S-40 problem codes
 

I have a 2000 S-40, 1.9L Turbo, automatic, with about 115,xxx miles and the check engine light on. It runs sluggish, sputters while sitting at stop lights. Plugged OBD scanner into it and this is what I got:

P0101 - Mass Air Flow System Performance
p0128 - Coolant Thermostat (Coolant temp below thermostat regulating temp)
p0171 - Fuel Trim System Lean Bank 1
p0303 - Cylinder 3 Misfire Detected
p0335 - Crankshaft Position (CKP) Sensor A circuit

Unplugged the MAF and the car ran the same. Cleaned it, but no real difference. So I need some help diagnosing what all is wrong and how to fix the problems so any knowledge is appreciated. Thanks.

First thing I would do is change the t-stat, then reset the codes and unplug the battery for about 15 minutes to reset the fuel trims. Then drive it again to see which codes return.

I would also check the fuel pressure and replace the fuel filter if it's old. Basically trying to find out if I have a fuel delivery problem or a MAF sensor problem which causes the other problems. The crank position sensor is the weird one but I have read threads where a bad coolant temp sensor caused other issues. That's why I suggested replacing the t-stat first just in case it's actually running at the wrong coolant temp and the ECM is having a hard time compensating.

Thanks a lot. I will definitely change the t-stat as soon as possible. I appreciate your help.

The car starts immediately 99% of the time. But occasionally, it takes a couple seconds longer. And EVERY time I start the car, it sputters as if it is having trouble getting gas. Do you think that is the misfire the OBD told me about or a fuel pump issue?

Again, I appreciate your help, a lot. So Thank you

That is hard to say. The S40 is not known for the fuel pump failing though. It could be something simple like the MAF is dirty or the coolant temp sensor is bad or a coil is bad. Go for the easy stuff first like cleaning the MAF with MAF spray cleaner and changing the t-stat and checking fuel pressure. Always reset the error codes after your work then drive it to see if anything changes or any codes return. If possible fix one thing at a time then test.

I had p0101 and p0171 on my 2000 s40. I replaced the MAF and the codes kept popping up. A buddy of mine is a Volvo tech and he suggested spraying break cleaning fluid along the hoses for the intake. I sprayed right on one of the valves (dealer's name - check valve) and the car almost stalled. I went to the dealer for a replacement, $40 and the light continue to come on. He suggested replacing the fuel filter and the codes are gone! You should see a smoother idle and acceleration.

A good guide on replacing the fuel filter - How do i change the fuel filter on a 2000 volvo s40 - JustAnswer

I used flat head and it worked fine.