ok thanks. Truck came from SLC so you’d think that was important but I guess isn’t the cause of my high idle. Would you have a picture you could send of where it should connect? I don’t see any signs of leaking coolant…
 

Flyfish

Well-known member
Oct 29, 2004
1,402
212
52
St. Louis
There are two throttle body heater outlets that go to two outlets on the radiator that provide warm coolant circulation. The WSM has a routing diagram.