My sister recently bought herself a 1997 Toyota RAV-4 which dies when it’s cold. Dies, restart it, dies, restart, etc, until about the first stop sign, at which point it’s apparently warm enough to run without dying.
She had the oxygen sensor replaced, and the distributor cap and wires, which didn’t fix the problem. The reason the oxygen sensor was replaced is that her mechanic checked the codes. (Whether it showed any other codes, I don’t know.)
Now she wants me to take a look at it, and I hate to disappoint her. What sort of things should I be looking at/for?
How does the fuel injection know when the engine is warm–by the same temp sensor that drives the gauge, or by a separate switch? (Actually, I don’t even know if it has a gauge.)
While the car may have had a code for the O2 sensor, I can state for sure that the O2 sensor is NOT causing a cold start stall problem.
O2 sensors don’t come on line until a preset engine coolant temperature. On a Volvo that temp is 60C. Figure room temp is about 20C and in the winter parked outside it will probably be way cooler than that.
The O2 sensor code could also be the result of another condition, not the cause of the problem.
How do it know engine temp? Despite it rather misleading name, the Engine coolant temperature senor (ECT) sends this information to the engine control module. It is possible that the ECT is registering too warm a temp, causing the system to run lean, and stall cold.
Other causes include (In no particular order)
Dirty injectors that don’t correctly atomize the fuel
Mechanical issues with the engine itself.
Air leaks in the intake system
Fuel pressure problems.
Bad MAP sensor (If equipped)
Bad MAF sensor (If equipped)
Bad mapping in the ECU
Sticking idle air control valve.