I am curious to find out what your exact idle problem was, and what model it pertained to. Most of those that have chimed in to my post with similar problems may or may not have what I am describing as a problem, so I'll go over it again and see if we are similar in symptoms.
Initially when I start the car cold it runs fine with near perfect idle. After the engine has warmed to operating temps, let's say 3-5 miles and the car is brought to a stop for say a minute or so in drive it goes into this bumping/missing action which lowers the rpm to around 500-550 rpm. At the same time it's acting up in most cases, the temp gauge starts to increase slightly, on a warm day of 85-90 it increases to about 110C if in traffic. When you start to accelerate it continues to miss until you can achieve an rpm of about 2000 at which point it smooths out like nothing is wrong at all and power is restored. Reading post on several sites this problem seems to be common, but not saying that the actual culprit causing the problem is the same as several think it is fuel related, others lean toward air intake and still others find it to be an electrical problem from a simple cap,wire and rotor replacement to everything electrical under the hood that is hooked to the ecu. I will tell you that there are an awfully lot of parts to cover if this is the case to isolate this problem. It would be hard to understand that an electrical system such as wires, cap, coil and plugs that perform great at high engine speeds die when it comes down to idling at 600rpm's verses 3000rpm. I am almost convinced seeing as engine temp goes up at an idle and that's where the problem escalates, that a bad coolant temp sensor could be a problem if it sends it's input to the ECU for adjustment. The hotter the engine seems to get, the rougher the idle tends to get as well.
If you have light to shine upon this problem that I am just not seeing, and trust me, there's a lot of dark area here. Give us your knowledge. I am open to all suggestions that don't open my checkbook up as well with replacement parts that didn't make the difference.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan