'95 Toyota Takoma Hesitates off Idle


#1

My 2.7 L Takoma hesitates to the point of stalling if accelerator is pushed moderately or hard from idle. If the accelerator is eased, the truck runs fine. Seems to run well at higher RPMs. What could cause that?



A little background that might be helpful: Long story short, had bad O2 sensor that I failed to replace fast enough, which resulted in a burned out cat. Replaced the sensor, but drove with the bad cat for a long while. Eventually, number 1 spark plug electrode insulator broke, which motivated me to replace cat and plugs. Check engine light immediately went out when new cat was installed, but noticed hesitation ever since. Thought computer needed time to reset itself, but so far no improvement.


#2

The off idle fuel trim is commanded by the Throttle Position Sensor (TPS) in open loop. So have that looked at. Also if this has a Mass Air Flow sensor check to make sure that the plumbing to it is intact and that the sensor elements are clean.

Please post back on any results.


#3

And check/replace the engine coolant temperature sensor. If it indicates that the engine is cooler than it actually is, the engine computer control may never go into closed loop operation. The engine would, then, run overly rich and could carbon up the catalytic converter. And, the fuel mileage would suffer.


#4

OK, thanks. I have the Toyota shop manuals, so shouldn’t have too much trouble finding the test procedure for the TPS, and tracing the plumbing to the Mass Air Sensor. I’ll post my results.


#5

Thanks for suggestion. The truck has the problem even when first started, when the engine is expected to be cold, so I’m thinking problem is probably not with the temp sensor.