Rough Idle-Muffler??
 

I just had valves adjusted and my 84 300 D still has rough idle. While at the shop for valves, my mechanic informed me that I need a new rear muffler. Could the muffler cause the rough idle??

Thanks,
Harry

You sure it's not just change of muffler fluid needed, instead of whole new muffler?

:D:D:D:D:D

Well I don't think your muffler is causing the rough idle. It could be an injector or it could be compression. What I think you should do is a compression test. You need a compression test kit to do that. Maybe your mechanic could do it for you. But if it runs good, just a little shabby on the idle, maybe just live with it. Does the idle improve when you pull it out of gear? If it does maybe the idle speed is to low, and it can be difficult to increase as there is no adjustment screw.

I would start with an injector cut-out test. Just crack the line at each injector one at a time with the engine at idle. If you get to one that doesn't change the running of the engine when you crack the line, you've found your problem cylinder. After that, swap the injector with an adjacent cylinder to see if they problem follows the injector or stays with the same cylinder. If the problem goes with the injector, you know the injector is bad. If not, then you know it is something else.

Try adjusting the rack damper. It is easy to do and doesn't cost anything. A 12 and 14MM wrench are all you need.

If you have only just done the valves, give it a couple of 100 miles. best do a good Italian tune as well.