1993 Lumina 3.1L Transmission Problems

Hello.
I recently fixed my cars transmission problem. I got an update on the situation from the mechanic:

Service Description: Transmission shifting issue. Fluid level was checked and found to be full, also fluid condition is good. Road test revealed speedometer was inop and transmission went into limp mode. Also idle speed is excessive. System scan revealed Fault codes 24 and 35. Code 24 pertains to an issue with vehicle speed sensor signal and code 35 pertains to idle speed error. Scan data revealed PCM (computer) has idle speed control turned off in an attempt to control idle. Both issues can effect transmission operation, further testing is needed.
High idle issue and transmission control issue. Idle was found to manually set too high. When adjusted back to spec. engine stalls when put into gear. May just need to be driven so PCM can re learn base idle. Further testing of suspect circuits and components revealed intermittent operation of vehicle speed sensor. This would account for the intermittent transmission shifting operation. Recommend starting with speed sensor replacement and driving vehicle to see if idle stabilizes. After repair transmission operation was restored. Engine idle improved, however it surges a little. Due to oil contamination in throttle body a motor vac service is recommended in hopes to stabilize idle.
Disassemble as needed. Remove faulty sensor. Clean and inspect electrical connections. Install new sensor, Verify proper operation.

The mechanic suggest I tackle my oil leak problem next by having a motor vacuum service on it. He had told me that oil leaked at the valve cover and oil pump drive. Also, that there was a possible leak at intake manifold as well. And that the main wire harness was badly contaminated with oil.

Edit: Transmission is working now but car needs work to "stabilize" it. Need help taking course of action or suggestions Please and thank you.

Thoughts?

TLDR: Car is having transmission problems. Worth fixing or moving on?
Stop guessing. Have someone reliable ACTUALLY DIAGNOSE WHAT IS WRONG.

Transmission not shifting could be as simple as a fluid leak leading to low trans fluid level.

You had the water pump replaced. Now the "thermostat" doesn't work? Take it back and see what they screwed-up. First Guess: They failed to get all the air out of the cooling system. (There could be other causes.)

Stop guessing. Have someone reliable ACTUALLY DIAGNOSE WHAT IS WRONG.

Transmission not shifting could be as simple as a fluid leak leading to low trans fluid level.

You had the water pump replaced. Now the "thermostat" doesn't work? Take it back and see what they screwed-up. First Guess: They failed to get all the air out of the cooling system. (There could be other causes.)
Thanks for the reply.
The nearest mechanic to me is a Milex. $50 for a diagnostics. I trust local mechanics more than these "franchise" ones. Too bad all the local mechanics are on the other side of town. I'll take the car tomorrow and see what they say. I'll report my findings go from there.

So I took it to the Milex. The mechanic is saying that my transmission seems good. He told me that it's computer problem. Also that my engine is idling high and that might have caused it.
My engine has always idled high. I wasn't sure if this type of model controlled the transmission with it's "computer".
He's charging me $200 just to continue diagnosing the problem. Does that sound about right? I won'tfind out more until friday.

Get everything in writing. The terms of the diagnosis, the diagnosis itself. I'd expect the diagnosis to be "guaranteed" to fix the problem(s), if it isn't guaranteed to fix the problem, it's a guess, not a diagnosis. Guesses should be free.

Then, get the estimate for the repairs in writing. Again--guaranteed fixed.

Just wanted to update my progress on the car.
Here's the run down from the mechanic. :

Service Description: Transmission shifting issue. Fluid level was checked and found to be full, also fluid condition is good. Road test revealed speedometer was inop and transmission went into limp mode. Also idle speed is excessive. System scan revealed Fault codes 24 and 35. Code 24 pertains to an issue with vehicle speed sensor signal and code 35 pertains to idle speed error. Scan data revealed PCM (computer) has idle speed control turned off in an attempt to control idle. Both issues can effect transmission operation, further testing is needed.
High idle issue and transmission control issue. Idle was found to manually set too high. When adjusted back to spec. engine stalls when put into gear. May just need to be driven so PCM can re learn base idle. Further testing of suspect circuits and components revealed intermittent operation of vehicle speed sensor. This would account for the intermittent transmission shifting operation. Recommend starting with speed sensor replacement and driving vehicle to see if idle stabilizes. After repair transmission operation was restored. Engine idle improved, however it surges a little. Due to oil contamination in throttle body a motor vac service is recommended in hopes to stabilize idle.
Disassemble as needed. Remove faulty sensor. Clean and inspect electrical connections. Install new sensor, Verify proper operation.

My engine cut off while I was driving. I switched the battery since the old one was weak hoping this would fix the issue. Driving home today the engine cut off again. The mechanic had suggest I clean out the motor since my car leaks oil pretty badly. Would this affect my engine cutting off if oil was leaking somewhere it shouldn't be?

My engine cut off while I was driving. I switched the battery since the old one was weak hoping this would fix the issue. Driving home today the engine cut off again. The mechanic had suggest I clean out the motor since my car leaks oil pretty badly. Would this affect my engine cutting off if oil was leaking somewhere it shouldn't be?
A "dirty" throttle body can cause idle/stalling problems. Won't hurt to clean it. Might help.

Wantes to update my situation again. Car seems to be working fine now. Thanks for the help.
Now I just gotta find this damn oil leak.

The typical oil-pump-drive O-ring?

http://hbassociates.us/Lumina_Oil_Pump_Drive_01.JPG

The typical oil-pump-drive O-ring?

http://hbassociates.us/Lumina_Oil_Pump_Drive_01.JPG

Yeah. I got quoted $700 to fix it. Not worth the money. I'm hoping the car will run until i get enough to buy another car.

Yeah. I got quoted $700 to fix it. Not worth the money. I'm hoping the car will run until i get enough to buy another car.
Fix it yourself? The instructions are on this web site. I've patched 3.4Ls, and repaired one for real when I had the heads off. Never done a 3.1, though.