Abstract: A pipe (40) having a specific length is filled with nitrogen gas (4a). From opening ends of connecting portions (42, 42) located at respective ends of the pipe (40), cross sectionally hat-shaped block plugs (50) made of brazing material are pressed into the connecting portions (42, 42) respectively and are fitted thereto for the purpose of sealing the pipe (40). Next, one end of a connecting piece (60) is inserted into the connecting portion (42) of one pipe (40) so as to break through the block plug (50) fitted thereto. The other end of the connecting piece (60) is also inserted into the connecting portion (42) of another pipe (40) so as to break through the block plug (50) fitted thereto. Thereafter, the block plugs (50) are melt so that the connecting portions (42) of both the pipes (40) are brazed with the connecting piece (60).

Abstract: According to the device of the invention, measured values (V.sub.0 ', V') of an output V.sub.A of an opening sensor at two adjusted levels of throttle openings in both idling state and fast idling state and their ideal values (V.sub.0, V) are used. The value V.sub.0 ' in the idling state is subtracted from the output V.sub.A in a driving condition, (V.sub.A -V.sub.0 '), which is then multiplied by the ratio of ideal variation characteristics of the sensor output for a change of the throttle opening to those in the throttle valve product used, {(V-V.sub.0)/(V'-V.sub.0 ')}, to produce a correction signal T.sub.A matching the individual difference. Further, a reference value subtracted from the output V.sub.A in a driving condition is set as T.sub.AMIN which varies with the output V.sub.A, taking the difference of variation characteristics of the sensor output from ideal characteristics into account.