I faced this problem with a 300SE 1988 also but it was really so so so hard to discover. It was a little clip on the side of the ignition steel box (I don't know it's name). It works like the spring. The problem was this clip is opening without closing. (Sorry I can't explain it in good English). I'm searching for a picture for it but couldn't fine sorry. It's small size to control and connect the pedal arms.

I'm using non-technical words because I don't know the real names of them!

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Master Computer Engineer, A+, Network+, MCP/MCSA/MCSE 4/2k/2k3 - Messaging, MCTS, MCITP, MCT, Brainbench, ICDL and starting Ph.D

380SE 1984 <------- Totaled by flipping accident
300SE 1988 <------- Sold
Volvo S70 2000 <---- 4 family
Opel Omega 2002 <-- 4 family
560SEC 1989 <------ Sold
560SEL 1990 <------ Sold
560SEL 1991 <------ 4 my mother
560SEL 1989 <------ Sold
600SEL 1992 <------ Current

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