Check engine light and d4

I have 93 accord 10th anniversary addition 179k. The check engine
light came on and the D4 started blinking at the same time. Checked
the codes and came back with a 6 for the check engine light and 1 for
the D4 light. Looked up the engine light code and it says that it is
the coolent temperature switch. I cannot find what the code is for the
D4. In addition, recently the idle has been intermittenly high after
driving and then putting it into park. goes up to about 2k and
sometimes surges. Sometimes it goes back down to normal (800rpm) and
sometimes it does not. I did clean the IAC screen and checked the
coolent level. I have also searched this news group about the D4 light
but did not find any clear info. Any input would be appreciated.

 

It just means the ECU is not receiving a valid signal from the switch. This
could mean anything from broken wires to corrosion to a bad switch.

The TCM code 1 can be set by fluctuating idle.

Both these codes can be the result of low coolant. If you've checked the
coolant at the RAD and found it OK, you may have a Fast Idle Thermo Valve
that's sticking open.

With the engine fully warm and the idle cycling, remove the air cleaner
hose from the throttle body and check the LOWER port in the throttle body
with your finger. If there is suction, and the idle settles down when you
cover the port, the FITV is sticking open. This usally happens when the
cooling system has been neglected.

 

Thanks Tegger. I will check it. I recently put in one of those hi-
flow air filters which you spray oil on them to trap dirt. Maybe
sprayed too much?

 

While I despise those type of filters and recommend instant removal of them
from the vehicle, it is not likely your problem here unless excess oil is
fouling the throttle body.