hello all!

i'm new to the forum, but the answers i've read seem excellent. here's my situation:

i recently bought a '79 300TD wagon on EBAY. see here:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2483568331&rd=1&sspagename=STRK%3AMEWA%3AIT

it's in chicago and i'm in cleveland, so naturally i went there to get it. i picked it up no problem, it started no problem, and drove off the lot no problem. THEN, about 15 miles later, the car would not stop revving up. i've come to learn that this was because i had turned the unmarked knob on the dashboard all the way up, the one that apparently operates the throttle. then, after another 10 miles i lost all power in the brakes and was forced to do an emergency stop with E-brake and turning the car off.

here's the explanation i was given:

the knob was turned up, got stuck there, and while the car was unable to slow down it's RPM's i lost vacuum pressure and thus the brake booster.

here are my questions for you:

1. can i manually unstick this knob, or do i have to have the part? i can make it back home slowly, i.e. turn the knob down and replace it when i get home, if that's possible.

2. the car had problems with pick up, then it had problems with not accelerating, then it wouldn't stop accelerating in neutral or park, but would have no pick-up in drive. it would hold speed well, though. also, it had a slow response when i first drove it, before fiddling with the knob. why?

3. is that brakes explanation accurate, or is there a problem with the vacuum system?

4. what is the proper way to utilize this knob?

5. are there any other cronic mercedes problems i should be on the lookout for?

please keep in mind that i know what i'm doing around gasoline engines and cars, i'm just new to diesel. i'm very skilled mechanically. i've never owned a diesel before, and i didn't think i'd need to adjust that much.

also, the car is imaculate other than this problem. the suspension is gorgeous, it came from a rich suburb of chicago, and it was donated to the salvation army, which leads me to believe that someone's wealthy grandmother needed a new car and preferred the tax write off to the hassle of selling it for $1525.

the urgency comes with the fact that if i'm going ot go and pick it up again, i have to do it on monday, and i need to notify this guy of my decision by saturday.

please respond with any and all help, i'll really appreciate it.

nick