The rotten egg smell is from either a rotten egg
, someone left hidden in the car, or more likely a bad catalytic converter.
Catalytic Converters can be ruined from various fuel additives used in the past, and/or from too rich of a fuel mixture (causing the CC to run very hot). A rich fuel mixture can also be commonly from a leaking Fuel Pressure Regulator. This condition can be hard on the 02 sensors that may also not be working correctly.
To access the FPR you will need to remove the intake cover.
Never start a 93-94 Northstar with the top of the intake removed!
With the top of the intake removed you have no throttle control. The engine will run wide open and may rapidly destroy itself or cause serious engine damage. The top of the 93-94 intake manifold is not a decorative piece to just take off, as in later models. It is the "cap" of the intake plenum. Removing and replacing the top unnecessarily will start to compromise the gasket of the Fuel Rail and will lead to poor sealing, idle and drivability problems.
The oily residue in the bottom of the intake is normal and it is not necessary to sop it up; it will just come back. It is from crankcase and gas vapors settling out.
The Torx screws on the 93-93 intakes are special; in a strong backfire it will allow the intake cover to lift slightly against the rubber isolator pieces on the screws, to relieve pressure, rather than burst the intake manifold. If you lose one replace it with the correct screw and isolator combination from the dealer.
Unless you are really inspecting for a fuel injector or FPR problem, you should not remove the 93-94 intake cover.
To check the FPR:
Unplug the (4) coil wire plugs at both ends of the coil pack for safety. If the engine starts with the cover off it will runaway; due to uncontrolled air intake.
Pull off the front spark plug boots.
Lift the plastic sparkplug wire carrier from the intake and shift out of the way.
Remove the magnesium intake cover (all of the Torx screws, not the 4 hex head screws). Turn the key to the ON position and look for seepage from the nipple, on top of the FPR. Any fuel coming out of the FPR nipple, and it needs to be replaced.
To replace the FPR you will need to lift the fuel rail out of the way. Exercise care or the fuel rail will break.
Replace plastic sparkplug wire carrier, and plug the spark plug boots back in.
After replacing the intake cover be sure to plug the (4) coil wire harness plugs back in.
To check the 02 sensors:
Start the engine and allow to completely warm up.
Enter the diagnostics mode and review the DATA for the 02 sensors. The voltage readout should vary from 0-1.16 volts. The value should vary frequently; a slow or not changing value means that the sensor is not working correctly.
PD32 Front 02 sensor
PD33 Rear 02 sensor
Front sensor is easy to replace, rear is hard.