1 - I've started the thing probably 30 or so times since owning it. It has started perfectly all but 3 of those times. On those 3 occasions when I have turned the ignition key the engine will turn over but the car will not start. After a couple of seconds I have disengaged the key and tried again with it starting immediately. What does this sound like a symptom of? Is this a common issue, and if so, what is the diagnosis?
2 - I have some very small areas of rust (the main spot is on the hood along the edge closest to the steering wheel (right up by the windshield wiper blades). What is the best way to take care of this issue? Is it best to sand it down and then primer and paint over it? Or, given its a small area and not extremely noticeable, am I better to leave it as is for now?
3 - At idle, the hood seems to shake. Not bad and it's probably nothing, but should I be at all concerned? Does this mean it is idling too rough or anything, or is it pretty normal?
1. Starting; since the starter turns the engine over, then the battery would seem to be OK, and the problem is actually starting the engine. You have not reported that you have any problems with the engine running (and stopping randomly) so it doesn't seem that you have a fuel pump problem (or associated K40 relay). The fuel enrichment is done by scheduling (ie plan) rather than misleading the controller (air leak paths decreasing air, so increasing relative fuel). So the lack of start is an absolute "lack" of fuel or spark. I wonder if the starter controller is a different controller to the ECU?
2. Rust; the bane of older vehicles. But somehow the SLK seems to be quite robust, excluding the edges of the wheel-arches, so it is a minor inconvenience. I used a paint that is also seals against rust (HammerRite/SmoothRite) for the inconvenient blisters that show and annoy, rather than prime, mid-panel scratches. And, as mentioned above, once funds and need come together, I will get the rust issues dealt with properly.
3. Hood shaking: Three parts to the problem;
3a. Is the engine bucking about with a bad tick-over? Check that with the bonnet open.
3b. Is the whole car bucking about, even if the engine is not moving too much? Then the engine mounts need changing.
3c. If only the bonnet is moving, then chances are some of the supports for the bonnet are not in place, so the bonnet is "rattling". Try pushing the corners of the bonnet down, and see if they move; if the front ones do, then the latch and two corner rubbers need to be set up to establish the shut-line.