Jut replaced the engine in my '97 626 2.0L manual. With the replacement, we changed all the filters, new plugs and wires and covered all the basics. Now I'm getting the P0300 B and P0505 error codes. The engine has trouble in the lower gears / lower rpms, meaning that it runs a little rough and you can feel the engine dragging as you accelerate. Above 3500rpm, seems to run fine reguardless of gear. With clutch disengaged, the idle will bounce from 1000 to 1500 until car is at a full stop, then it will stay at 1600rpm. So far it has never stalled on me but you can feel the lack of power when accelerating. Any ideas what the issue might be? I'm going to look at the Mass Air Flow to ensure it's clean and free of debris. Research on the internet has also mentioned the IAC Valve. Am I headed in the right direction or is there something else that I should be looking at? Thanks, Russ.

 

If it was a used engine it could be very dirty injectors as far as the midfire code. Could be alot of things but a thorough cleaning of the throttlebody/injectors/IAC/MAF would be a start. Possible vac leak etc.Techron or Seafoam in the gas tank could straighten the injectors out and decarbon the engine.

 

Thanks for the quick response. We did put Seafoam into the gas tank. I'll try cleaning as recommended and see how that works. The engine was out of a car that was totaled back in 2000. My car sat with the bad engine for about a year before I replaced it.

 

Just an update...had a few minutes so I took apart the IAC and found it to be caked in Carbon. Cleaned it out as best possible and that seems to have helped with the idle bouncing from 1000 to 1500 rpm. However, the idle will sit at 500 which is nice but too low. When driving, putting in the clutch, as the engine revs down, it will finally get too low and kill the engine.

What it does tell me is that indeed the issue is around the IAC and throttle body. I'll keep working in that area and post my findings.

Thanks,
Russ