I am getting a P0172 mil code (Fuel System Too Rich) on a 1996 Plymouth Neon SOHC.

So far I have replaced both O2 sensors, MAP/IAT sensor, the PCM, Fuel Pump, Fuel Filter, Spark Plugs, PCV, and Fuel Injectors to no avail. The car seems to run fine, but idles poorly once it has warmed up.

One thing I find strange is that my intake air temp is running at 190 to 230 degrees. Once the IAT gets past 120 the fuel trim starts to go negative and stays at -25, setting off my MIL. The intake pressure is fairly steady around 26hg.

Anyone have a suggestion? I am about to hold the radiator cap and replace the car under it.

 

Hmmm .... not exactly a flood of answers. However, since the weather got colder, a chilly 45 degrees for us desert dwellers, the check engine light went out. I haven't scanned it yet, but I have a feeling the cold air is masking my problem.

Can anyone tell me what the intake air temp should normally be above ambient once the car is warmed up and in closed loop? I still think this is related to my problem, but maybe I'm barking up the wrong tree [:-]

 

Did you replace the PCV valve? Also check your vacuum lines and brake booster.

If all this is good, then you could have a problem with your timing.

 

Yep, replaced the PCV and checked all the vacuum lines, but didn't check the brake booster itself. That did the trick. The second I pulled the line off the brake booster and plugged it up, it started purring like a kitten. Did a test on the brake booster and found it to be less than desireable.

Thank you much Das, I owe you one

 

Glad to help as always.