[motomick76]

UGH, MAP sensors. Guys over at TM forums actually bench test the sensors with air compressor. Put a regulator on, and carefully test the full range of the MAP.

 

[motomick76]

Remember with my van, the MAP issue would not appear until long periods under load, then it would start to fail, go from 3.5 volts straight to zero. I found it when I ran two wires from under the hood into the interior, and hooked up my mm, and watched the voltage. I pulled the rubber grommets back from MAP connector, and just shoved the wire down the connector - one for output voltage, and one to ground. When it would get around 4500 rpm, the voltage would go from 3.5, to zero, then jump back up and down. Then then motor would not rev, as in the video.

If that does not work, try the input voltage to MAP, make sure it does not drop off or fail.

 

[motomick76]

So here's what I've tried. I eliminated all manifold vacuum except MAP/BAR, brake booster, FPR, and PCV. (It's pretty hard to disconnect the PCV, but I also swapped out the grommet and even tried zip-tying every joint.) The wastegate solenoid was also still connected. Behavior was about the same, and the buck/surge problem was still present.

I bought a $15 TPS on eBay. It was 0.75v at closed throttle, 3.96v at WOT. However, the computer immediately (and consistently) gave code 24, "Sensor output less than 0.16V or greater than 4.7V". Reinstalling any of the used sensors cleared the code. I then bought a $36 TPS from CarQuest. It did the same thing.

I soldered a new ground from the TPS harness to the throttle body and also to the battery negative. No change.

I replaced the MAP/BAR with a set from another 16v Spirit, and it refused to run. It would sputter and cough, no codes. I put the original pair of sensors back, and it worked "normally".

I'm out of things to try. I'm not doing anything exotic. I'm just trying to get it running STOCK!

Measured voltage, is that static; vehicle in park? I would suggest monitor TPS and MAP voltage when it bucks/surges. Run wires into the interior and observe with MM both TPS and MAP. Only way to nail this down is to start observing voltages during the issue. If it surges, then voltage drops, it is not the issue. If voltage drops, then it buck/surges, it is your issue. Process of elimination.

 

[motomick76]