It could be the NTC (Negative Temperature Coefficent) AKA CTS (Coolant Temperature Sensor) on these this is located between two of the plugs, this provides the ECU with the temperature of the cylinder head metal itself on these and hence the temp of engine, it also provides info for the temperature gauge and the fans.

If it is difficult to start it could be telling the ECU a colder temp than it actually is if it has gone out of range, and so it adds more fuel so you have to rich a mixture hence the smell.

Martin