I'm new to Discovery's, just bought a 2003 Disco II with 90k miles. A bit of history; I just bought it from a guy that said he replaced the head gaskets after the car started running rough and misfiring on a couple cylinders.

Ever since I bought it, it has had a rough idle. It's not bad enough to trip a code for a misfire, but it's definitely not as smooth at idle as other Discovery's that I have driven. What should I check first? I've glanced around for any loose vacuum lines, and also noticed that the plug wires look new and are labeled with cylinder numbers (I'm assuming they were replaced during the head gasket service).

Let me know what you think!

 

I'd check spark plugs (pull them and see if the spacing is good), then I'd check the plug wires, then I'd check the Camshaft Positioning Sensor. If you aren't throwing a code then the CPS is probably good, but sometimes you get a lesser CPS that doesn't work as well.

 

Take a look at the fuel trims first. That should give you some direction.

 

Unless it seems to be losing coolant or harder to start after sitting overnight I wouldn't suspect a head gasket issue.

I just had a week-long fight with my Disco II involving rough idle, but I had codes. The codes lied. It was my MAF, which never threw a code. I might have had a cranky crank sensor, too, because I replaced it without a code and got marginal improvement. If you have a code reader, which you would need for fuel trims, be sure to check the pending codes.

 

Is the RPM gauge jumping up and down or is it pretty steady? I ask because a broken motor mount can cause a vehicle to seem like it's running rough when really it's just due to the engine moving due to the broken mount. It can also run rough or idle rough with a bad harmonic balancer.

I had both of those problems with one of my 05 Jeep Wranglers and it was a bad motor mount once and then a harmonic balancer.

If the idle is jumping up and down check for a clean throttle body, clean IAC, bad or maybe plugs that aren't all gaped the same.

 

Same issue here. Replaced MAF. Runs like a new 04 D2 w/ 214,000 miles.