This is from RKRIEG3 -

I need some help figuring out what'* wrong with my bonnie. The check engine light came on tonight while driving on the freeway. Scanned the computer and found code p1371."electric spark timing signal not switching after enable." A search on Google found a bunch of stuff for the LS1 opti. The only thing bonnie specific was DI low resolution circuit. Symptoms are intermittent sudden rpm drop and engine almost dying while driving freeway speeds. Anyone dealt with this before? Is it fuel, solenoid, sensor? Please help. Thanks in advance.

The Optical timing signal is not reaching the PCM after enable. This can be due to water in the cable or oil on the optical reader.

The 4X reference pulse comes from the opti, so if the trouble code is coming up, it may mean either the opti isn't generating the pulse reliably for some reason, or the wiring to the PCM is faulty.

It is a common problem for optis to get oil in them when the rear seal starts leaking. If oil gets on the optical wheel, it might interfere with its ability to generate either the 360X or the 4X signal.

Clear the DTC and if the code comes back, them you need to look at the opti or the PCM.