My 2004 3.6L (1SC) has random vibration (lumps) during idle, worse during cold start. VIN# ... 40112860. Dealer CND my first complaint at 3K miles. I test drove a new 3.6L 1SC CTS at another dealer, no lumps, no vibration at idle. Took it back in at 7K miles with same complaint. Tech acknowledged the problem and supposedly "reprogrammed PCM". Car still idles rough, randomly vibrates noticeably. What do you suggest as a next step?
The 3.6L does not have an IAC valve. It controls air via the electronic throttle. There should be a service bulletin on rough idle. There was a calibration change after start of production to address this issue.