Hello Yotatech patrons!

I have finished my first rebuild (ever) of a 1991 3VZE and I am having a hard time getting it to run properly. It idles beautifully, but when I give it throttle, while in neutral, it revs up fine and when I release the throttle the idle RPMs drop to probably around 100 RPM and then bounce up to around 800 RPM and then back down and so on. Often times it will die, but sometimes it recovers back to its normal idle speed after about 30 seconds of fluctuation.

I have replaced the TPS, MAF Sensor, fuel filter, all wires, spark plugs, distributor and cap. I have cleaned the EGR valve and tracked down any vacuum leaks that I could think of. I have adjusted the idle speed and timing to all manner of degrees BTDC. It seems like the best was at around 25-30 degrees BTDC, but I know that is well out of the range so I brought it back to around 12-15.

Help me YOTATECH Gurus...you are my only hope...other than towing it to a shop, but damn I do not want to do that!

Thanks

 

I'm on my third 3VZ now, I feel like I've had every issue under the sun with em at this point. First thing, did you adjust the TPS when you installed it? If you remove it or rotate it you have to sort of reclock it so it's tightened down in the right position, the FSM has a guide on how to do it. You need a set of feeler gauges and a multimeter. after that give the AFM a shot, there's a few voltage tests to run to make sure it's functioning properly. You said you replaced the MAF, these trucks have an AFM(airflow Meter) that essentially serves the same role, but if it's a new one it could be a low quality aftermarket rebuild or if it's a used one, just a bad one. I also had a bad injector cause some odd running issues once but it wasn't exactly what you're describing. My money would be on the TPS being out of adjustment. Did you have the truck running before the rebuild?

 

LOL! Slow down! A Mass Air Flow sensor (MAF) and a Volume Air Flow sensor (VAF) are both airflow meters, but they use fundamentally different technology. (a mass air flow sensor measures mass, and a volume air flow sensor .... well, you get it.) If you just don't know (or don't care), call it an AFM. But if you want to understand how your Toyota really works, called it a VAF (it's not a MAF) and know why.

When you set timing, did you select base timing by jumpering TE1 to E1 in the diagnostic connector? Do you have the underhood sticker, which gives the correct base timing?