My car is a 1990 STD hatch with a stock motor that has been converted to MPFI. Recently, 2 weeks ago, I noticed that when I am at idle my car goes putt, putt, putt occasionally. I noticed it when I was getting my mail and had the car idling. This weekend I checked the Spark plugs and they look fine with minimal black deposits on the threads. There is no smoke coming out of the exhaust and it drives just fine. I had recently found some new injectors at the wrecking yard and installed them yesterday. The car drives even smoother and it starts with 1 crank now! But, I did notice it still sputtering today when I got to work. My spark plugs are 2 months old, my spark plug wires and fuel filter are about 2 years old, my fuel pressure regulator and IACV about a year old and very clean still, and my idle is right at 750 rpms at idle. I also checked the timing yesterday and it was on point. I did notice that my oil level was at the middle of the dip stick so it may be burning some oil, I last changed my oil 3 months ago. Any ideas of what could be causing the sputtering?