gwest1984

I'm also experiencing this same issue running an A-tune in my '89 951S. I've now taken my intake manifold off three times now to confirm no vac leaks. Starting to feel stumped.

Rogue_Ant

If the hesitation is at 0-5psi, then check that your MAP sensor is properly working...

With the ignition on, but engine off, measure the voltage on MAP sensor's green wire (do not unplug the MAP sensor). It should read ~1.5 - 1.6 volts.

Now start and let the car idle, and measure the voltage again. This time it should read ~0.6 - 0.7 volts.

If it is reading zero, or close to zero volts, most likely the MAP sensor's green and black wires are incorrectly wired...

Here is the proper wiring:

Emily750

I have the same problem. I'm going to check the map sensor.

bw993

At idle (cold), my MAP measures a little high ~1.01 volts, not 0.7 volts.

Rogue_Ant

How much vacuum are you pulling?

bw993

At cold startup my vacuum is 12, at warm idle it's 16-17. I measured 1 volt at the MAP on cold startup.

Rogue_Ant

Your reading is normal.
~1volt is roughly 11" of vacuum (at sea level).

bw993

Thanks.