Cant idle below 1100rpm

[phil3r]

Hi I have a buddy who bought a 67 impala with an ls3 and tr6060 out of (supposedly Camaro SS). The car wont idle below 1100rpm even when ecu demands 550. The ecu registers as a 2011 sierra with a 6.2 I have lengthened the intake tube to have 6 inches between the filter and the MAF and that helped the idle to go down to 900rpm. Can anyone clue me in on how to lower the rpms at idle?

67 impala ls3.hpt

ive attached the tune file


Thanks in advance for for shining me in the right direction.

[Alvin]

A log would be helpful

[blindsquirrel]

Vacuum leak.

And, nothing about the Sierra's MAF table is going to be applicable now that the tubing has been altered from stock.