[twobjshelbys]

Originally Posted by 169mph

Thanks for the response.

It usually idles at 1050-1150 rpms. The rpms start dropping after it's been running for a few minutes. They'll drop until the engine almost stalls then they go back up normal for about 20 seconds and then the RPMs drop again. It's a cycle. Eventually the engine stalls. I keep the RPMs up when I go for drive but that gets old quick.

I have a Walbro 255 in-tank fuel pump, which I plan to switch to an aeromotive 340. I going to replace the fuel filter downstream of the pump when I switch fuel pumps.

I had issues with backfiring when decelerating in the past but after replacing the exhaust flange gaskets it rarely happens. Could an intake manifold vacuum leak cause the idle issues?

Backfiring when decelerating was the primary clue that my fuel injection was set way too rich and the cause was a failure to populate the altitude adjustment table. What fuel injection controller do you have? You should be able to connect to it and monitor AFR. Where is your O2 sensor? Mine was in the passenger side exhaust. It is easy to confuse the O2 sensor (and thus the AFR) if the sensor is too close to the end of the tailpipe since air gets back into if there isn't enough exhaust flow. My headers had a O2 sensor bung closer to the engine (but only one cylinder). The muffler location allows for the blending of one side (if the other side is off, you've got bigger problems) but the backflow can confuse it. If you have a single bung, try moving the O2 sensor there and see if the symptoms change.