Surging and rough idle

I have a 92' 325i that I replaced the head and put all new intake gaskets. And vacuum lines.



But I have been chasing a rough surging idle.



I put a vacuum gauge on it when it was warmed up and I got right around 12-14" which seems a bit low but I have 0 vacuum leaks. I even smoke tested the intake.



Today I put a scan tool on it. I had the obd1 connector. To my surprise I could actually read live data. Coolant temp was spot on with intake air so I know those are good. The only one that was out of the ordinary was rpm.



From what the scan tool was showing it would fluctuate between 0-500 rpm at idle but it stayed mostly at 0-20.



But my rpm gauge itself reads fine.



I have no cell on the dash but on the scan tool I was getting a code 16 which on the scan tool said crank pulse generator.



What are your thoughts?



Could it all be due to my cam to cam timing. I did not use the can hold down tool when doing can timing.



If it helps it is a non vanos 92. It is actually a 5/92.



Thanks



Curtis

Surging and rough idle