I have a 2004 Discovery II SE7.

In June it went in to the dealer for a 105k service. Immediately afterward it had a slight miss at idle immediately after start, and a distinct whining sound like a pump spinning up that went away after about 2 minutes (you could hear it wind down as well). The misfire has gotten progressively worse, and about a month ago for the first time it ran extremely rough and the engine light came on. I thought it might be fuel and used some Startron and the truck ran normally for a couple weeks, engine light went out. I drove over 1000 miles and then once again the car ran very rough at start and the light came back on, this time 3 days in a row. Added some gas line dryer thinking it could be gas again, and the truck ran well for a 800 mile week-long trip. Got back home, and now three days later (all normal driving) the truck again rough at start and engine light illuminated again.

On the phone the dealer suggested a small coolant leak into a cylinder. The coolant levels are constant though and the oil is fine.

I don't have the codes but will stop and have them read.

I'm trying to recall the weather, it could be that the truck runs rough after rain, but I'm not sure. That was the case this time, but before....?

In any case, any wisdom would be appreciated. The truck has been regularly serviced and has had no problems over the 20k+ miles I have put on it since I bought it. What is frustrating is that it will barely run at start, then run normally after 10 minutes of operation, run fine for several weeks of driving, and then again run rough at start and set the light off. And of course it was running fine before the 105k service, and while not causal I always hate it when a truck runs worse after a "service."

I looked through a bunch of threads to see if I could find an answer and didn't see anything, but apologize if this has been addressed already elsewhere.

Thanks!

 

This sounds like the Secondary Air Injection Pump. It is located on the passenger side of the engine bay, near the firewall. NA spec calls for 76 seconds of operation at start up in a specified ambient temp range (over 40deg F IIRC). The increase in noise may be caused by:

1) failing bearings in pump
2) pieces of the pump filter clogging the pump
3) malfunctioning solenoid
4) malfunctioing SAI valve (two total)
5) worn rubber mount bushings on the pump allowing excessive vibration.

Sorry, can't help on the other problem; but the others will say: "Bring us the OBDII codes, then we'll talk."

 

Thanks, that is where the sound comes from so I will check it.

The OBD II Code is P0304 Cylinder 4 Misfire.

What is frustrating is that the truck sat overnight and then ran rough and the light came on at 8 am, it sat all day in pouring rain until I started it at 3 pm, at which time it ran fine.

I'm thinking new plugs and wires?