89 Buick centry 6 cylinder 3300,at highway speed usually 55mph the care misses. What are the potential causes. I thought the O2 sensor may cause this problem. As it does not occur when the car is cold.

the one behind engine if you have a six cylinder. if you have four cylinder in front of engine

If you had a emissions problem and it has been corrected and the check light is out, then it should be cleared after 200 miles.Or will just show is a inactive fault

Yes, O2 sensor may sometimes lead to engine stalling. But also make sure that the MAF sensor is working properly. Better check for codes if the CEL is blinking.

I would check the fuel pressure with a gauge first. Assuming the check engine light is not on.
You didn't say if it is the 4cyl or V6, but both have plug wires and coil packs that could be failing. Even the crank sensor could cause the problem at high speeds and under a load.

P0302 TOYOTA - Cylinder 2 Misfire Detectedhttp://engine-codes.com/p0302_toyota.htmlForum CodePossible causes- Faulty spark plug 2
- Faulty ignition coil 2
- Ignition coil 2 harness is open or shorted
- Ignition coil 2 poor electrical connection
- Clogged or faulty fuel injector 2
- Injector 2 harness is open or shorted
- Injector 2 poor electrical connection
- Improper spark plug 2
- Insufficient cylinder 2 compression
- Incorrect fuel pressure
- Intake air leak
P0135 - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1http://engine-codes.com/p0135.htmlForum CodePossible causes- Faulty Heated Oxygen Sensor (H2OS) Bank 1 Sensor 1 circuit
- Heated Oxygen Sensor (H2OS) Bank 1 Sensor 1 circuit open shorted to ground
- Heated Oxygen Sensor (H2OS) Bank 1 Sensor 1 circuit poor electrical connection
- Heated Oxygen Sensor (H2OS) Bank 1 Sensor 1 circuit fuse
- Faulty Engine Control Module (ECM)
Tech notes The code means that there is a problem with the heater element circuit of the heated oxygen sensor. The Engine Control Module (ECM) monitors how long it take the sensor to warm up and start sending an adequate signal. The code means the the sensor is taking too long to warm up. Replacing the O2 Sensor 1 usually takes care of the problem
P1705 TOYOTA - Direct Clutch Speed Sensor Circuit Fault.
This is related to the sensor that gives info about the slippage rate o fthe transmisssion to the Transmission Control Module..

indicates injector problems and possible low fuel pressure
run the fault codes to check for EVAP and blocked cat converters

This is usually a sign of a bad crank position sensor ( first choice ) or cam position sensor.

Also a problem with the antitheft system or alarm immobilizer will do the same thing.

Take the car to Autozone for a free scan and try to get more specific identification of the cylinder number and the bank number for the O2 sensor. I would go after the misfire problem first to see if that cleared the O2 code. Hope this helps!

The #6 cylinder is the last cylinder on the right side while you stand in front of the vehicle. Firing order is 1 - 6 - 5 - 4 - 3 - 2. Potential cause and best case scenario is you have a defective spark plug causing improper ignition. Another scenario is the #6 coil pack is defective. If you have not replaced the spark plugs (30,000 mile intervals), then the issue may be just the spark plug(s).

Make sure you do not have any vacuum leaks and the egr is functioning properly. Next do a compression check and see if you have a low or dead cylinder. I hope this helps you to find your solution. Merry Christmas! and God Bless!