88 Fbird 2.8L with AT would have the tachometer "spike" from idle to 1200-1500 rpm during idle in Park at any temperature (cold or normal operating temp). Also, it would "stutter" or "shudder" at idle, in gear at a stop light or any steady throttle position during driving. Engine died once while at a stop light, but immediately restarted with the spiking rpm/shudder/stutter still present.

Searched other threads and suspected the following:
1. Throttle Position Sensor (TPS) faulty or not correctly adjusted.
2. Mass Airflow (MAF) sensor faulty.
3. Vaccuum leak.

Ran codes and got 22 (low voltage at TPS -or- fuel cutoff relay circuit open or shorted to ground) and code 34 (low voltage/high vaccuum at MAF or Manifold Absolute Pressure (MAP) sensor).

Measured voltage at TPS, measured 6.12VDC.
Adjusted according to specs and condition remained, although not as severe.
2. Disconnected MAF sensor, no change or improvement.
3. Removed every vaccuum line and inspected.....
-----BINGO-----
The PCV (Positive Crankase Ventilation) valve on drivers side valve cover had several splits in the neoprene elbow that connects the vaccuum line to the PCV valve. This would explain why code 34 was flashed since the MAP sensor was sending/receiving an eroneous reading to the ECM.

Replaced the vaccuum line with new neoprene hose (3/8" diameter I think) and no more spiking rpm, stuttering or shuddering conditions.

Just sharing information that may help someone else.

 

Great info. Lots of us have this problem with our Six's along the way.