Older cars have computer memory retention problems

January 17, 2009/Steve Tackett

MOTOR MATTERS ASK THE AUTO DOCTOR BY JUNIOR DAMATO

Dear Doctor: I have a 1986 Chevy Caprice with 4.3 liter V-6, throttle body injection. When starting it idles low, then idles very high using a lot of gasoline due to the extremely high idle. During the day the idle will gradually drop, then when it’s idling just right the “check engine” light starts blinking. If I turn it off then restart, the idle will be too high again. Hooking a diagnostic computer to it shows no error messages, but the diagnostic computer corrects the idle problem. When the diagnostic computer is removed, the idle returns to its extreme high idling gas consumption state. Any ideas? Jim
Dear Jim: It sounds like a vacuum leak at the base throttle body gasket. I have seen many over the years. The computer system in this car and all pre-1996 vehicles do not have the power to monitor and hold in memory fault codes. A technician that has knowledge of how the fuel injection system works and how to check using propane and a digital volt meter will be able find why the engine rpm is so high. A vacuum leak at the throttle body base, EGR valve partly open, lazy idle speed motor or throttle position sensor all contribute to idle speed.
Dear Doctor: After filling up my 2005 Chrysler Town & Country gas tank with regular gas, the minivan bucks and tries to stall out either on the property or out on the highway. Sometimes the engine just cuts out and stalls just wherever I am. After about 15 to 30 seconds it runs smooth again only if I rev the engine in gear or neutral and try not to let it stall out by pumping the gas pedal. What can I do to make it run smooth all the time? Ron
Dear Ron: It seems like unwanted gasoline is getting into the engine from the gas tank. There is one case on our Identifix web site of a faulty rollover valve on the gas tank. This will cause gasoline to actually be sucked in the EVAP system into the vacuum source and cause a rich condition. Have a technician check the EVAP system with a bi-directional scan tool. He will be able to activate the solenoids and valves for testing.
Dear Doctor: My 110,000-mile car has had a “check engine” for years. It always passes inspection and gets 26-28 mpg. The problem readouts are po133, po410 and p1133. What should I do? Ken
Dear Ken: A quick look on our Alldata and Identifix web sites, as well as actually seeing these cars in our shop indicate the following: The p0133 and p1133 are both oxygen sensor possibly related to poor ground connection, slow to respond O2 sensor, or a computer reprogramming. The p0410 is a secondary air pump or air pump check valve. A common problem is water ingested by the electric air pump, which would need replacement. Both failures need to be properly diagnosed before any parts are replaced.
Dear Doctor: I have a 2002 Cadillac DeVille with only 47,000 miles. When the “check engine” light came on my dealer said it was two things about my transmission. They ask if it had been shifting roughly and I told them no. A computer test showed two codes: P1860 (manufacturer control transmission) and P0741 (torque converter CKT performance or stuck off). What do these two items mean and what I should do? Melissa
Dear Melissa: This is a common fault in the GM transmission. It could be a faulty transmission solenoid, torque converter or major internal problem. There will need to be a full diagnostic check of the transmission circuit. Whatever the fault, if your state has a yearly emission test, then the car will fail the test if left untreated .
Dear Doctor: I have a 2008 PT Cruiser with 5,000 miles that is burning 1 quart of oil every 1,000 miles. The dealer said this is normal. What are your thoughts? Sal
Dear Sal: Some engines will burn oil during the break-in period. However, a quart every 1,000 miles with only 5,000 miles on the odometer is not normal. The oil that is burning off is contaminating the catalytic converter and all the oxygen sensors. A compression test, leak down test, a spark plug inspection, and PCV valve system test are needed to locate the problem.

Junior Damato is an ASE-certified Master Technician.

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Copyright, Motor Matters, 2009