I've been told by the dealer that there is evidence of rust in the fuel distributor of my 91 300SE. I don't have technical expertise in this area, but my gut feel is that this engine would not be turbine smooth accelerating through red line if rust was a real problem.

In that light, what are the symptoms of a failing/failed frequency valve, overvoltage protection relay and oxygen sensor? Should I expect a noticeable change the idle or ability to idle if I disconnect these components one at a time? Again, it's velvet above 1,000 rpm.

Is there a limit on how many ways I can pester the forum with this problem?

Thanks,
Sixto
78 450SEL ... could be gone tonight :(
91 300SE

Rust is not so nice to K/KE jetronic fuel systems. Check inside the filler neck of the gas tank. Usually rust appears in that area if at all.

The 103 motors all use KE jetronic. They do not have frequency valves. The OVP relay powers the engine controller (and ABS). With it dead numerous symptoms can occur, such as: hard cold starting, hesitations, fluctuating idle, low idle etc.

The O2 sensor also can cause numerous problems and if its more than 60k since replacement it might be a good part to change without testing. Proper testing is the answer for all these things.

When I said frequency valve, I meant that idle control device that looks like a stepper motor actualted valve. I know that proper testing is the key, but is there a quick check for that idle control device?

Thanks,
Sixto

Sixto, a question like yours is no bother. In fact it is very interesting and all 103 owners will store your problem in their bank of knowledge on what to do if this problem ever comes up. Keep us posted on what happens, in detail.