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Originally Posted by lxndr
Sorry, it's slow in the 1G CRX forum (my usual domain) but I just went through this with my ZC swap so maybe I can help.
Here is a list in order of the 8 things that are most likely to cause this problem:
1) Colgged EACV
2) Vacuum leak
3) Idle not adjusted properly
4) Bad coolant temp sensor
5) Bad MAP sensor
6) Bad EACV
7) Bad wiring to the EACV
8) Bad ECU
First try cleaning out the EACV with carb cleaner (everyone says to do this but it rarely ever works). You can take it off and clean it, or you can also clean it out by squirting carb cleaner in the hole in the TB just before the throttle plate. Make sure to do this while the motor is running and cool so the EACV is open.
Check for vacuum leaks and check that the PCV if working properly. Also check that the brass idle adjustment screw O-ring is not leaking by placing your thumb over the screw.
Check the resistance of the EACV. Disconnect the 2 pin connector on the back of the EACV and use a Ohm meter to test the EACV, it should measure between 8-15 Ohms.
If everything checks out OK, then the first thing you should replace is the coolant temp sensor. This is the sensor in the cylinder head with 2 wires coming from it (the coolant sensor with one wire goes to the temp gauge). The ECU reads the signal from this sensor and tells the EACV to close when the motor is up to temp. If the sensor is faulty it will confuse the ECU and won't let the EACV close all the way causing a surging idle.
Also, if you don't have the coolant lines running through the TB and EACV, your motor might be running cool which can also cause the EACV not to close completely. You can check to make sure the EACV is closed by unplugging the 2 pin connector. If the idle remains the same after pulling off the connector then the EACV is closed (you should hear a "Pssshht" sound when you reconnect it).
In my case the "surging idle" was caused by a combination of a bad temp sensor and a failing MAP sensor. I had tried everything else and once I replaced these sensors the motor idled perfectly.
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ill check all these tonight....thanks for the info