Recently every time I turn on my mustang, the engine rpms go to 800 (as normal) and then suddenly drop to about 500, sometimes lower, after that it evens out around 900-1000 rpm. I live in florida so its not a temperature thing. I recently changed the fuel filter and cleaned the fuel lines with some cleaner. and my engine occasionally throws the code p0194 Fuel rail high input. Any suggestions? I have a code reader that can do freezeframe data if that helps at all.

 

http://engine-codes.com/p0194.html

Basically, it's an out of range fuel pressure sensing that's happening, and the causes are listed in that page. It could be a bad sensor, but it could be a bad fuel pump, bad fuel pressure regulator and a few other things.

Here's how to test it:

http://iihs.net/fsm/?dir=17

I... don't know if there's a way to put a fuel pressure gauge on the rails themselves to see what the actual pressure is. You might want to take it to a dealer or good shop to get this figured out. It might be as simple as replacing the sensor, but it could be a nice little goose chase too, so...

The idling could be a dirty throttle body, so cleaning it (with *throttle body cleaner*, not anything else) might be in order, and I've heard tell that the Mass Air Flow Sensor could cause that, so be sure to clean that too (with *mass airflow sensor cleaner*, not anything else!). When you do that, be sure to disconnect the battery first to let the computer forget how to run with the dirtied up sensors, it will NOT run right if you do not make it forget. Reconnect the battery after you're put back together, turn on, but do not start, the car. Wait for the dings and lights to settle down, then depress the throttle pedal in a run to WOT of about 5 seconds, then release. Start the car, go drive about for 8 minutes in normal traffic without the A/C, then 2 more minutes with the A/C on. Car is relearned, and hopefully better.

But the truth is if you have a fuel system problem, none of that cleaning is going to much matter, so be sure what it is. Cleaning them, however, won't hurt, and it's entirely possible that it could be causing the problem... unlikely, but possible.

Oh, and be careful, 'cause gasoline, and good luck!

 

Hey thanks a lot! I havent had any codes come up on the engine since the cleaning. I just cleaned the TB but wasn't sure how to make the computer re learn, Ill try it out and let you know.