: po 300, po 507 need help asap!!

03-08-12, 11:33 PM
I have a 2000 deville with 190,000 miles it started idling really low and died a few times and set a code for low idle speed and code for maf/map sensor I replaced the map sensor, cleaned the maf sensor and throttle body, put in fuel injector cleaner (mixed way too strong at first but when I realized how much I put in I drove to the gas station and diluted it to proper mixture with a full tank of 85 octane, used 85 non ethanol instead of the 88 i usually use after being told how bad the 88 with ethanol was after driving it mixed too strong for about 20-30 miles) also replaced plenum and intake gaskets which didn't appear to be bad. Long story short none of those were the problem the problem was the little plastic housing under the pintle on the IAC was broken off and preventing the pintle from going all the way back in and idling up the engine, I never replaced the IAC just removed the broken piece. It ran perfectly for just a few miles, now all of a sudden has a po300 code and a code for high idle po507. Could it be the low octane gas, plugged fuel filter after using cleaner, something with the IAC not working correctly, or I also noticed the EVAP solenoid connector was damaged when I removed it and most likely not making a good connection (It never has or is now setting any code for evap system) I pinched off the evap hose and it didn't change the misfire at all, could the evap solenoid not getting a good connection to open and close cause the po300 misfire problem. I know it could be the coils, plugs etc. but before I investigate those I want to make sure it couldn't be anything I caused since it started very shortly after the other repairs I did.

03-09-12, 10:00 AM
The IAC valve is sealed with an o ring on the housing. Is the o ring seal still intact? Perhaps that is the source of your vacuum leak?