My 2004 Discovery is clunking when I lift my foot off the gas (sounds just like backlash in the transfer case). It only happens about 10% of the time. Does not seem to be temp related. Sometimes happens a second of two after you take your foot off the gas, in fact I thought it was related to the brake light switch but no. It always happens below 40mph, never at FWY speeds.

At cold startup the engine revs up and down between 750 and 2500. I placed a restricter between the air control valve and the intake manafold and that fixed that problem and got rid of the P0171 and P0174 codes but I removed it because of a lack of power (codes are back).

I replace and tested all the small vacuum lines.

A couple months ago I replaced the coil packs.



Trouble codes: 0300, 0307, 0305 at start up. Pending codes 0171, 0174

I ordered new plug wires

 

I have the same clunk and after replacing front prop shaft I just figured it was part of the AWD drive-train.

 

As for the clunk, As long as it isnt a horrendous clunk or recently gotten way worse, it's probably normal. Theres a fair amount of slack between the moving parts that make up the driveline. Theres a lot of moving parts to an all time, all wheel drive line and the tiny amounts of slack/clearance between each mating part adds up accross the whole system to a fair amount. If I release my throttle abruptly when the truck is under accelceration or "jack rabbit start off" I too hear a clunk as well. I Have ever since I bought it. When I reserched it for myself I figured out that I needed to learn how to let off the gas pedal and get back on the gas pedal with a little more finese. These trucks are not engineered by Japs, lol. Try changing your driving habits in this aspect and see if it gets better. If not I'd start looking into it more deeply. Axle/differentials is where I'd start. Just a simple fluid consistancy evaluation would most liklely give you an indication if something is going on in the differentials. (excessive Metal shaving on magnent or milky appearence in gear lube) But the driving habit change worked for me for over 60,000 miles now.

As for the idle problem, i dont know what the codes relate to, one of the more advanced members will chime in on that soon i'm sure. If not you can look them up on here, but it sounds like you may need a MAF sensor or something. Maybe just a good throttle body cleaning. They get pretty dirty on the inside and dont operate as smoothly as the should. Very Easy do-it-yourself job there. Just a can of carb/choke cleaner and 1 or 2 tools to get to it. Also check for leaks or holes in your air intake hose AFTER the MAF sensor and patch with tightly wraped electrical tape if you find any. If the engine is getting any air that it doesnt know about because it entered the system after MAF it would it would cause some idle issues.

Of course always start withthe cheapest or even FREE interventions. Never just start throwing parts at the truck. That can get expensive quick like!

 

This clunk does not happen all the time. Only about 10% and sometimes a second or two after I release the gas peddle. It almost feels like the trans is downshifting or the torque converter is grabbing. Also, it just started a few hundred miles ago. If this were backlash in the drive train it would, I think, happen right at the time the pedal was released.

 

How many miles are on this Disco? I see you have one of the ever so sought after '04 models, so I'm guessing it's pretty low milage.

If it's shifting out through the gears as good as always I wouldn't suspect the transmission, but it never hurts to check the fluid level. Maybe it's just low enough to cause the T converter to act up a little.

Also since you have the Center Locking Diff you could remove the front drive shaft and drive it a day or two and see if it goes away. If not put the shaft back in and remove the rear shaft and drive it a day or two. That would help you isolate the problem area a little more definitivley.

Without that CDL you couldn't do that last option I mentioned.

 

My 99 does that Clunk. Always has especially if I let off while it is shifting and push on the gas. The 04 does it occasionally ,but i drive it a bit differently than the 99

 

Like I said if it's not just horrendous or progressivly getting worse, you're probably on a wild goose chase my friend. Just normal Rover symptoms.

 

Interesting to see that others have the same problem. If I can't trace it down myself I am going to take it to a trans shop here in SoCal. When they find out what it is I will let everyone know. I THINK it is some valve or vacuum line that controls the trans???? I will check the fluid level. It is bad enough that I think it is going to damage something. It has 122,000 miles, very little off road time. We are headed to the local mountains tomorrow and see if we can find some mud and snow to play in.

 

Great! Let us know if they find anything.

 

That clunk is the sum of the backlash in all the drivetrain components. I was worried about it and I thought it came from the rear diff. I nagged the dealership for months about this cause the Disco was still under extended warranty, until one of the mechanics there took me aside and told me not to worry and that he would personally rebuild the rear diff if it failed. Two years later the clunk hasn't changed and the both diffs and transfer cases are still running great.