As I started my 2007 jku today getting off of work, My rpms plunged and I heard sort of a grinding noise. Thing is, it drove fine this morning, and idled fine on lunch break. I checked vacuum lines and they all seem fine, I noticed the rpms hang if I rev it. When they drop they go to about 500rpm I need major help diagnosing it before it gets worse. Did I mention I bought it 5 days ago? I gently drove it home and have been scratching my head since. Any help would be beyond greatly appreciated. T.I.A

 

HI, Welcome to JKF.. Some questions.. are there any warning lights on? Check Engine? Where did you buy- dealer or private sale? If any lights are need to get diagnostics for codes - many auto parts stores can read the codes.. then you can look up .. Google.. How high are you rev'ing the engine and how long does it "hang" at what RPM. I do not have a 3.8L ; however, many members here do and are more familiar with the throttle FI system on that engine. I am confident that more replies will be forthcoming.

 

I bought it from a private dealer I suppose you could say. There are currently no Check engine lights on. I normally keep my rpms while driving at 3k or below,3500 max.

 

Curious if you had any further progress on this? When you drove it home did it run OK? Did you check for codes?

 

It ran fine as far as I know. I haven't taken it far. There is no C.E.L so I would assume there were no codes it just sketched me out. As I still am slightly sketched but I guess I'm just gonna send it. I'm not entirely sure what it could have been. Wasn't a throw out bearing tap/rattle either. Though it does have the rattle.

 

3.8's (at least mine did when it was 3.8) hang like that and take off when wheeling going down a steep slope EG 1000rpm L2 gear and one touches the throttle just a hair and off she goes up to 3500+. Have to brake to get it back down. It is something to do with throttle ramp down for emissions - stupid, stupid idea whoever thought it up. Chev engine fixed my problem.
Not sure what that grinding sound could be. Even may be exhaust issues rubbing, rubber support grommet going/gone. Engine pulleys, belts, PS pump, alternator, loose heat shields etc. Start with simple stuff first. No CEL are a good thing.