The engine has had a problem with a high and unstable idle speed that I have been working to track down for quite some time. I have discovered that the problem was related to how the GM ECM communicates with the OBD1 scan tool. If you work on GM cars from this era, you may encounter this issue. This video shows the problem and explains why it is happening. I have run this scan tool every time I ran the new engine and drove the car during the troubleshooting process, so that I have data to understand potential issues. The bottom line is that the tool is causing the problem due to the 10k diagnostic mode in the ECM. The fix is to stop using the tool in normal driving.


Background: This is a "Barn find" 1985 IROC-Z Z28 Camaro with Tuned Port (TPI) LB9 engine that has been parked for 25 years. The original owner passed away and his father sold the car to me. It has just over 101,000 miles with virtually no rust on the body, very unusual for spending its life in Michigan. This series starts at the beginning and runs through what it has taken to make this car run again. It will continue as I work through continuing to make the car road worthy and bring it back to its former glory.

If you like these videos, please subscribe so you can follow the ongoing work. The engine runs now, but there is much more to do.