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So let's establish that I'm an idiot for rushing into things, I got it. This morning I decided it was time to upgrade my throttle body and plenum. Everything was going fine, plugged everything back in, and went to start the car. Now that brings me to my dilemma. Car cranks, but wont start. Here's the part where I explain as to why I'm an idiot. The whole time I was unplugging and plugging in stuff, I still had my battery hooked up, so my ECU must have started to freak out on me. Could that be my problem? It's cranking like it's thirsty and hasn't had any gas in days, and my fuel pump doesn't seem to be helping out much. I don't hear it when I turn the ignition to On. I checked the fuse and fuse is fine. I have a tuner with a few tunes, I restored the ECU back to factory settings (according to my tuner) to see if that helped any, but no luck. As I said, everything was plugged back in the right spot so that shouldn't be an issue. I even checked my coils and fuel rails and they were all plugged in and everything. Anyone?
The OP did not mention the model year of the car. However, for the 1999-2004 MY, the fuel pressure sensor is a NO START sensor. That is if the PCM does not receive a valid fuel pressure signal, the motor will crank but won't start.
Based on the work done, I would start there. Check the electrical connector to the fuel pressure sensor. Confirm that the intake vacuum reference line is connected and leak free.
Since you own a tuner, consider using it to monitor the fuel pressure. What is it? Also use the ODB2 scanner to monitor RPM's. Do they change during cranking? If so, that means the PCM is receiving a good CKP signal.
Next check the MAF value. Does it change during cranking?
I put tape around all the vacuum hoses to make sure there were no leaks or got detached in the process. I tried unhooking the battery for 30 minutes like twice, reset my ECU back to stock, also loaded an updated tune, no luck. Fuel pump is on and can hear it when the car is on the ON position, checked for tripped fuel pump in the trunk and that is fine as well.
Disregard everything I just said. It started right up. The solution?
I checked my TPS, and looked at the way it was supposed to go in. When I originally put it back on, I was unsure of how it was supposed to go in, so I just sort of winged it and put it in whatever way, totally ignoring the fact that it can only go one way. I heard a pop when I originally put it on but I didn't much of it. So I took it back out after hours of thinking and narrowing down the symptoms and stuff, and found out that the spring inside the TPS was broken, being the reason why my ECU didn't know if I was holding down the throttle or not. So I ran to AutoZone and bought one for about 25 bucks, popped it on and fired right up. This could easily have been avoided if I had just paid attention and not rushed into things like I did, would've been a 30 minute job instead of a 2 day job. Thanks wmburns you helped out a lot and all the other guys that gave me a better understanding.