Toyota Repair: engine miss, open wallet, toyota camry

Question
QUESTION: I have an engine miss at high speeds in my 2003 Toyota Camry XLE. There is not a check engine light on nor has there been one in the past according to the diagnostic at the dealer. They decided to change the spark plugs since I have 125,000 mi and they have not been changed. Cost including the diagnostic was $500. It did not fix the problem and am wondering if you have a clue as to what to check next. I am hesitant to go back there as I feel I have to walk in there with an open wallet.

thanks for your feedback.
sue

ANSWER: It's hard to say what may be causing this misfire without the check engine light turning on since engine misfires are closely monitored by the computer. When at higher speeds do you feel any vibration in the car at all?

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QUESTION: Thanks for responding so quickly.
As a mater of fact I do. I made a mental note to get the wheels balanced even I recently did that.

ANSWER: Thanks for the reply, we have seen some cases where out of balnce wheels cause a vibration which the same sensor that picks up engine misfires picks up the vibration and interprets this as an engine misfire so do have the wheels balanced and let me know if this helps at all.

---------- FOLLOW-UP ----------

QUESTION: Hello again -
I took my car back to the dealer but they cannot find anything wrong. They told me that they cannot diagnose the problem since there is no check engine light on now or in the past. They also said they test drove the car and cannot feel the miss. I feel it every day as do people who ride with me. hmmmm
I did have my wheels balanced yesterday. For some reason the front was   1 oz out of balance. I do still have the miss though it seems not as bad. This a.m. was the first long drive after the balancing. It starts haappening after 15 - 20 mins of freeway speed. Do you have any other suggestion?
thanks for sharing your knowledge.
sue

Answer
The dealer is partially correct, there actaully should be a check engine light when there is an engine miss, without having diagnostic codes it's anybody's guess as to what the problem may be and you certainly don't want to start replacing parts, the part I have trouble with is that a dealer technician or shop foreman don't feel the miss when test driving but you do, maybe because you drive this car everyday and they drive many different cars every day or maybe they just don't want to deal with this because they have no answer for you. My thinking since I first answered your question is that it is something other than an engine misfire. My best guess was the tire balance possibility since I have seen this before. Try to either have another dealer look at it or a reputable ASE certified auto repair shop, it's difficult to diagnose something like this without being able to drive the car.