My check engine light came on rather abruptly and now the car isn't idling smoothly and there is a smell of oil/gas coming from the engine. Any ideas?

sounds like timeing to me.

have a parts store pull code, to see what sensors r at fault, tps throttle position sensor may need adjust, oxygen sensor needs replaced, may have two ? both need replaced. gas cap might b faulty ? in any event, the trouble code must b cleared out from computer, after repaired is made. if engine light comes back on, reclear it. sometimes intermittant sensor problems occur, engine light comes back on. well, the gas we buy with ethanol is killing our engines, put some fuel stabilizer in @ next fuel up. but try some fuel injector cleaner first, winter gums up injectors, soooo ! fuel filter replacement is always in need, people don\'t get it, replace all filters, air, fuel, oil, get it ? maintenance is a necessary evil. u change yur clothes ever day, right ? well, same thing., good luck, ken

Ok Run,s smooth when WArm ?Check thermostat change it or light comes on using to much fuel so replace the oil And Filter cause you have lot,s Of GAS in OIL so Replace it then Check to see if YA HAve Antifreeze in OIL see when ya Change it Ok See if ther is some If Not change thermostat ASAP ya can wreck the HEADS ON the VAN Over HEat them

I'm going to assume the smell was coming from the exhaust.
Sulfur smell is often caused by excess sulfur in gasoline or a problem with the emissions system on the car.
If the check engine light is not on, it could be the brand of gas you were burning at the time.

First off is your check engine light on? I know you said your scanner doesn't read OBD1 (pre96) but it wouldn't matter if it did if your engine light isn't on there wont be anything to read.

while it sounds like a misfire it is possible your timing is off.

To be sure, there is a trick you can do to to read the codes if the engine light is on. theres a video on youtube that gives a decent explanation of how to read it, best part is its free. Although Im not sure about the location of the code reading port on your 91, if it isn't in the normal location like the one in the video just google search OBD1 code port location (then year make and model) shouldn't be hard to find.

here's the vid: http://www.youtube.com/watch?v=V8nZpQyoRh4

does the check engine light come on or flash when the running issue starts? sounds like you have an ignition coil dropping out intermittenly.

CHECK OIL PRESSURE SHOULD BE 20 - 45 PSI @1500 RPM OR 40 - 70 PSI @1500 WHEN ENGINE RUN ROUGH OIL LIGHT COMES ON YOUR OIL LEVEL LOW OR OIL TOO CONTAMINATED.YOU NEED TO CHANGE OIL FILTER AND OIL.LOOK AT THE COLOR OF THE ENGINE OIL,LOOK MILKY COOLANT GETTING INTO OIL.SMELL OIL IF SMELL LIKE GAS FUEL INJECTORS DIRTY CAUSING FUEL TO LEAK DOWN INTAKE WHEN ENGINE OFF.

check the exhaust manifold.It is prone to cracking at the expansion joints.Causing you to smell exhaust and confusing the upstream o2 sensor

let your car idle go back to the tail pipe if it seems to be steaming alot , and or smells like antifreeze then you have a head gasket problem or a gasket leak alowing in directly into your engine

Make sure the gas cap is there and is fully tightened (it will click), a loss or missing cap will turn the check eng light on.