Letters: Slipping tranny may need replacement

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Q: The transmission in my wife’s 2004 Chevrolet Impala (90,000 miles) seems to slip when taking off from a stop. It doesn’t do it all the time. The transmission fluid was changed at around 60,000 miles and the fluid level is OK. What could be causing this problem? —Darren, email

A: It could be that the pressure control solenoid is acting up. But because the labor time to replace it is listed at 4.6 hours and since the transmission has 90,000 miles on it, a complete transmission overhaul would be recommended.

Before you do that, though, you may want to try a transmission flush. Just make sure that the proper fluid is installed. Installing transmission fluid other than what the manufacturer recommends can definitely have an adverse effect on the operation. Other options include living with it until it gets worse or having the transmission replaced with a rebuilt unit.

Q: My 1996 Ford Contour has never idled smoothly when stopped. It has gotten worse and now my wife does not want to ride in the car. I have spent hundreds of dollars trying to fix it.

The car has had several fuel system cleanings and the mass air flow sensor was cleaned, too. The exhaust gas recirculation valve and air box have been replaced. Last October the check engine light came on and the oxygen sensors were replaced. There have never been any codes stored regarding the poor idle, and it has stumped the technician working on my car.

Recently the engine stalled when I was making a left turn. My technician told me to replace the Bosch spark plugs with Motorcraft platinum. He cleaned the throttle body and replaced the idle air control motor. Still, the idle is poor. The engine does idle a bit better when the engine is cold versus hot. Sometimes it needs a little push on the gas pedal to get it to start. But once the car is in motion it has plenty of power.

The technician smoke-tested the engine to see if there were any vacuum leaks and couldn’t find any. I don’t know what to do next. If not for the idling problem it’s a nice car. What do you think is wrong? — Ed, email

A: You mentioned that the MAF was cleaned. It might need to be replaced. But before replacing any more parts, the technician should check the engine for any mechanical problems. A compression test, cylinder leakage test and vacuum test should be performed to make sure the engine is in good mechanical condition.

If the engine is in good mechanical condition, make sure that there are no vacuum leaks. I know you said that the engine was smoke-tested but maybe something was overlooked. Another way to look for vacuum leaks is to feed a controlled amount of propane (from a hose attached to a bottle of propane) along areas of the induction system. Wherever there’s a leak, the propane will cause the engine speed to increase.

Maybe the throttle housing or throttle shaft are worn. If the engine is running OK and it’s just a bad vibration problem, maybe the engine or exhaust mounts are worn or something is making contact with the body that shouldn’t be. Leave no stone unturned if you plan on keeping the car. But to keep your better half happy, you may need to trade the Contour in for something else.

Questions for Ira Siegel? Call the Auto Advisor Hotline at (708) 633-6839 or e-mail ira.siegel.is@gmail.com. Siegel is an automotive instructor and an automotive service excellence-certified master auto technician.