New to 24/7... having P5 issues...

Hello Everyone!

I have a 2003 MP5 that has been having issues. A couple months ago I had two codes appear (P0171, P0090), Fuel/Air ratio too lean and Fuel Pressure Regulator. I saw some reports of it happening with just some bad fuel. So I cleared it and waited for it to come back. It never did until this week.
This week the same two codes came back. I ordered a new Fuel Pressure Regulator, hoping that this would solve both issues. Before I could go to the parts store this morning, my wife took the car out. On her way home while driving on the freeway, the car started to buck and drop RPM really quick and the check engine light came on. She nursed it home and I took it around the block to see if I could get it to recreate it. I got it to happen in gears 1-3 (it happened to her in all gears). I checked the codes and got three this time (P0340, P0090, P0300), Camshaft Position Sensor Circuit Malfunction, Fuel Pressure Regulator, and Random Cylinder Misfire. I read that the P0340 could be caused by a weak battery and noticed our terminals were a little corroded. So I thought that could have been the cause.
I borrowed a friends car and went to pick up the part and some battery cleaner. After cleaning the battery and replacing the Fuel Pressure Regulator, I took it for a spin. Everything appeared to be fixed. No surging or jumping during acceleration. I did some stop and go, then tested freeway speed. All seemed normal.
Later today after driving for about almost two hours on the freeway, we got off on to residential streets. Within the 5 min from the freeway to our house, it did the same jump/buck thing three or four times. But now it does it once and its done for a bit. Whereas before it would almost constantly do it. Still in different gears at different RPM, but always while accelerating. No codes are currently being thrown, not even pending codes.
Any ideas what this could be? I'm thinking it still has something to do with the fuel line. But I really have no idea. Any thoughts or ideas would be of great help. Thanks!

0300: might as well replace the spark plus, coil packs, and spark plug wires if its been awhile.

clean the mass air flow sensor as well as what was suggested above (there is a special cleaner at the parts store, dont use just any cleaner as the sensor could be damaged) its the sensor right near the air filter box in the intake tube(if your unsure which one it is) cleaning the maf may clear the issue and cannot hurt even if thats not the source of your issue. i clean mine every few oil changes along with the throttlebody and idle air control valve. pull your plugs and check if they are oil covered or wet (if clear and wet then they may need to be changed do to fuel pressure regulator fault causing excessive fuel use)

Thanks for the ideas! I cleaned the MAF sensor a couple months ago, but I could do it again. I will probably be replacing the plugs, coils, and wires just to be sure there isnt an issue with them. The car has 107K miles, so it could need it.

Update: Started doing it again today after about 30 min of around town driving. I payed attention a little more. It seems like while accelerating, it drops 4-500 RPM instantly, then catches and jerks back to what it should be. So that no longer sounds like a problem in the fuel line to me. Maybe that Camshaft Sensor code wasn't caused by the corroded battery terminals? Also, just before I got home, the check engine light came back on (finally! tell me whats wrong!). But it gave me the original 2 codes: P0171 Fuel/Air ratio too lean, P0090 Fuel Pressure Regulator. 0090 Makes no sense, I replaced it yesterday and its kind of a hard one to screw up... I'm thinking I'll double check for vacuum leaks then go pick up an O2 sensor for the P0171.

Any more ideas?

unplug the coils and wires one by one while idling to see if a coil has failed. then pull the plugs and check for fuel or oil contamination while your in there checking for vacuum leaks

^^ thanks for the tip! Ill make sure to do that.

I dont think you're getting enough fuel. P0171 can either mean that you're getting too much air or that you're getting too little fuel. P0090 with a new FPR might mean that your not getting enough fuel to regulate. My guess is fuel filter or pump.

Check your PRC solenoid too. I'd actually do this first.

I found the cause of the jolting engine. I had my timing belt replaced a little while ago. The genius mechanics routed a wire leading to the spark plugs, right past the A/C belt. So the belt cut into the wire a bit, the the exposed copper would contact the mount holding the A/C and make the engine jolt. The wire has been repaired, and so far no more issues.

As for the P0171, I found a his from the top/back of the engine. We cant find any hose that is leaking, and it is a REALLY loud hiss. So we are thinking that it could be a Intake Manifold Gasket that broke and is letting air in. We plan to take it apart and put a new gasket in. And of course, check all our hoses on the way

Spark88 said:

I found the cause of the jolting engine. I had my timing belt replaced a little while ago. The genius mechanics routed a wire leading to the spark plugs, right past the A/C belt. So the belt cut into the wire a bit, the the exposed copper would contact the mount holding the A/C and make the engine jolt. The wire has been repaired, and so far no more issues.

As for the P0171, I found a his from the top/back of the engine. We cant find any hose that is leaking, and it is a REALLY loud hiss. So we are thinking that it could be a Intake Manifold Gasket that broke and is letting air in. We plan to take it apart and put a new gasket in. And of course, check all our hoses on the way

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Good find, thats why i like doing my own work

Spray some carb cleaner or starting fluid around the intake gaskets and hoses, when revs go up, you have found your culprit.