Is it normal to have to get into the throttle half way or more for the car to begin pulling away from a dead stop?

I just got this car on Saturday so I don't know how a normal 86 300SDL reacts to throttle input. It seems to need way too much pedal to begin moving. And even when I'm cruising along at 30 mph I'm still in the pedal close to 50%. When I get up to highway speed, it seems to take less throttle input to maintain speed. 25% of the pedal will keep me cruising at 70 mph. Might be worth mentioning that the first 30 seconds of idle on a cold start are pretty loud -- 18-wheelerish.

What I've done:
Looked at the throttle linkage for lube issues. Looks great and moves well by hand.
Checked clearance of all pads on rotors.
Replaced the first inline fuel filter and tossed in a can of Chevron's system cleaner (love their Techron on my gasser!).

Next:
I'm waiting on a delivery of the can fuel filter and the other inline filter. Also getting some D-purge in that same shipment.

My intro post: Obligatory 'Howdy" message

They tend to get sluggish with age. The '87 is exactly as you describe.........won't get out of it's own way.

What it desperately needs is an ALDA adjustment. The engine is not getting sufficient fuel at low rpm's.

There is ample posts regarding how to accomplish this on a 603. It can be done without removal of the manifold.

I've got to do the exact same thing.............it's painfully slow.

Brian, your diagnosis was DEAD ON!
3/4 of a turn ccw on the ALDA adjuster and I had a new car! Its like someone took 5 bags of cement out of the trunk. The car idles better at start, its quieter all around and goes like a bat outta hell! Its amazing. Really.

My ALDA was on pretty tight. I used some PB Blaster on the main nut and placed an 8 inch adjustable wrench on it and wedged it in between the intake manifold. The adjustable wrench handle was pointing over towards the front passenger seat. I happen to have a big antique spanner (think pipe wrench for square shapes) and it fit on the ALDA nicely. Putting a small rotation on the ALDA (and nut) I was able to put some tension on the adjustable wrench which sat perfectly while I leaned on the spanner. The dremmel made short work of the sleeve around the adjustment screw. Make sure you loosen the lock nut on the adjustment screw!! Not alot of the instrux I found mention that!

Wow, thanks again. Now go adjust YOURS!