a little help on codes
 

i have a 91 rxt2 and im having a little problem with the check engine light. my problem is whin i first crank up she runs great no problem.but after a while of running the check engine light comes on and it spits ,stumbles,sputters.etc. i shut it off , crank it back off and its fine for a while. it has no pattern as of yet that i can see. it comes and goes. whin i shut it off the engine light goes off and clears,ive tried to run code on it but it just wont hold in the ecu. please a little help thanks.

bump for a little help

Your car is an S5 and it's easy to check the CEL codes.
1) Ground the initial set connector (green, one pin connector next to the battery, drivers side)
2) Turn the key to the on position
3) Watch the CEL light. It will generate a series of flashes (long and short ones) The long ones are tens; the short ones are ones. So, if you see a long one followed by three short ones, the code is 13.
4) If more than one CEL code has been stored, the CEL will pause for a second or two and go on to the next series.
5) The CEL codes and what they mean can be found in the FSM in the Fuel Section. Once you know the codes you can then start working on a fix.

i have allready done that.but nothing shows whin the car isnt running. it only goes stupid whin the car is running.whin u shut it off ,and crank it back up its fine for a while.the ecu isnt holding the code. any idea what would cause this to happen?

I'm having the same exact problem. I haven't tried checking codes though... yet.
Bump, for some opinions.

Oil Metering Pump, That 's your problem I can almost guarantee. I had the same prob with a '90 NA , Car starts fine runs for somewhere around ten minutes give or take, engine light flickers and comes on, turn off the car process repeats.

When the electronic oil metering pump fails the ECU goes into limp mode (bogs, falls on it's face)

I have a good working one if you want to PM me.

thanks for the input i do have another omp to try,but the thing is im running premix.the omp doesnt have any lines on it blocked off and the wires are still pluged in. do you think that plugging the omp could have hurt it?

you were right hasnt done it since i changed it thanks for the input thanks again

I had this exact same problem a couple of weeks ago...pull your ECU from under the carpet on the passenger side of the car. You will need to take the covers off the ECU and check for any water damage and/or burnt traces on the boards or even burnt diodes/transistors. I have a vert and my ECU was soo water damaged from previous owners leaving the top down in the rain, that most of the pieces on the boards were corroded together.