djtech

...Because apparently this little sucker that controls a choke looking plate inside my throttle body on my '90 Civic is not working at all...I tested to see if there was voltage going to the solenoid that actuates it but there was none at any RPM...I cannot seem to find why there is none either...There is no error code...Anyhow I manually hooked up a separate vacuum line to the Tandem Control Valve and viola, it opened the plate completely full and instantly fixed my power/acceleration problems...Now my question is, why did that have such an effect and how can I somehow get that solenoid power to get vacuum to the valve...Can I just run a vacuum hose to it at all times and keep it wide open? Or is there a way I could rig it to some other circuit that would turn on the solenoid to let vacuum through if the temp of the engine hit normal temperature? I say this only because it doesnt run too well when it is cold with that valve on.

Thanks for any help!
Deej

StorminMatt

First off, there is no error code for the tandem valve. So even if it is disconnected, you will never see a check engine light. As for why it isn't working, first check the wiring between the ECU and solenoid plug (orange wire). If there is no continuity, this is your problem. Secondly, check for power at the black/yellow wire. There should be 12 volts when the key is on. If not, find the break or blown fuse. If both these prove to be fine, try another ECU. DPFI ECUs are a dime a dozen used these days. So it won't set you back too much.

djtech

Hey thanks for the reply so fast...I actually have the Honda Service Manual for my civic and followed the diagnostic on the Tandem Valve...It basically said what you said...I never saw any voltage on those two wires...No matter if the engine was hot/cold or if the RPMs were at idle or 3000...Therefore I figured something was wrong...And I noticed that plate never opened up as it should...What is the orange wire for? Is that ground? and the Black/Yellow I presumed was + and I hooked the negative lead to ground to test...I checked fuse 14 as it stated but it was not blown either....How much do 1990 DPFI ECU's cost anyhow...Can you trade them in?

B16CRXT

Back from the dead. For some reason, I can't find info on this part in my Honda Shop Manual...

I just want to know more about it's function. It isn't even offered on Majestic Honda anymore. This leads me to believe it isnt a very critical component. They still sell the dashpot diaphragm.

I'm trying to sort out a couple problems with a couple different dpfi civics. One is really jerky when letting off the gas, which could be the dashpot from what I'm read online. Is this accurate? My shop manual only details how to test the stupid thing in the idle control section.

The other has a high idle that surges when dropped to normal....unplugging the eacv when it is high drops the idle but causes a surge...

B16CRXT

turns out the jerking was because the EACV was not wired up. I had to run wires from the sensor to the ecu to fix this because the originals broke somewhere down the line. This also corrected the surging idle.
I do still have a problem with cold start idle though. I have to hold the throttle to get it to idle for a few seconds before it will do it on its own when cold. Could the tandem valve be the cause of this? What would happen if I zip tied this wide-open? Could it cause any trouble? TIA.

Ken Knowles

I zipped tied mine wide open about a year ago. I have been through 3 O2 sensors. I am wondering if the zip tie is causing the O2 to fail.