190E 2.3-16V rough idle issue
 

When the car is cold it has a rough and low (aprox. 500rpm) idle. It doesn't die or anything, but when I start driving it lacks power and if I am in a higher than normal gear under power (say 4th gear @ 35mph), the acceleration is shuddery. The colder it is outside, the longer it takes to warm up. It may be 15min of stop and go driving at abt. 53 F. before it starts behaving.

If I am under power when it warms up there as a surge of power and then my power is right where it should be. Even when the car is warm and I shut it off and then turn it back on it usually takes about a minute till the idle goes from low to where it should and my power is good under load.

Has anyone experienced anything like this? any ideas? I'm not even sure where to start trouble shooting this one.

You may want to search for threads dealing with the EHA - electro hydraulic actuator - on the fuel injection system.

For some cars a minor adjustment can make a big difference [I was going to attempt this on my 300E/M103 last weekend, but found the cover to the adjustment screw was stripped]

Sounds like a warm-up enrichment issue, especially if it runs fine when it's at operating temp. If you're running it in 4th @ 35MPH, it's no wonder it takes a while to warm up. RPM's create heat, not distance. Try downshifting so it'll warm up quicker.

As far is taking longer to warm up the colder it is outside...that's pretty much a given.

Do you have the FSM for that vehicle? Seems cheaper to buy that, learn exactly how the system works and then replace the correct part than to throw multiple parts at it on the off chance you may accidentally fix it.

Should have been more clear
 

Yes, I know it's a given that it'll take longer ot warm when it's cold and the 4th gear thing was just something I found while playing around with the car to figure out why the power was lacking.

I do think it is a fuel issue though, as when it is doing this the AFM gauge shows 5 lit bars in the middle when it's doing this and when it has proper power it stays near constant at 2 lit bars just inside of rich, when under load.

I just want to know if anyone else has seen something like this before. Thankyou for the input though and I will check out that EHS thing.

Not knowing you service records??
How long since a valve clearance check & compression check?
How old are the cap, rotor & wites?

Do you run premium fuel? 91+ octane?

Air flow position sensor is a COMMON failure that causes idle problems on 16V engines.