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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
I hear ya. Some people seem to thrive on it, but I'd probably go nuts myself.
All your suggestions seem to be focused on the engine itself losing power; I'm intrigued that you seem to discard immediately the transmission. I like that; it could be good for my wallet :-)
Fuel line leaks sounds like something I can begin to check as soon as it's light out. I haven't smelled gasoline, but now I'll be looking for it.
Loss of spark is intriguing too; the symptoms are soooort ooooof like the ones I had when my distributor wiring harness had gone flaky and one or more cylinders were either misfiring or not firing at all. No backfires, though, with this symptom set, while the distributor wiring problem gave me some of those.
Not sure how varying my speed would make the problem go away if it were a partial blockage somewhere in the exhaust system. (On Monday night's drive, once the problem started, the only time it went away was during speed variation. Gah, that was tough, paying attention to the road and keeping continuous changes in speed going, when I was very very tired. Then Tuesday, after the car had sat around a while, it was behaving nicely again.) Will noodle more on that.
Mucho thanks for the brainstorming!