I have a 2004 impala with just under 95k miles. Within the last month I've been having problems with the car starting after it has been running awhile usually have to crank in 2 or 3 times for it to start. When the engine is cold it starts right up. In the last week I've started to notice a gas smell coming thru the vents and by the engine compartment and also got a check engine light for small emisson leak. This past weekend my uncle and I checked the engine found no leaks in the fuel injectors and no leaks in the lines. We went to auto zone and the guy told us it had to be the fuel pressure regulator. So we purchased a new one and rented a pressure gauge tester. We hooked up the guage per the instructions and found the pressure to be at spec when engine was cold. we ran the engine for about 15min re tested and it held pressure till the engine cut off and it bled off immediately. we replaced the regulator and seems to work better but I have also noticed while in drive stopped at a stop light the engine is ideling rough. It goes from steady to high to low to steady and I can feel the difference in the brake pedal as far as firmness. Please help!!
We actually changed the plugs and wires about 6 months ago. Air filters changed with oil changes. still original fuel filter. We asked the guy at autozone if we should change that and replace the EGR valve he said no it wouldnt cause these issues. and it is the standard 3400SFI
the egr might but if you dont have any codes i wouldnt worry about it. i i think the 3.4 has the iac on the side of the tb, i would clean that good and the seat. if that doesnt help, try taking carb cleaner and spraying around vacuum lines and the intake with the engine running and listen for it to change pitch
Based on your comment about the brake pedal firmness, I agree with Justin this sounds like a vacuum leak. Spraying with carb cleaner will help to locate the leak since a leak will suck the cleaner into the intake manifold and you will hear a slight change in engine RPM'*.