Transmission Second Gear Shutter
Q: I have an '02 Chevy Silverado with about 20,000 miles on it. When shifting between first and second gear, it shudders. The warmer the truck gets, the more and harder it shudders. I took it to the dealership, and it's putting in a new wiring harness from the alternator to the transmission. Have you heard of this problem before? Will the wiring harness fix it?
A:The repair won't require the replacement of a complete wiring harness, but does involve a new connector along with the repositioning and addition of a few wires on the alternator circuit. It seems that the electrical feedback involved with the original routing of the charging circuit interfered with the operation of the transmission-pressure control solenoid. This resulted in a fluctuation in line pressure and produced the shudder from first to second gear, which brought you into the service department in the first place. Chances are it did a quick test to corroborate the diagnosis by simply disconnecting the alternator and taking a test drive to confirm the elimination of the 1-2 shudder. The condition may affect certain '01-'03 Chevy Silverados and GMC Sierras and is documented in Chevy Technical Service Bulletin 02-07-30-030.
Sticky Throttle Buildup
Q:I own an '01 Dodge Ram 1500 4x4 pickup with a 5.2-liter V-8 engine, automatic transmission, and approximately 58k miles. The throttle has been sticking open for less than a few minutes each time. Finally, it stuck open longer, and I took it to a local Dodge dealer to see what was causing the problem. They found a buildup of carbon on the inside of the throttle body and advised me that it could be cleaned to eliminate the problem. Everything seemed fine for a few months until the throttle stuck open again. I took it back to the dealership, and they had to clean the throttle body again and also replace the IAC motor. What can be done to take care of this permanently?
A:Excessive carbon buildup within the throttle body is a common event that can almost be considered a normal maintenance item. The carbon may prevent the throttle plates from seating properly in the idle position and therefore result in a higher-than-normal idle speed, which is ordinarily controlled by the powertrain-control module. I don't see how an undue amount could have accumulated in such a short period of time and require another cleaning. A faulty IAC (Idle Air Control) motor is another possible cause of an intermittent high idle, and perhaps its replacement the second time around has corrected the problem. The IAC is a computer-controlled valve that varies the amount of air bypassing the throttle plates in order to regulate idle speed. If the condition reoccurs I'd suggest a detailed inspection of the throttle body assembly, springs, linkage, the throttle cable, and anything else that may have prevented the full seating of the throttle plates. Abnormal wear of the throttle body itself is a possibility that would require replacement of the entire assembly. Of course, there are lots of other potential causes, ranging from a vacuum leak to an intermittent data sensor signal causing the PCM to raise the idle speed at incorrect points in time.