1999 Cadillac Seville STS help...?

It has 124xxx miles on it. I was driving last night and the service engine light came on. I took it to my mechanic today who ran the codes and came up with: 1. Misfire Cylinder 4 2. Bad T.C.C. solenoid He said I would probably need a tune-up for the misfire but I have papers from the previous owner showing... show more It has 124xxx miles on it.

I was driving last night and the service engine light came on. I took it to my mechanic today who ran the codes and came up with:
1. Misfire Cylinder 4
2. Bad T.C.C. solenoid

He said I would probably need a tune-up for the misfire but I have papers from the previous owner showing that it had a tune-up done less than a year ago.

As for the T.C.C. solenoid, I understand is a common problem with these cars. From what I have read on the internet is that your car will stall at 25-30 mph and you will get worse mpg.

I noticed today that my avg mpg went from 18-20mpg to about 16-17. I know that having the Service Engine Light on will cause the car to go into limp mode and cause bad mileage.

He erased the codes to see if it comes back on.

Since he erased the code my car should not be in limp mode correct?

If that is true, then if my car still gets bad mileage then the solenoid is to blame even if my car doesn't stall?

Also, he said it would be best to rebuild the tranny but I read you can just replace the solenoid which would be less than 1k w/ labor.
Update: So, if it wasn't in limp mode, then my TCC is bad since I am getting worse MPG?

Even though it is not stalling? *knock on wood*
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