Hello and thank you for taking the time to look at my post.
I have a few electrical issues in my 2005 ZX4 SES Duratec 2.0L with 140k miles. There is also a weird rpm bounce when the car is cruising at a steady rate.
First off, my "Check Fuel Cap", "Fuel Low", "Traction Control" (mine does not have a traction control system) all partial light up when the weather is either cold/humid/rainy. The "Fuel Low" and "Traction Control" lights only appear during heavy rain. The "Check Fuel Cap" light is almost always partially lit, except during summer.
Secondly, my main airbag light comes on as well as my passenger air bag off light is lit sometimes even when someone is sitting in the the seat.
Lastly, I have a CEL P0193 (Fuel Rail Pressure High Input). This is just within the last few months. I have one of those Bafx bluetooth OBDII readers and use Torque Pro to read codes and sensors. When monitoring the FRP (relative to manifold) it reads an average of 39 psi. It usually bounces around between 37-41 psi. I have seen spikes ranging from 50-60 and even 70 psi. On very rare occasions I've seen it sit at 50 psi for extended periods. I have spare FRP sensor and fuel filter waiting for be installed, but I do not have any experience with fuel system and have been putting off the fix. Sometimes the CEL goes off and the code changes from a current fault to a grey fault. I have a feeling my other electrical issues are linked.
My car's body is in pretty darn good condition. I am the second owner (bought at 50k in Dec 2010) and the last 30k miles and 4 years have been spent under a covered parking. I've never had an accident and there is not rust. However, a rodent has previously made a nest in the insulation for the engine bay firewall. This was about 2-3 years ago and was after any of this appeared, so I do not think it is relevant in any way. I have an aftermarket Alpine stereo, very mild, but it was installed by a couple of morons at Best Buy. I cannot remember exactly when (maybe 2013-14) or if the other electrical issues were present beforehand. I blame the lapse in memory on early college/twenties
Last year I replaced the whole intake manifold assembly. I didn't replace the throttle body. The manifold pressure sensor needs to be replaced, but I just can't seem to find the right part on eBay. I did this replacement because the swirl flaps were miles away from breaking off and killing the engine. I did get to scope out the top of the engine and it is perfect. Valves are completely spotless as well as the pistons. I only buy premium gas from 2 Chevron stations in my town. I have also replaced the motor mounts (holy crap, best investment ever), sway bar links (once at 90k miles and now at 140k), and rear shocks.
My alternator and battery failed summer of last year. I believe it started to slowly die around 2012. The car used to randomly die when at a stop and cold outside. My new one, according to Torque Pro, charges at 14.2V-14.8V depending on driving/load. The OBDII voltage, according to Torque, reads around 13.5V and varies the most.
I have a feeling there is a grounding issue somewhere... but the condition of the wiring and interior are making it really hard to understand where. Everything under the carpet looks like it is fresh from the factory.
When cruising, like 45/60, I notice a small weird surge. The feeling is like a small bobbing forward and backward. At the lower speeds I can see the tachometer bounce a needle width. At higher speeds I cannot see movement in the tachometer.
I hope I've not given you given you a migraine with this post and thank you once again for reading it. I just want to get down to the bottom of my issue(s). I love my car! I just dropped a very reasonable $200 on the motor mounts, sway bar links, shocks, and it feels so incredible. I just want to finish it off and have a normally functioning vehicle. I am an electronics engineering technician and very mechanically inclined, but I don't know where to start looking. Let me know if there is anything I can elaborate on and I appreciate all input!