My 94 Z28 has about 60k on the engine and has been running great! A couple days ago it started running a little rough, and I could smell gas. Then it had trouble turning over to start and I while starting it I had to tap the gas to get it to go. It starts but is rough, the RPM's jump between 500 and 1000 until it works it's way through whatever the problem is. It's fine at high speeds and doesn't die at a stop but just feels rough and is running rich. Plugs were changed in Jan, I visually checked vacuum lines and didn't see issues there either.
Ideas?

 

Does it hesitate any? if yes check your plug wires, and fuel filter. Otherwise check your fuel pressure and your distributor.

 

sounds like your running rich alright, check fuel pressure, check for any sensors unplugged, scann for trouble codes

 

If continually running rich, might check the two-wire coolant sensor for the PCM as it may be open, showing a high resistance across its two terminals indicating to the PCM the engine is really cold.

After running for 90 seconds approximately, the sensor should read below 5Kohms.
Also, low/no spark to the plugs can cause this also. Might need a new ign module or a new Opti-sensor distributor since the engine is a LT-1.

 

I took it out a couple days ago, just to see how it would drive. It was rough and rich and did hesitate, even back fired, which I have never heard it do.
I'm pretty sure the plug wires were replaced when the engine was changed. I will check them thoeugh and look at the fuel filter.

 

check fuel pressure, both low and high fuel pressure can cause a rich condition

 

I wonder if I drove it about 8-10 miles to have the codes and fuel pressure check, would that damage the engine or the plugs? I haven't driven it since Friday and that was only about 3 miles. It seemed ok for a few minutes, had ok response, then acted up. I took it right home. This engine is still under warranty but it could be voided out if gas mix is wrong and causes damage.
What do you think? And thanks for the info so far. If the fuel pressure is an issue is that a sign of a bad fuel pump?

 

fuel pump or fuel pump regulator. testing fuel pressure is not hard, you can usually rent a fuel pressure test kit at local parts store, most rent for free but require a deposit. not sure i would trust the car for 10 miles, you may end up with a tow bill bigger than the repair cost.

 

sounds like my 3800 before I did the tune up. check the wires really good. run it at night. helps see if they're arching. if you do have to replace them I'd go with either accel or msd for plug wires.

 

Other than the after-firing (back-firing is out of the intake), that's how my LT1 was behaving with a bad opti.
And there are different degrees of badness an opti can achieve.