I have a 2001 Volvo S40 that has been good to me. Over the past couple of months I keep getting a check engine light with a fault code of P0101 or P0128 or both (not sure if the two together should tell me something). The car has been a little laggy unless I get on it. If I take the battery wire off for about 15 mins the car runs great for about 100 miles. I tried cleaning the MAF, replacing the thermostat, new plugs, cleaning my K & N air filter, cleaning my idle air control valve, and looked and listened for any signs of air leaks. Any help would help my stress level as I am in one of those times where everything is breaking on me all at once.

 

The P0128 for me was a bad t-stat. I'd replace it then clear the codes and see if the other code returns. If yes, then I'd clean the MAF with MAF spray cleaner (don't use a substitute), reset the code and drive it again to see if it returns again. Now if it returns again I'd bite the bullet and replace the MAF. My .02

 

I have tried the T-stat and cleaning MAF but both fault codes returned (I also tried disconnecting the battery). What would you go with next MAF or Temp sensor at T-stat, those are my thoughts but I am hoping for advice.

Inspection is in Feb so I have time on my side.

 

You cleared the codes with an OBD-2 reader and they immediately returned? If so then only the temp sensor is left. It's the sensor screwed into the t-stat housing. It's fairly easy to change for the DIY mechanic.

Personally I'd work on one issue at a time. Fix the issue with the coolant temp, then fix the MAF.

 

Thats good advice, I will just stick with the temp problem and go after that sensor. Would you stick with OEM?

 

My 2001 is too old. I just buy cheapest online if I have time to wait.