I had a code 44 which is lean exhaust. I lookede it up and it said to replace oxygen sensor and to chek for vacuum leaks. I did just that and still it is running at about 400rpm and is falling on its face when I hit the gas. Whats wrong? HELP

 

Try checking your fuel pressure. If you have low fuel pressure (bad fuel pump or possibly fpr, not sure if fpr can cause low fuel pressure though) that could cause a lean condition. I got a code 44 when my O2 sensor was bad and my exhaust smelled very rich (another indicator that it was the O2 sensor and not an actual lean condition) If your exhaust didn't smell rich then it probably wasn't the O2 sensor. The computer will try to compensate for the perceived lean condition by increasing the fuel delivery, ultimately ending in a very rich condition.

Code 44 & rich exhaust: Likely bad O2 sensor
Code 44 & not rich exhaust: Likely an actual lean condition, problem with the fuel delivery system. Clogged injectors, bad fuel pump

 

I checked my fuel pressure and It was fine and the injectors are OK also. My fuel pressure regulator is also fine. I replaced my O2 sensor already and it didnt help, However the code and service engine soon light went away. I still have a problem though. It still runs rough and dies on starup.

 

Have you checked your TPS voltage and IAC? These can affect startup, idle, and throttle 'feel'. There is a tech article on this site documenting how to check both of these.

 

Try disconnecting the MAF Sensor harness, see if she runs better.

 

Before you spend 10 months like I did looking for an elusive code 44. Check the intake manifold tork bolts for tightness. Mine were extremely loose.

All of the above suggestions are also correct.
O2
Vacuum Leak
Check TPS voltage. (5.6 I believe)
Clogged Fuel Filter
Low Fuel Pressure (unlikely).
Dirty Injectors.

Additionally:
Plugged muffler or cat
Leaking air diverter valve.
Bad PROM (false codes).

~~~~~~~~~~~~~~~~
<FONT SIZE="2" COLOR="red">Red 86 T/A</FONT><FONT SIZE="2"> 5.0 TPI</FONT><FONT SIZE="1"> </FONT><FONT SIZE="2">(LB9/WS6)
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looking at older posts. Was the exhaust plugged by any chance??