Acceleration loss at random while driving

[Drewisweird]

Background:
Just rebuilt the motor, driven it around to seat the rings and get it home from school and while driving it I noticed that under acceleration it would just cut out then pick back up again almost as if i had let off the throttle then punched it again . I checked the diagnostic port and it doesn't throw any codes. Done some research and it seems that it points to a timing issue but my timing is correct, checked with a timing light and the car idles very smooth. Only other symptoms are it smells as if it is running rich but I haven't been driving it enough to see if it is in fact running rich and getting poor fuel economy.

Secondary question for anyone who knows, i know that the on board diagnostics on many older cars is lackluster at best, is the Supras any different? Due to the fact that its running rich i think i need a new O2 sensor but its not throwing a code so I'm not sure and I don't want to throw parts at it in vein hopes of fixing it.

As far as my knowledge I am quite new to this, bought the car as a project because it was cheap and I rebuilt the motor at school in shop class. Last day of school we got it to fire up and I was able to park it outside for the first time in months. Beyond the technical details of rebuilding a 7m motor I have no knowledge of diagnosing issues like this. My shop teacher says from the symptoms it could be a timing issue, air flow meter, o2 sensor, throttle sensor, or vacuum leak. I am trying to seek the knowledge of someone who is more familiar with the car so I can attempt to fix it because I am going away to college in a few weeks and I'd love to be the kid driving a Supra rather than the kid driving a Buick.

 

[Roger UK]

The diagnostics on the Mk3 Supra are pretty good . . .

If it is SUDDENLY losing all power just for a moment, then coming back on again, that can't be down to running lean or rich, that would just affect performance generally. Similarly, you can rule out the O2 Sensor, as that just fine tunes the mixture.

If the timing was out, again it just wouldn't run very well, but wouldn't cut out.

It's almost certainly an electrical fault - probably just a dirty connector on the Throttle Position Sensor.

Something people should do on ALL modern cars every 3-4 years is unplug every connector on the engine, squirt some proper Switch Cleaner/Lubricant (like Electrolube) in both sides, and plug/unplug a few times to remove the dirt/reside.

Bet that fixes your problem.

The other thing it could be is your HT Leads - again, these really need replacing on any car every 7 - 10 years, as they start breaking down (you can't test them easily, as it's just under extremely high voltage that they leak)

Finally, it COULD be your actual Throttle Position Sensor. Rather than needing replacing, again it is probably just dirty inside. This is just a Variable Resistor (or Potentiometer), like a traditional Volume control on a Radio or Amplifier - just as they go crackly due to dirt, so the TPS plays up, causing the engine to cut out. Again, it can be cleaned using Switch/Cleaner Lubricated, and the Toyota Service Manual explains how to set it properly using an Ohmeter.