Saturn 2002, SC1- P0172 & rough idle

Question

Rough idle and Engine light coming on and sometimes going off for a while.

PCV valve and hose appear in good condition and I ensured it doesn't leak.

I also sprayed some Brake Cleaner all around the intake twice today and did not get any response from the engine. I may have to try it with Carb cleaner as the spray was more direct than an actual spray.

I did some Live data scanning today with my meter and would like to tell you the results to see if it indicates or supports a vacuum leak or anything else.

After car was warmed up, no Engine Light on, I hooked up the scanner.
1. Engine idling around 769Rpm
2. Engine Ignition timing Advance Cyl#1- 11 Degrees Advance (+)
3. Closed Loop Control using Oxygen Sensor - Normal
4. Intake Manifold Pressure 53kPaA or 7.7PsiA
5. SHORT TERM FUEL TRIM: approx 33.59-36%, Lean(-) (I assume that means -33.59%).
6. Long Term Trim 0% (Was setting at idle)
7. Coolant Temp: 64 Deg C, 147.2 Deg F
8. Intake Air Temp: +4 Deg C, 39,2 Deg F (***this was odd bec it was -12 Deg C outside at the time).
9. O2 Sensor 1 approx 0.935 V when Short term fuel trim at 19.53% Lean(-)
10. O2 Sensor 2 was approx 0.855V

After I started to drive the Long Term Fuel Trim started to go up then settled down at 0.78% Lean(-) and the Short Term FT: 0% and not fluctuating at all. I checked the Fuel Sys Status and it showed as in "Open Loop Control due to System Fault". When I let up on the gas the Long Term FT switched to 4.69% Lean(-), then as soon as I pushed the gas back to 0.78% and back and fourth. I then reset the system.

Note: As I was driving the Intake Air Temp sensor slowly dropped to -8 Deg C but that took 40 min and as I stated it was -12 Deg C outside.

Note: The car never warms up past 1/4. Is this normal? Could this indicate a bad Thermostat?

So after I reset the system I kept driving and it went back into Closed Loop using O2 sensors. The Short term FT started fluctuating again anywhere from 5%- 50% Lean(-) and the Long Term FT fluctuated between 15% - 21% Lean(-) and seemed to stay around 21.88% Lean(-). The only way to get the Short Term FT to show in the plus was to push the gas peddle significantly and hold it. then and only then would the short term FT go in the positive: Rich(+).

As I was driving I had to come to a stop due to traffic and within min the engine Light came on and I drove the rest of the way to my destination.

Once Parked I let the car idle and looked at the final readings:
1. Coolant Temp: 74DegC, 165.2 Deg F
2. Intake Air Temp: -4DegC, 24.8 Deg F
3. O2 Sensor 1: 0.590V, Short Term FT was 50% Lean(-)
4. O2 Sensor 2: 0.215V
5. Fuel Sys was still in Closed Loop Control
6. Ignition Timing Advance Cyl#1 showed as 15 Deg Advance(+)
7. Intake Manifold Pressure 46-50kPaA or 7.3 PsiA

DTC: P0132- O2 Sensor High Voltage Bank1 Sensor 1

I drove home later in the day and put the scanner on again to get the Freeze Frame and the only code that was showing then was P0172- Fuel Trim too Rich. Attached is the Freeze Frame picture for when this code was detected.

Note: Several months ago I noticed that one of the bolts on the EGR valve was stripped so I used a sealant when I put it back on. The second bolt went tight so I did not think it too much of an issue and with the sealant I do not think that it is leaking, as it would be noticeable bec of the noise.

Note: There are no exhaust leaks.

Note: Sometimes at idle the fumes coming from the car exhaust smell very bad.

I don't think it is the fuel regulator bec I put a new fuel regulator on the car last year. Could I possibly have a bad fuel pump?

The DTC seems to come mostly when the car goes into idle. It does idle VERY rough.

Let me know if there are any specific tests that I can do to pinpoint the problem.

Could the non-accurate reading from the air intake temp sensor cause this?

I appreciate any help.

Read more: http://forums.automotive.com/70/9533024/engine/rough-idle-and-p0172-code/#ixzz2psJ3bHHQ

Answer 1

Intake manifold pressure or the MAP sensor is too low, A short term that is 33% , you can get this if you disconnect a PCV line, The short wil climb to 33%. . As your evalutation you ensured there is no vacuum leak, This engine is a speed density engine, which uses a MAP sensor . The engine mangament is adding fuel to balance the fuel trim. What can cause a low MAP are back pressure from a plugged catalytic.  The intake air temperature sensor correction are so small it affects nothing, It takes the ECM to report a bad intake air temperature sensor. The next situation that can cause low MAP reading is fuel pressure, Low fuel pressure will cause the long trim to increase above 10 % and you would code up a lean condition. A low MAP with a rich running condition this is a mechanical problem