So last night, I was on my way back home and upon startup, it was running rough. It smoothened out and drove the two miles to get back home. Then hooked up my scan tool to my phone. Scanned codes and p0172 and p0175 were set. Looked at my AFR and it was at 11.4

Started diagnosing it about an hour ago. Fuel pressure at key on is 39 psi. Running at idle is 36 psi. No raw fuel in the fuel pressure regulator vacuum line. When turning the car off, fuel pressure was 36 psi and it went up to 40 psi in about 10 minutes. Weird. Really, no amount of fuel pressure leakage was showing.

Let the car warm up, as that was when the problem showed itself yesterday. With a warm engine. Then it went into fail safe mode at about 194 degrees Fahrenheit. I put it into drive, and it slammed into gear hard. I'm assuming it did that because of it being in failsafe mode. So I checked codes again and a p1121 showed up. Here are some screen shots I took while scanning. Any help is greatly appreciated.

 

Fuel pressure is low, but not extreme. Fuel trims indicate lean condition, either due to lack of fuel or air leak. Check the bellows of the inlet hose fore cracks and also the gasket at the throttle body. A vacuum leak is also possible. I the pump were failing or filter clogged I would expect poor acceleration.

 

Er... RICH, not lean.

MAF looks to be over-reading.

PCM trusts it to be approx correct so will be putting in fuel to match.

Then finds it's added more than is actually needed i.e. running rich because the MAF value is wrong.

Do some basics: clean the MAF, replace the fuel filter, then re-check the readings for MAF & fuel pressure. Oh - make sure the air filter is OK (correct kind, clean, not an over-oiled K&N for instance).

I'm uncertain what P1121 is on your car but if it's about the TP and MAF being inconsistent then it may have flagged the TP when very possibly the MAF is the culprit.

 

Yes, rich. I must have been half asleep. The MAFS does look like a suspect. If you decide to replace it stay away from cheap chinese knockoffs.

 

Does it matter what year x308 the sensor is listed as? I see on rock auto, they only list one for a '99.

 

Put a new MAF from o'reily. AFR's are not rich anymore. They stay between 14.5-14.8. Don't have time to wait on ordering because I need to get the car inspected. At 185 degrees Fahrenheit, the car went into failsafe, gearbox fault and so on. Scan codes and got a p1121 and a p1222. When the car went to failsafe, the idle jumped up to 1118 rpm and the MAF was reading 12.56 g/s. I checked battery voltage before doing a hard reset. It was at 12.08. But yes, I did do a hard reset. And obviously the car still started with that battery voltage.

 

12.08 is near dead and could be causing all manner of issues.

You need it charged fully and to be sure it holds the volts above 12.6.

 

Got the battery charged. Battery tested fine. Date code on it is December 2015. It was at 12.44 volts, but when I connected the positive and negative cables, it went down to 12.4 volts.

Car still goes into Failsafe, gearbox fault etc at 185 degrees fahrenheit. Also threw the p1121 and p1222. Throttle body looks to have already been rebuilt. And it is very clean. I'm lost at the moment.

 

A fully charged battery should have ~13.2 volts when just disconnected from the charger which should settle down and stay at ~12.7 volts some 10-15 min. later. With the lower voltage you measured, your battery might be on the way out. In any case, check the voltage on the battery while the engine (the alternator) is running. The voltage should then be ~13.5 volts. If considerably less than this, then your alternator may be faulty. If the alternator cannot maintain more than 13 V, one of the first false alarms is usually about the transmission failure like "high gearbox temperature" or "low voltage" here and there.

I suspect that the reason why you get the (probably false) "gearbox fault" only when the engine fully warms up is the cooling fans coming on and causing significant voltage drop in the system due to insufficient charge from the alternator. To verify this, connect a voltmeter to the battery and monitor the voltage from the engine start and see what happens when the cooling fans come on.

 

On cold starts, battery is reading 14.2 volts. Doesn't go below 13.5 with a warm engine and accessories on. And I doubt the failsafe and gearbox fault occur because of the fans coming. Reason I say that is because, the failsafe and gearbox fault always come on at 185 fagrenheit. Fans don't turn on until 205 Fahrenheit. Unless the AC is on. Which mine was not.

 

That's not the battery. You need to read it cold WITHOUT starting the car!