Stalling and rough idle

Chris Baker

Well-known member
Sep 12, 2019
Bolivar, Tn
I have an 04 Discovery II 4.6. Long story short, the original engine was cracked so I had to put in a used engine. Had it back for about a month and have been working out a few running issues. I have replaced the spark plugs and wires. It was still idling rough and seemed to be sluggish in response and power once up to speed and on the road. As of yesterday I replaced both down scream O2 sensors and the MAS senor. When we started it, at times it wants to go dead within a few seconds but if you give it a little gas, you may can get it to idle around 700 rpms. If you get on the road, it seems to run OK but once you slow down to make a turn in a parking lot, etc, it will stall out.
Today, I disconnected the intake hose from the filter housing and covered the end of intake hose to restrict the air flow. When I did that, it idled up and smoothed out.
This leads me to believe it may be running a little to lean, What do any of you think? I wonder if I have a bad idle intake valve.
Last edited:


Well-known member
Sep 12, 2018
You'll need to get a decent OBDII reader and get the codes, otherwise it's tail-chasing time.
Probably worth it to invest in a LR specific reader. If you get a cheapy, you'll realize why it's a cheapy and end up with one you should've bought in the first place.
There are several threads on which one people like. Everyone has their favorite.


Well-known member
May 24, 2007
Boise Idaho
X2 on the LR specific scanners for this problem as well as others you will encounter. At the very least a generic scanner with live data would be more helpful to figure out what is going on. Could be your IAC or a vacuum leak or something else. You can throw parts at it if you have some laying around but at some point your going to need a scanner sooo, might as well get one and reap the benefits now. Good luck