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The car: 1989 Toyota Corolla, automatic, 119K miles on it.
The symptom: Momentary power loss, less than a second long, at intermittent and hard-to-predict intervals. For a while it seemed to happen mostly near speeds where the transmission should shift, but now it isn't doing that any more. Most recently it's happened in a fast cruise -- when driving on a highway for twenty minutes or so at 70MPH, the car started having these little power pauses, and they increased in frequency rapidly to the point where the ride felt almost like a rough road. I varied my speed in response to this, moving briskly between 65MPH and 75MPH, and it stopped. It seems to happen much more when the car is warmed up than when it is not. I don't know for sure whether it's the engine or the transmission. I am guessing that it isn't something obvious, though, because this symptom has persisted through one visit to a well-recommended shop.
The question: What are ALL the things this could be, including some off-the-wall ones if they're possible, and how can I narrow it down a bit with some tests and inspections?
I don't have good jacks, nor do I have an engine tachometer. I can think of a good use for an external engine tachometer right away, but I don't have one handy. :-(
The symptom: Momentary power loss, less than a second long, at intermittent and hard-to-predict intervals. For a while it seemed to happen mostly near speeds where the transmission should shift, but now it isn't doing that any more. Most recently it's happened in a fast cruise -- when driving on a highway for twenty minutes or so at 70MPH, the car started having these little power pauses, and they increased in frequency rapidly to the point where the ride felt almost like a rough road. I varied my speed in response to this, moving briskly between 65MPH and 75MPH, and it stopped. It seems to happen much more when the car is warmed up than when it is not. I don't know for sure whether it's the engine or the transmission. I am guessing that it isn't something obvious, though, because this symptom has persisted through one visit to a well-recommended shop.
The question: What are ALL the things this could be, including some off-the-wall ones if they're possible, and how can I narrow it down a bit with some tests and inspections?
I don't have good jacks, nor do I have an engine tachometer. I can think of a good use for an external engine tachometer right away, but I don't have one handy. :-(
no subject
You've been given lots of advice, and some of it is pretty good, in particular fuel or electrical problems. The fact that the cut-out is associated with shift suggests that vaccuum-actuated devices associated with the RPM of the motor are failing to work.
Could be:
--Vaccuum advance on the distributor (assuming you have a distributor, not electronic ignition).
--Various vaccuum-actuated devices on the carburetor.
I would say also, don't discount the beginning of some kind of fuel pump failure. It is difficult for me to imagine it being something with the transmission.