jph46

Hi guys.....been helping a friend his 91 L98, NOX reading really high at smog check. Replaced the EGR valve, checked for any blockage in the. Intake, and replaced the EGR solenoid. Question is: at idle is there any measure of vacuum at the throttle body fitting on the bottom of TB? Does the vacuum depend on the RPM of the motor?
Thanks

65Z01

I've seen that manifold vac. will vary some with engine RPM.

Does it go into closed loop, is the mixture rich, lean or normal?? Diagnostic mode will show these parameters.

jph46

Will check it early next week, let you know what I find. Thanks