[drmalito]

After a cold soak (8+ hours w/o starting the engine), I have the weirdest thing in my rig. The engine starts ok, but right after starting it the RPMs sink to 500, stays there for like 2-3 seconds, and then it goes right up again to 1500 RPMs. I've noticed that the drop in RPM doesn't happen with a warm engine (between 1-5 hours of engine shutdown).
My question is: Could it be a faulty oil pump, faulty O2 sensor(s), or what...
I'd think that the problem is oil related (oil not flowing as fast as it should).
Any suggestions???

The rig has 140k miles on it.

Thanks...

 

[drmalito]

Because a couple of months ago I took my truck to Schucks, borrowed the scanner and it gave me a code (P0171 or 175 or P0325, I don't remember which one) but one of them had something to do with bank 1 being rich. Since I bought the truck, the 02 sensor was begining to fail. So my guess was that because of the fact that I will have to replace the 02 sensor, the old one was getting worse, and the result is the RPM problem. But who knows what the problem is...
Maybe it goes away after replacing the 02 sensors...