1997 LeSabre Vacuum Leak?

[nkmhockey]

1997 Buick LeSabre Custom
133,000 Miles

I recently had the transmission rebuilt due to a full failure (transmission completely locked up and needed towed). Afterwards, there was a problem with a rough torque converter engage at approximately 30 MPH on small inclines. I took the car back to that did the re-build and he replaced the vacuum module on the front of the transmission. That helped soften up the engage, but it was still a little rough for my liking.

There are times when the TCC engages and the entire car rumbles/rattles/shakes. There are also times, usually right around 40 MPH, that the TCC will continuously cycle on and off with constant acceleration. The only way to get the problem to stop is to change where my foot is on the gas pedal (either accelerate more or less).

The above problems existed even before the transmission failed, so I suspect that they are not transmission related. While annoying, I have dealt with them since the effects are minimal during daily driving.

The new problem: consistent P0171 – Fuel System too Lean check engine light code. My fuel trim values are consistently high (long-term around +16% and short-term around +26%). The short-term trim value drops down to ~0% when the engine is revved to 2500 RPMs. The short-term trim is fine during acceleration/cruising, which leads me to believe that the problem is a vacuum leak.

I have checked all vacuum connectors and hoses, no problems. I did notice a small leak on the back of the intake manifold at the plastic connector, but that was fixed with a new O-ring. I replaced the upper intake manifold and both the upper and lower gaskets about 1 year ago. I noticed that the UIM bolts were a little below the torque specifications, so I took off the fuel rail and re-torqued all of the bolts.

The P0171 is an annoyance and has negatively impacted my fuel economy, but there were no noticeable drivability issues. Now that the temperatures have dropped in Pittsburgh, I am starting to see a new problem. When idling at a red light, in park or drive, the RPMs intermittently begin to rise and fall. The engine revs up and down from ~800 RPMs to ~1000 RPMs.

I have not seen a noticeable change in the frequency of the problem in relation to cold temperatures. However, this morning when I first started the car, the tach raced up and down from ~500 RPMs to nearly 2500 RPMs. Today was the coldest it has gotten so far this winter, temperatures were around 20F. When I checked, I had 2 new CEL codes, P0300 – Random Cylinder Misfire and P0306 – Misfire Cylinder #6.

Over the past few years, I have replaced:
Both oxygen sensors
MAP sensor
IAC valve
TPS sensor
MAF sensor
IAT sensor
Fuel filter
PCV valve
Fuel pressure regulator
Fuel pump/sending unit
Spark plugs
Spark plug wires

The plugs and wires should still be in good shape, but I will check them over the weekend. The documentation for cylinder misfires does say that the codes can be caused by a vacuum leak, which I suspect is confirmed by the consistent bad fuel-trim values and P0171.

I have sprayed around the entire manifold with carb cleaner, but I cannot find a spot that consistently causes the lean fuel trims to return to normal (0%). The only odd thing I have found is that when I spray between the alternator and the UIM, the engine nearly stalls. If I spray too much, I can actually get the engine to stall completely.

What is in that gap that could cause the engine to stall? These issues all appear to be related and have been driving me crazy over the past few months.

Thoughts? Suggestions?

Any help is greatly appreciated. Thank you.

[danielsatur]

You need consistant horse power to get the hydraulic pressure for the automatic transmission!

Plastic, rubber, gaskets, and seals go bad with Age + mileage.
Suspect EGR, or PCV system.

See how a smoke test is done, see http://www.youtube.com/watch?tv=FfiQ7qWiG-M

[imidazol97]

Originally Posted by nkmhockey

1997 Buick LeSabre Custom
133,000 Miles

What is in that gap that could cause the engine to stall? These issues all appear to be related and have been driving me crazy over the past few months.

The vacuum lines with their rubber connectors have been a problem for some people. Check the one that goes on the back of the UIM next to the brake booster hose. Those rubber pieces crack with age and rot.

In the area next to alternator you don't have any vacuum lines. I would check the UIM for cracking and check for the seal at the bottom being intact. Could the UIM be loose enough and warped at different temperatures giving varying symptoms of vacuum leaks? From reading posts by others there have been a few problems with aging UIMs leaking. Higher on the back corner is the PCV and the sensor on top of its lid. Possibly a crack in that area could be the problem.

[bigsky]

I had a bad MAF that caused surging like you described.