I recently had my N* engine replaced in my 99 Deville with one from a 2000 deville I took the car down to get smog checked and it failed because of a DTC P0507 ( Idle RPM higher than expected) so I took it backto the place I had the engine installed and had them fix the problem they said they ran some test and the fault wasn't present so they did a complete tune-up ie.. sparkplugs, wires, air filter, injector cleaner(the expensive one) the works. drove the car for another week no trouble codes took it back to get it smogged again at the same place fault p0507 shows it face again to make a long story short took itback got it fixed cleared code drove 2 weeks took it somewhere else same code p0507 failure again!!!

My question is why does this code only come up when getting a smog test? Could it be the 2000 engine in a 99 causing problems?

 

Either you are not erasing the code or you still have an engine that is idling too fast. The idle speed can be viewed in on board diagnostics so its within spec or not.I would think the smog shop can tell the difference between a current or history code. None of the tune up related repairs address a base idle correction. Idle speed can be affected by a vacuum leak, so do a search here for vacuum leak.

 

The code is listed as history now butit wascleared the second time I took it back to the shop for repairs. that's why I drove it for 2 weeks before I had it tested again tosee if it wouldcome back. the light only comes on when i take it to get smog.

 

Are you saying on the way to the smog test, the light comes on and you still run it thru the test? In California, at least, they turn off all accessories during the test. Could the idle be affected by the climate control system being on while you drive it, then when they shut it off the idle does not correct itself?

 

No, I very seldom use the ac so I don't think it's that, the light comes on when they let the car idlewhile their performing the smog test. I had a new ECM installed when I replaced the engine do you think maybe it the new ecm causing this problem?

 

No I think its idling too fast as the code suggests. And by letting it idle you mean in park or drive?

 

In park, but I think i've narrowed it down to the Idle Air Control Valve because I believe the shop used the old IAC valve off the other engine that was replaced. Can I clean that with carb cleaner or do I just need to replace it

 

Cannt be cleaned, it will short out. Thru diagnostics it can be retracted and the idle relearned I believe. Short of that replacement once determined as faulty is the only option.