300e "stumbles" when hot, O2 sensor?

Hello,
My 300e ('89, 130,000 miles) runs fine when the engine is cool during cool weather but during warm weather when I come to a stop after running
continuously on the highway the engine will miss on several or all cylinders at idle but not die. Usually this will stop after I drive moderately around town but it still happens occasionally on a hot day when I'm in town. I have also seen this happen after being parked at an idle for about 20 minutes with the ac on and the problem got progressively worse until the engine almost died.
I have replaced the fuel filter, fuel pump (one of two), fuel injectors, spark plugs and wires, distributor cap and rotor within the last six months so I assume these aren't part of the problem. I have a new coil on the way but somehow doubt that that's going to help much.
My mechanic thinks it's the oxygen sensor (hasn't tested it but says he can) and has suggested I first try a bottle of fuel additive in a tank of gas to see if that helps. I did just have the valve stem oil seals replaced because the plugs were fouling in 3 or 4 months. Could the O2 sensor have been affected in the same way as the spark plugs and be causing this problem?
Many thanks,
Mike
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
O2 sensor? Why not, almost everything else is new.
If the O2 sensor doesn't fix it I suggest you think about a bad engine temperature sensor that no longer "tells" the computer that the engine is very hot and needs, perhaps a bit faster idle or a bit leaner air / fuel ratio.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks TG. I'll have the new sensor tomorrow but darned if I can see where it's located and the cd manual I have is of no use. Any clues to where it's located?
Thanks,
Mike

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I did replace the O2 sensor and that has fixed the stumbling problem but I also had just replaced my plugs (because of the oil fouling) with planinium instead of copper. The incorrect plugs made the engine feel like it was running on 5 cylinders at best.
It's all good now and I'm just waiting for the next problem to rear its ugly head.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.