Rough running / high EGT

Thank you Jeff.  I will start with checking #2 spark plug and connectors. 

Hi all

Just to clear things up a bit.  In the software of the ECU the 912iS indeed reads the EGT.  In this case it is a reporting only function and any change inside the cylinder would be reported in the data stream to the BUDS log files.  

In the case of the type 915/916 this has changed, the EGT actually will is used by the ECU to make changes in fuel flow (pulse duration) and timing as in the case of knock.  

I think Jeff is right, try moving the EGT to another cylinder to see if you have a problem with that cylinder or the probe itself.  EGT probes do fail even at low hours.

Cheers

Thank you. I will be traveling for the next 10 days and will not be able to provide results of troubleshooting until after travels. Thanks for suggestions. I will keep you posted. Drew

I have been away for a couple weeks and have finally had a chance to follow up on suggestions above. 

1. I swapped the EGT sensors for #2 and #4 cylinders. The symptom of high EGT reading did not follow the sensor. EGT temperatures continued to rise to about 1,650° in #2. 
2. I checked spark plug wires and caps for proper fitting. 

It’s strange that the temperature reading increases only at altitudes of less than 3,000 ft (sea level airport). Engine runs fine within expected EGT temperatures at higher altitudes. My main concern is whether I may be doing harm to my engine by temporarily running my engine at the elevated temperature. 

I appreciated your efforts in suggesting troubleshooting ideas. Thanks. Drew

I'm piling onto this thread with a similar but slightly different issue.  My 912 ULS underwent 5 year rubber including carbs rebuilt by Lockwood  Since then, when I reduce from cruise power for a descent, the EGT on L drops seriously - I've seen it go off scale low.  Annoying but I let it go.  THEN during a recent cruise, after about 45 min in the air at 5100 rpm, I noticed the engine run a bit rough and the EGT on the L side went high - all the way into the yellow.  Reduced power to about 4800 and EGTs returned to same as R and engine smoothed out.  Repeated the cycle with same results and turned for home.  Once turned around, the engine ran rough and the EGT went into the red.  Tried brief burst of higher power and then lower power and headed for nearest.  After about a minute, at 5100 rpm, engine smoothed out and ran fine.  EGTs remained normal until I reduced power to land.  Then I got the precipitous drop on the L but I don't notice any obvious rough running.  Plugs look fine - running high octane mogas.  

Help.