idle problems

hey i got a 90 crx si with a z6 that came in it...i myself have not done this swap before nor did i do it in this car...but for some reason it constantly revs up and down (between about 1200 and 2500 rpms)...i am pretty much lost:banghead: and cant figure out why...ive been through a few forums on here but i couldnt really apply their problems to my own...so if anyone could help me out it would be appreciated. thanks.

ps i got a few pics of my tb setup and theres a few hoses/wires not hooked up to anything. will post if someone likes...

90 crx Si
d16z6
90 si tranny
90 si ecu
90 si harness ( i think, no vtec plugs )
vtec not hooked up

my car did that when i messed with my timing, adjust your timing to normal, then take the negative battery terminal off for a few mins to reset the ecu, worked for me

You could also pull the hazard fuse instead of erasing all of your presets and clock, just take out the fuse, the one all the way outboard in the fuse box under the hood, for 10 secs.

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.

Nice explanation man!

my friends del sol does he same thing. i asked him y the idle fluctuated. he told me he doesn't have a o2 sensor in it so maybe your o2 sensor is bad.

my friends del sol does he same thing. i asked him y the idle fluctuated. he told me he doesn't have a o2 sensor in it so maybe your o2 sensor is bad.

where does this vacuum hose go? (on back of intake manifold)
http://i29.photobucket.com/albums/c293/StreetLethal122/RIDES/CRX/DSC04674.jpg
this is what i have for intake...there is map sensor on tb and one on firewall...
http://i29.photobucket.com/albums/c293/StreetLethal122/RIDES/CRX/DSC04675.jpg
which wire do i connect to power for vtec to work?
http://i29.photobucket.com/albums/c293/StreetLethal122/RIDES/CRX/DSC04673.jpg
some more intake pics...
http://i29.photobucket.com/albums/c293/StreetLethal122/RIDES/CRX/DSC04671.jpg
http://i29.photobucket.com/albums/c293/StreetLethal122/RIDES/CRX/DSC04669.jpg
like i said before i didnt do this swap, and havent done this type before and im pretty much lost...thanks for yr help

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.
ill check all these tonight....thanks for the info