I have a theory about why my car is acting the way it is. Any input would be appreciated.

I have 3.42 gears, 700R4, TBI, 26"dia. tires. According to the calculators I should be turning about 2475 rpms at 80 mph. Instead I am turning much more than 3000.

Things to rule out: I bought a new tranny and new torque converter (both lock up style). After swapping the tranny and converter the problem still exist. The converter is locking up on both trannies.

My theory: Lately my car doesn't want to idle right. It idles high when cold (like it is suppose to) but when it warms up it doesn't drop. It is forced to drop when I put it in gear of course but still it isn't right. I'm thinking idle control valve. Could this cause my problem with the tranny too?

OR... could this be a speed sensor?

 

I would say that it is a speed sensor problem. I have a mechanical speedometer but I think that the 90 has an electronic one. Even though your speedometer says 80 you might be doing more than that which would cause your RPMs to be higher. Have a friend go 60mph or whatever and follow him with your car to verify that your speedometer is accurate.

 

"Much more than 3000" according to what? The trim package in the dash?

That thing is not an instrument. It's just interior trim, designed to give gratification to the buyer by waving up and down as the engine speed changes. It is not an accurate representation of anything. Even if it was accidentally accurate when new, they always fail, and they specifically fail by reading high. Sometimes twice the real RPM, and occasionally even more than that.

Before getting all worked up about transmission stuff and the like, find out what the engine RPMs really are, with a piece of real test equipment.

 

I did think of a bad tach but it just didn't seem likely. My speed sensor does leak oil from it which is probably just a bad seal I thought at first but after putting in a new seal it still leaks.

What kind of test equipment are you talking about? Another tach?