Robert,

Don't know the answer but am sure interested if you solve it. Have been a fellow suffering for 2+ years and although I've tried various remedies it's still not fixed. The symptoms you describe are so close to mine I already feel a bond between us . In particular the problems being only seen in that period post cold start but before fully warmed up, and most significantly, that 2+ days of inactivity cause the problem to be more acute, and never any trouble codes.

A couple of things to note though: (1) our cars are not quite identical – mine is ’92 but has the 104 engine which uses the KE-Jetronic injection system (CIS-E/EZL). (2) my problems are slightly milder than yours with a rough (hiccupy) idle being the norm, with an escalation to complete stall/20 min wait only occurring every 6 month or so.

Think I've read all the warm engine misfire/hesitation/stall posts on all the main MBZ forums, and have tried most of the proposed solutions - thus I have new plugs, leads, dizzy cap, crankshaft position sensor, OVP relay, fuel filter and air filter. I've also checked for air leaks, cleaned out the Throttle Body and Idle Control Valve (ICV), tested both the O2 and engine temp sensors and tried injection cleaner fuel additive.

There are more things on the list of people’s suggestions to try such as replacing the: coil, EHA, injectors, ICV, CIS-E, EZL, MAS, etc. but have been holding back mainly due to the expense. The thing that seems particular to me (now hopefully us) is the seemingly intermittent nature of the problem (car can run fine for several weeks) but that 2+ days of non-use consistently exacerbates the problem. My understanding is that these subtleties in our symptoms should let us rule out most of the proposed remedies.

Just recently in a post I received from a UK forum someone pointed me towards the charcoal canister that forms part of the EVAP system which was a completely new area to me. Reading up about this has lead me to look at the switchover valve and purge valve in the system – the interesting thing about them being that they only come into play when the engine warms up, intermittently cause air (fuel vapour) to be added at the intake manifold, and they are controlled by a vacuum (that I presume could dissipate over time – e.g. 2+ days!).

Not sure if I’m putting 2 + 2 together and getting 5, but on reading “trants4md”’s post to you I did start to get excited – not that I’ve a warm-up regulator either, but could I/we be suffering from a minor vacuum leak internal to one of the valves?

Going to have a good look tonight then the car will be left unused for 4 days over Easter. Will keep you posted if I find anything….

Regards,
Neil
Car: '92 300 CE-24 (LHD) cabrio