I have an 89 460 EFI. I'm getting an error code 12 from the EEC-IV KOER test. This code means: "Cannot control RPM during ER Self-Test high RPM check". I thought maybe it's the IAC that is bad, I removed from engine and cleaned it, let it dry, with no change. I tested the resistance and it was 10 ohms (within limits of 7 -13 ohms). If I disconnect the IAC plug, the rpms drop a little, but the engine keeps running, isn't it suppose to die? I can also feel a little bit of suction from the IAC even when it's electrically disconnected.

Also, I have noticed that if I plug with my hand the throttle body openings, the engine will immediately die (while the IAC is still electrically disconnected), so I'm guessing I have no vaccum leaks elsewhere. I also noticed that the TB butterflies let in quite a bit of air, are they supposed to fully seal and not let air in at idle?

Thanks for any help.

 

The butterflys let a certain amount of air in at all times for the enigne to idle. Check pin continuity because if a pin isn't touching or berely touching the information going to the computer cant not read correctly and will not keep the engine running where its supposed to. That running while you unplugged the connector gets me thinking though. Maybe theres a default mode if something happens I dont know. I assume there is something faulty in the IAC itself so Just replace that and see what happens.

 

Actually on most EFI motors the is an rpm spec for the IAC disconnected. Usually around 400 to 450 rpm.

 

Thank you for the replies. The EGR is physically plugged on the motor, but I have the EGR eliminator electrical plug on order. Today, I just made one myself with 2 resistors (235 ohms and 2.35K ohms) so that the voltage from the EGR wire to the SIG RTN on the EVP plug was about 0.5 Volts. Check engine light has gone off, code 31 is gone, but code 12 is still present, what I think is happening is that when the engine is performing KOER test, it will open the EGR valve to get more air and increase idle, but because the EGR valve is not opening that is why the code is still there. I also have codes 82 and 85 on KOEO. I also noticed that the engine is less sluggish and re-gaining some more power, this is what got me investigating in the first place. But, on hard acceleration, it sounds like it's not getting enough fuel, fuel pressure tests were good, (32 psi at idle and between 30 to 36 PSI with throttle). The motor is now only running on the high pressure pump with a fuel cell above engine level, I wonder if the lack of the secondary low pressure pump is starving the engine on acceleration...