I hear ya, and thanks. But I never flew the planes, all I did was provide admin support for those that did. But I know the brave folks who did fly those planes, air fueling tankers. As one of them once told me, they are only 30 seconds away from being a smoking crater. Bravest folks on the planet, in my humble opinion.
Why isn’t intermittent weak ignition that occurs at high RPM in the list?
Because I probably missed that one? It’s now been added! 
EGR
MAP
TPS
ECU
Crankshaft position sensor
Bad timing
Timing belt misaligned
Kick down solenoid
Bad Ground
Vacuum leak
Fuel pressure
Intermittent weak ignition that occurs at high RPM
Oh, and someone else suggested the oil filter not being installed correctly
Now would be a good time to take your Corolla to a good shop. Leave the list at home. Describe the symptoms and they will troubleshoot it for you then fix it after you authorize the work. You should ask for an explanation of why they think their propose fix will work.
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I have an appt set for Monday at the local Toyota service center, and yes, I plan on leaving the list at home. Someone in a previous post said to do the same thing, so that’s what I’ll do. Thanks for the advice though, it’s much appreciated.
The big clue imo is that the symptom appeared immediately after the engine’s front crankshaft seal was replaced. Make sure the shop very clearly understands this important relationship.
For sure! I’m definitely going to ensure I make that correlation know to them. I’m hoping the problem is as simple as a sensor that was damaged or not hooked up. I’ll post back here to let you all know what they found, and thanks for all the advice.
If the sensor wasn’t hooked up, the engine wouldn’t start.
Tester
Hahaha, yep, see, this is why I appreciate folks like yourself being here. Newbies like me don’t the difference between the crankshaft sensor and the MAP sensor. I’d be completely lost! Thanks for helping me my friend. I’ll let you all know what they tell me tomorrow. I just hope that whatever it is, it’s not serious.
Well, that didn’t go according to plan.
I took the car to the Toyota service center, and after two hours of tests they really couldn’t come up with the cause of the problem. They “recommended” that I have a shim valve adjustment to start but they didn’t know if that would solve the problem. They said, basically, this is the next step to try and solve the problem but there were no guarantees. The cost would be $760. I told them I would have to think about this.
This bothers me because it looks like they went by a predetermined checklist to try and solve the problem instead of looking at it from “ok, the car didn’t have this problem before the oil seal was replaced. What could have happened to cause the problem now.” To me, that line of thinking would be more logical. Granted, they said they checked all the sensors via their computer system but if what many of you have said above is true, a bad sensor might not throw a code. Of course that makes it difficult on them because they would have to manually check the sensors that could have been affected by the oil seal repair, but that’s why I paid them $152. So now I feel I need to get another opinion on what could be the cause.
On the bright side, they checked other aspects of the car and they said it’s (mechanically) in very good condition. No leaks, tires are good. steering and suspension are good. So all I gotta do is get this issue fixed and I’ll be ok for a while.
Thoughts?
If it were my car? I’d change the crank sensor.
Tester
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I was thinking the same thing. I would rather have a $60 - $90 sensor replacement than spend $760 on a maybe repair.
Every Corolla model year tends to be a little different, but on my Corolla what that means I expect is they believe the valve clearances need to be adjusted. That’s done by replacing small metal discs (called shims) located between the camshaft and the valve. That decision is usually based on measuring the existing valve clearances, and comparing them to spec. Your engine has 16 valves, so all 16 are measured. For example the measurement for valve number 3 might be 1 mm, and the spec might be 0.5-0.8 mm. So the valve clearance for valve 3 is too loose, and they’d change to a shim 0.3 mm thicker. Before folks here can give you much advice on whether this is the issue, you’d have to post the current valve clearance measurement. Seems unlikely replacing the front crank seal would affect the valve clearances.
I diy’er measure the valve clearances on my Corolla every few years as part of routine maintenance. In 30 years, they have all been within spec. Although a couple of them are near the upper (too loose) limit.
If I had the problem you are having the three tasks I’d do first
- Disconnect & reconnect the crank and cam sensor connectors, checking for signs of pin or socket corrosion.
- If nothing found there, I’d verify the valve timing is correct. This means I’d remove the valve cover and the upper timing belt cover, which would expose the camshaft timing marks. I’d then rotate the crankshaft to its TDC timing mark on the compression stroke , and compare the camshaft timing marks to spec. This seems complicated, but in reality is on the order of replacing the crank sensor.
- If still no problems found, I’d replace the crank sensor on a hope.
They did say the timing was correct and that the valves are firing in the correct order. As for the sensors, they didn’t do a visual inspection. They just went by what their computer told them. Thing is, none of this occurred until after the oil seal was replaced so I would think, logically, that the problem has to center around whatever was moved or unplugged to make that repair. But since I’m not the expert I’m at the mercy of whoever tries to diagnose the problem.
There’s two separate types of timing that must be correct. The first is spark timing, and the second is valve timing. “valves are firing in the correct order” is an unusual thing to hear from a repair shop. “the spark plugs are firing in the correct order” is what I’d expect, referring to the spark timing. I’m guessing that is what they meant. It’s still an open question whether the valves are correctly timed. Your engine I believe uses a camshaft position sensor so they may have been able to determine the valve timing with their scan tool methods while checking the spark timing. Don’t know. My Corolla uses neither a separate crank position sensor nor a separate cam position sensor. Those timings are still required, but done by sensors inside the distributor.
If you hire this shop to set the valve clearances for $760, and that didn’t solve the symptom, I expect they’d fix a valve timing problem for you too, if they found one, w/no extra fee.
If you go back to testers diagram in post 17, you will see the relationship between the crank sensor and the balancer/oil seal. Dealer mechanics will be following the check list in the factory service manual. Just great if it is a constant problem.
Like I said I had a hesitation on a hard acceleration. Shop couldn’t find the crack in the crank sensor until it broke entirely. Then towed the car. Sensor in two pieces was then obvious.
I’ve followed those charts too and you can get to the bottom with still no resolution. Agree to just change the sensor. Cheaper than a tow and another diagnostic charge. I paid $80 for a five mile tow and lost a vacation day sitting in the shop watching tv and drinking coffee.
When I take it to the shop, I’ll mention that to the mechanic. Heck, if I could do it myself I’d get it done but it’s doubtful I can make that repair. Thanks for your advice, and I’ll let you know how things go.
If the problem also happens when revving up the engine while in neutral, then it shouldn’t be too hard to locate the problem. I suspect weak ignition, but weak ignition tends to show up under load and not when revving in neutral.
Someone should use a timing light on this car while the problem is occurring.
According to the folks at Toyota, the timing is fine. The problem started after the front crankshaft oil seal was replaced, so logically I would think it had something to do with that repair. Something got disconnected and not reconnected properly, or something was unknowingly broken during the fix and not discovered. I don’t know what parts on the engine were moved to facilitate the oil seal repair so I’m hoping another set of eyes will spot the problem. I’m inclined to believe the crankshaft sensor might very well be the culprit, but I’m also wondering if replacing the ignition coil and perhaps even the fuel injectors might be a good move in the long run. Again, I dunno. We’ll see what the mechanic says when I take it in on 1 Dec. In the meantime, I sit and languish at home, not wanting to take the car on any long trips on the chance that whatever is broken will break completely and leave me stranded somewhere. 
As I recall the dealership suggested to start w/ a valve clearance job for $760. Just curious, have you decided to forgo the dealership recommendation and instead your current plan is to take your car to a non-dealership shop for the diagnosis & repair? If so, what factors affected your decision?