Thread: Intermitent idle and cruising issues

1995 grand prix se 3100 sfi V6: 182,000 miles

Problems:
-Idle is irregular, flutters between 800-1000 rpm, but doesn’t stall
-Car slips (or surges or whatever) when holding a constant speed but only when the speed is above 45mph
-Car runs like a top when you are just driving around town and keeping the speed below 40mph

Items that have been replaced:
-Battery
-Alternator
-Air Filter
-Oil Filter
-Oil
-Spark Plugs
-Wires
-Cam Shaft Position Sensor
-Throttle Position Sensor
-Map Sensor
-Blown Fuel Injector Fuse
-Brake Pads
-Rotors


-Cleaned Throttle body, IAC, and pathway (in the upper intake plenum) leading to EGR, as well as the EGR itself.


Ideas of what the problem is:
Most likely:
-Oxygen Sensors
-Fuel Filter
-Fuel Injector
-Vacuum Leak
-Crank Shaft Position Sensor

Least likely:
-EGR
-IAC
-Ignition Coils
-ECM

Any suggestions on where to start troubleshooting?

Have you scanned the car? My upstream O2 crapped out but even disconnected it will read a steady 450. I would scan your car with a scanner that has live data and see whats up.

I tried testing it for vacuum leaks today and had no luck.

However, I drove it around some more today to get a better feel for the problem and realized that the "slipping" only occurs when the car is in 4th gear.

After a little reading, the idea got in my head that there might be a problem with the torque converter. (specifically the clutch?)

- "The fault is due to the lock-up clutch within the torque-converter. The clutch is normally only locked (engaged) when cruising in 4th and 5th gear. It is used to reduce losses in the torque-converter, without the lock-up clutch, the pump and turbine 'slip' in respect to each other when cruising, this reduces fuel-economy. When the lock-up clutch engages it mechanically locks the pump and turbine so no energy is wasted...

Blah, Blah, Blah

The shudder also goes away when heavier throttle is applied, this is because the lock-up clutch is fully disengaged to provide torque-multiplication (which is the torque-converters main task)."

This seems exactly like what I'm experiencing. The rough idle could be a separate issue. But, I think there's some validity to this Torque converter clutch thing.

Any suggestions on how to test for it and/or fix it?

Also I'll be scanning it on Sunday with a couple of hobby mechanics. Hopefully they'll be able to offer some answers.

Thanks!