2006 Acura TSX engine hesitation between 2-3000 rpm

Hi everyone, I have an Acura 2006 tsx and recently it showed the DTC code of p0137, I changed the o2 sensor downstream. After a few hours still the same issue. I noticed the STFT was always rich. when it would reach -25 or more it would start to hesitate and almost want to shut off..even after I press the gas pedal it will not accelerate. I searched and found that the MAP sensor may be the issue. I downloaded the service manual and it said it should be reading 160 or more kPa ..mine was reading only 99 when key switch is on. When I unplugged the MAP sensor, the sensor was reading 177 kPa at all times. The voltage on the connector was reading 5v reference, ground was strong. I haven't yet back probed the MAP sensor to test the signal wire but Im pretty sure its strong because its intermittent failure..so the engine hesitation would happen randomly . When I drove the car with the MAP unplugged it would be very good and no issues...the O2 I have is a reversed reference so rich is low voltage and lean is high voltage. When I drove the car with MAP unplugged the O2 was always between 0.5-0.9.

Can I be safe to say I have a bad MAP sensor? or is it possibly something else?

The different units for measuring engine manifold pressure do my brain in :blush: :blush: :blink:
reading The first sanity test for MAP sensors is to look for a somewhere about ambient air pressure at Key On Engine Off. At sea level in average weather ambient air pressure is around 101 kilo Pascal --- as most of us live above sea level expect a lower pressure more so in stormy weather so a reading of 99 kilo Pascal is about normal Key on Engine Off.

Key On Engine Running at idle I would expect to see 60 to 70 kilo Pascal, turning engine loads such as the head lights, heater blower blower, wipers on should cause this to go slightly higher as the IAC compensates by letting more air into the manifold to maintain idle speed.

When you open the throttle the pressure in the manifold should increase (more kilo Pascals) and go down to a lower pressure (higher vacuum) when the throttle is snapped shut.

Thank you for that info ..during idle the MAP reads max of between 20-35 kpa ..in the service manual it said that if it doesn’t read 160 or more with key on then it’s an intermittent failure .

20-35 kpa translates to around 7 in hg. Subtract that from your local barometric pressure, which is probably around 28 in hg, and you get 21 in hg. That's a reasonable reading, and indicates a mechanically healthy engine. The reading of 99 kpa KOEO is also reasonable. Unless you're looking at an intermittent issue, I doubt you have a bad MAP.

I think you're creating a false result by unplugging the MAP by putting the car into open loop. In that state, the PCM will command a generally rich condition, and thus the symptom goes away. You could confirm the open loop by unplugging the MAP and checking the Loop state on your scanner.

IMO, the negative fuel trims combined with the hesitation strongly suggest a false rich condition, which calls the upstream air/fuel sensor into question. I also think the P0137 is likely a symptom of the false lean, not the cause. Something causes the PCM to take all the fuel away, and the downstream sensor goes dead lean long enough to trip the code.

I think your next easiest test is to get the trim pegged rich again, and compare the reading of the upstream sensor to the downstream. If the upstream sensor is pegged rich, but the downstream is pegged lean, then it's likely the upstream sensor is lying. Use the upstream sensor current PID - positive current is rich, negative is lean. Here's some known good data from another Honda 2.4L for reference:

www.scanshare.io/share/ZsdIdUM6zkK47APTf-fFqw#0,2,3,5,32,42,43

Thank you for the reply ! ...the issue that I have with the car is indeed intermittent ...sometimes as soon as I start the car and drive it hesitates hard and almost stall...other times no, I can drive it for couple of days untill randomly on the high way or at a stop it start to jerk hard even as I try to raise the RPM it wont accelerate ..till I shift down with manually then the rpm would spike and start to accelerate again.

On a side note, today I noticed ..I had the STFT and MAP sensor graph on my OBD...when it was pegged -31 ...the kPa was shooting between 30-91-64-97 kPa then once it stabilized the car start moving normal.

Yeah, intermittent are usually the worst. :silly:

In the past, I've had luck catching bad air/fuel ratio sensors by jamming the mixture very rich and very lean at idle. Usually by pulling the brake booster hose off, then adding brake/carb cleaner to the same hose.

Same rationality as using the downstream O2 sensor. If you're dumping fuel in but the sensor indicates lean, the sensor is wrong. Or, if you stop adding fuel but the sensor sticks rich afterwards.