Ok...I was able to test my theory out a little bit. The speedometer started working on my way home...just a few blocks...so I got on it a bit to see if I hit a rev limiter. The car did better until it got up to about 4000 rpms, and then hit a rev limiter again. Don't know if it's truly the VSS or not...may not be getting a consistent signal because of the corrosion. It almost seems as if the issue gets worse as the car warms up. Could it be the oxygen sensor? Something else??

 

Did the speedometer work perfectly during the entire test?

You can test whether the O2 sensor is causing the problem by unplugging it.

You might also want to check whether the cat is clogged.

 

Isn't that dangerous???

 

No.


Also check whether the cat is clogged.

 

The catalytic converter is brand new. I unplugged the O2 sensor...the idle was better and the car definitely had more power. When I really got on it I still ran into a low rev limiter.

 

Does the speedo act normally while the problem is occurring? If not, fix the speedo/VSS plu problem and then go from there.

You also may want to measure the fuel pressure and test the fuel pressure regulator.

 

The speedo didn't work at all this time...but when it was working the problem was still occuring.

 

My recommendation would be that you fix the VSS/speedo problem and then go from there.

 

Have you checked the timing yet?

Take your distributor cap off and check that your mechanic left the plastic insulator plate in place under the rotor. You should not be able to see the parts in the bottom of the unit, just a flat black plastic plate. Strange things can happen at high rpm without that.

I'd also do a basic dead cylinder check. Warm up the engine and let it idle. Disconnect one fuel injector plug and it should slow down / stumble. Reconnect that one and repeat with the other injectors. If you disconnect an injector and nothing happens, that cylinder is not firing.

The thing to watch for on the speedo is to see if the odometer keeps rolling normally. If it does, the sensor is OK and the problem is just the unit in the dash.

Cats don't clog up by themselves, continuing to drive with a problem with the engine is what ruins them.

 

Just curious, when you unplugged the O2 sensor, did the CEL remain on steady while you were driving and did you retrieve an O2 sensor CEL code? I am wondering whether the CEL is working.