I have a S4 TII with a 1987 TII ECU. The car runs fine when it first starts, but after reving once, my VREF voltage and all the associated sensor drop by .1v and it runs like crap. Why would the output voltage drop.

 

if you don't touch the throttle does this still happen?

are you measuring VREF off the TPS?

MAP Sensor will have a VREF as well... only those two places I can think of on a toyota engine, not sure about 13b.

 

If I fire up the engine and let it idle, the VREF at the ECU connector reads 4.96v. After I rev it once, the voltage at the same connector drops to 4.85v. My signal from the TPS in turn drops from 1v at startup idle to .85v at idle after reving once.

 

Check the condition of all your grounds, especially the ECU ground.

Also, is the plug at the back of the alternator plugged in and wired correctly?

 

Personaly I wouldn't worry about the ref voltage. I think the TPS voltage drop is a result of the throttle movement more than anything.

Remember, when you set the TPS to an output of one volt, the engine needs to be fully warm/hot due to the thermowax/fast idle cam/etc.