[NickCats]

Originally Posted by MNBoxster

Hi,

@ Nick - There are lots of components which do not have their own CEL. For instance take a MAF - there is no OBDII or 'P' code which states "Bad MAF". This is because the sensor either isn't self-diagnosing, or for reasons of cost, memory space, or complicated code, the DME doesn't monitor the sensor's specific condition.

Consequently, many of the CELs report a variance to known or expected voltages or conditions. Therefore, you often need to do a little detective work figuring out which components affect such conditions and using experience (we all know how susceptible the MAF is to any screwing around), intuition and deduction, zero-in on the offending component, such as in this instance.

I say it was the Evo because when it was swapped, I suspect that it either jarred the MAF into failing, or let loose some dirt from the intake tubing and set off the MAF. A MAF malfunction could manifest itself into a condition resembling a throttle body issue - Revs not matching TPS (Throttle Position Sensor), or O² Sensor data not matching expected Data (too rich/lean), etc.

This is why it isn't that unusual to see CELs when people add or disturb components which were otherwise working fine (or at least within acceptable tolerances).

I deduced that since dj reported the EVO swap, this was complicit in the issue. If he hadn't added the EVO, I suspect the car would have never thrown the code (of course, this is speculating)...

Happy Motoring!... Jim'99

Thanks, Jim !

Nick