My car stalls at idle when fully warmed up. Electronic diagnosis suggested O2 sensor. Sensor was just replaced and problem still persists. Check engine and fuel cut out light come on when this occurs. Car was not driven much in the last few months before I bought it.
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Check coolant temp sensor. These fail often and cause all kinds of mystery problems. This unit acts much like a choke on old carb engines and can fail in different ways. Most common (I think) they fail such that the ECU thinks the engine is cold when it has begun to warm and thus the ECU delivers too long a pulse to the injectors so that the engine runs way too rich. I think it is also possible for the sensor to fail at any point between cold and warm such that the fuel mix is wrong except for the particular temp at which the sensor is stuck. Also O2 sensor has some fuel "trim" input.
I don't know if this will help. Had a similar problem with a 99 Blazer.
Would drop to between 300 and 500 rpm at stop signs and red lights, would stall and shake.
Did all the same checks, replaced mass air flow sensor, replaced cam sensor, cleaned the fuel injectors but the problem was still there.
Replaced both #1 and #2 O2 sensors in the exhaust pipes and now the vehicle runs fine. The idle is back to a steady 750 rpm in all stopping conditions. The Mass air flow sensor and Cam position sensor get information from the O2 sensors.
the transmission replcement mechanic may have missed plugging the 02 sensor back up,or layed the 02 sensor wires across the exhaust system,which burnt the 02 sensor wires.they also may have missed plugging sensors back up. suggest you go back to replacement mechanic and have them explain to you why it does'nt run the same. but do not be fooled,somethings not plugged back correctly.i know budget living. is check engine light on? if so, auto zone and advance auto parts can diagnose with printout for free. no charge! hope this helps and thank you for choosing fixya.com us marine retired
I had same problems w/ my 99 Chateau 5.4L. EGR-Ensure port into intake and pipe from exhaust are clear using low pressure compressed air. Pull vacuum on EGR diaphram and ensure it opens and closes smoothly. If this checks out then problem is probably in the EGR sensor (mine had both ports and hoses clogged w/ aluminum corrosion from the sensor, cleaned out hoses and lines to exhaust pipe w/ compressed air, ended up having to change the sensor). IDLE AND O2 SENSOR- Caused by vacuum leaks in the PCV line (line is plastic wrapped w/foam insulation; was cracked under the insulation; both rubber end connectors at manifold and pcv valve were softened, collapsed and leaking; allowing excess air into the manifold after the mass air flow sensor which throws off the O2 sensors. engine computer does not read O2 sensors until after engine is warmed up which is why idle is fine until then).
It would be nice to know the past history of the car. For example, does the engine suddenly stall or does it slowly lose rpm and then stall, or does the car run fine and then sometimes idle erratically but never used to stall and now does. Can you wait 10-20 min and then it starts? etc?
Please check the Coolant Temperature Sensor (via an Ohm meter) for an Open circuit (infinite resistance) or possibly high fluctuation resistance.
Check that approx. +5V is present at the Sensor when ignition is on (engine Not running) by removing the connector and probing the connector.
Probe resistance during idle when engine is Cold and watch as the engine Warms to fully warm (normal) temperature. When cold, the resistance should be high (about 2K ohms to 4K ohms) and should decrease down to about .3K ohms fully warm (See page 6-8 in Haynes Manual).
If this issue is intermittent, it may be difficult to see it however large fluctuations in resistance when the engine is warm (1K ohm or so) could indicate the sensor is flaky. If the Sensor is open (infinite), replace the sensor.
Note: I don't recall for sure, but this error may be a "double trip" in that it is only logged if the issue occurs more than once (2+). Also, an error in this sensor is ONLY logged in the event of a short (0 ohms) or an open (infinite resistance) and is Not logged for erratic behavior.
Sounds to me like an O2 sensor, i had a similar problem with my Ford Probe GT. Luckily my car was a 5 speed so i just kept my foot on the gas a bit and put my car into neutral as i was slowing down or coming to a stop. If you're car is automatic I would not suggest doing neutral drops.. you'll cause more damage.