Jim Grant's Tech Tips

‘90 Toyota Camry, Stalling Problem
Q: I have a’90 Toyota Camry 4 cylinder, automatic transmission with AC that has about 175k miles on it. The car runs well except for an intermittent stalling problem. The car will start and run normally until the temperature gauge starts to rise, at which time it will quit when the accelerator is pushed down. If I let go of the accelerator before the engine dies, the car will idle. If I nurse it through the "bad spot", the engine will pick up and run normal. Once the engine is warmed up past this point, the problem disappears. I have replaced the spark plugs, distributor cap, rotor and wires, checked the fuel pressure (it is normal even when the problem is occurring), replaced the fuel filter and checked the EGR valve. There are no fault codes in the computer, so I am assuming that the throttle position sensor, air mass sensor, oxygen sensor and other computer inputs are OK. This problem seems to be worse when it is damp outside, but I can't find any particular electrical problem. Is there any specific system that I should be checking that would cause this problem ?.....John

A: First, never assume that if there are no computer related codes, there is not a computer related problem. Because the dilemma is consistently related to engine temperature during warm-up, the coolant temperature sensor would be suspect. The coolant temperature sensor is a critical input to the computer. The computer uses this information to meter fuel, control spark timing, idle speed, emission controls, and with an automatic transmission shifting and torque converter lock-up function. I know I missed a few others. You can see how if the information provided by this sensor goes nutz so does your car! To prove or disprove the coolant temperature sensor, one must monitor voltage readings of the sensor as the engine warms up. This can be done with a good voltmeter or a labscope. What we often find is glitch (bad spot) in the sensor that only shows up at one point and then is gone as quickly as it came. Checking the coolant temperature sensor is a diagnostic step worth taking.