Q I have a 2001 Dodge Durango with 4.7-liter, V-8 engine with 105,000 miles on it. I am having an idling problem on a cold start. The idle revs up past 2,000 rpm, and then fluctuates back and forth a few times, and then goes down to the normal idle. This only happens on dry, cool days and when the engine is cold first thing in the morning. When the engine is warm or if it is a hot, humid day, the idle is normal. I brought it to a Chrysler dealer and, of course, it didn’t do it there (I even left it there overnight). Other than this problem, the car runs fine and still has a lot of life.
— T.D. Rocky Hill, Conn.
A We have a hunch the idle air control is sticking. Over time, carbon builds up on the IAC pintle and its seat. On wet, humid days, the carbon may be softer and the IAC less likely to stick. Normal throttle-body cleaning usually does nothing to clean the IAC. It should be removed for cleaning, and its seat in the throttle body should also be cleaned before reassembly.
Q The air conditioning goes out after a trip that’s two hours or longer in my 2006 Buick Terraza minivan. It has been at the dealer three times, and the computer module was adjusted, but the problem continues. After my fourth attempt, the dealer stated that the air conditioning unit freezes on long trips, and you just have to live with it. He said that it’s a known problem and that there is no fix. The vehicle essentially has no air conditioning after two hours of usage. Do you know if this is a problem with GM vehicles and the consumer has no work-around?
— G.W., Western Springs, Ill.
A Air conditioning that gradually decreases performance, and often stops blowing cold air, is a classic symptom of the evaporator icing up. Moisture normally collects on the cooling fins, drips to the bottom of the housing, then onto the road. You commonly see water under a vehicle when the A/C is in use.
If the water can’t get out, it will freeze, and the ice blocks airflow. You could turn off the A/C until the ice melts, but for a permanent fix, the drain hose, the housing or both may need to be cleaned out.
Q I have a 2004 Ford F-150 4X4 FX4 that has had a rear-differential problem since I bought it used with 16,000 miles. It has a limited-slip-style differential that seems to slip a little on takeoff. I have taken it to the dealer, only for them to tell me they can’t duplicate the problem. I found a technical service bulletin that refers to a shudder (which I had as well) and a binding sensation. I have an extended warranty, so the dealer performed the TSB, but the problem remains. What about changing the oil from a synthetic to a non-synthetic? Would that help?
— J.L., Louisville, Ky.
A The service bulletin you provided calls for replacing the clutch pack for the differential. It goes on to state that 75W-140 gear oil should be used in place of the original 75W-90 lube, and that a friction modifier must be added to the lube. You can try a different lube, but we can’t vouch for its effectiveness, and it may contaminate the friction material on the clutches.
Bob Weber is an ASE-certified master automobile technician, having recertified every five years since 1978. Address your questions about cars and trucks to Motormouth, Rides, Chicago Tribune, 435 N. Michigan Ave., 5th Floor, Chicago IL 60611, or e-mail motormouth.trib@verizon.net.
