IAC for '90 5mt

[Lunatech]

Ok...the other day, I started my car like normal and instead of the revs holding around
1.5 K or so like normal for the first minute of startup, they immediately dropped straight to ~400 rpm as the engine sputtered and died. I restarted it, and held the revs at ~1K manually for about 5 minutes, then it settled to normal idle of 750 rpm. ??? After cleaning it and having no change, I couldn't find any procedure for checking the old style IAC, so I put a meter on the 2 contacts and it had 100% continuity. I uncrimped the housing and unwound the coiling of the solenoid, slowly. I unwound about a foot at a time and kept checking the ohms with the meter. A few feet in I started getting 10 ohms of resistance, so I started winding it back up, soldered the two ends back together, reinstalled the solenoid back into the housing and put the whole thing back together. I then started the car and it worked perfect...for about ten minutes. Than went back to not working. I then shut it down, checked the resistance, still at 10 ohms, checked the voltage at the plug, still 12 vdc. Pulled the solenoid off plugged it into the harness then had the wife turn the key on and it pulls the plunger in.

Is 10 ohms enough resistance for it to work properly?


Can anyone confirm what it should read (ohms wise) or have a '90 or '91 MT that has a working solenoid type IAC? If you do could you please take a resistance reading and report back to me what your ohms readings are?

[Lunatech]

How big of a PITA would it be to switch to a newer IAC, say one from a '92 4eat car?Are we talking manifold, harness and ECU, or is it simpler than that?

[Legacy777]

The wiring is different, as there are two wires and a ground going to the IAC valve with the newer valves. So that would really be the biggest thing I could think of. Swapping the ECU shouldn't be a big deal. You'd also have to swap MAF sensors.

[beatersubi]

^Correct.
I just went through this w/ my '91.
The IAC must match the ECU to work properly. But the 92'+style will bolt on to the manifold, no problem.
I can take a ohm/resistance reading in the morn, if you're still interested. Which pins did you read?

[Lunatech]

My IAC has only two pins, the harness has three wires but the center one is not used. As such I just unplugged the harness form the IAC and put one lead on each pin of the IAC.

[beatersubi]

I'll have to look at mine again. I was sure it had three pins. I know the harness has three wires. You sure the middle wire isn't supposed to be the ground?
Also, you still interested in a resistance measurement?

[Lunatech]

Yes, still interested in the resistance reading. Did you swap the IAC on your '91 and is it a manual trans?

[Legacy777]

If your harness has three pins and two of the pins go back to the ECU, then yes I don't see any reason you couldn't swap IAC valves.

Hmmm....just looked at the wiring diagram, and all I really think you need to verify is whether you have 12v on that middle pin with the key in the ON position. If so, you could swap the valves, MAF, and ECU. I'd definitely recommend using a 90-91 AT JECS ECU. The 92-94 injectors were a little different, and will cause some issues with fueling if you decide to use a 92-94 ECU and keep the 90 injectors.

http://www.main.experiencetherave.com/s ... C_diag.jpg