IAC recal on '92 without Tech1?

[crazyd]

Hey all,

I've got a '92 DOHC/5-speed with an ongoing problem that I think is IAC related. When I reset the ECM, the car drives beautifully. But as the miles rack up and the computer thinks it is dialing itself in, drivability starts to deteriorate and it develops some jerkiness. Like it lets out a jerk when I let off the gas, or the revs fall off too fast and shifts are rougher than they should be.

Now I've been troubleshooting this from a lot of different angles for several years, particularly on the fuel and vacuum side and I've ruled those out. So often I've had more pressing problems to solve with it that a minor drivability issue like this is pretty far down on the list. But today it was especially badly behaved, and got me thinking about the IAC follower in the programming. Even though I've replaced the IAC a couple times on it, it might need calibration so the follower reacts properly. I have the GM service manual, and it says that the IAC has to be recalibrated with a Tech1. Has anyone figured out how to do it WITHOUT a Tech1?

[robertisaar]

all it's refering to is the idle-learn procedure, which more or less commands the engine speed to ~1000RPM while tracking the IAC steps necessary to keep it there until it reaches a certain coolant temp.

possible to do without a tech1, but i don't have the information necessary to build mode4 commands on $DF cars.

[crazyd]

Does that mean that building mode4 commands is a necessary prerequisite to performing this without a Tech1, or is there another way?

[robertisaar]

well, you would need to use mode4 commands to tell the ECM to idle at 1000RPM for whatever the duration of the test is.

[walterdude]

http://60degreev6.com/forum/showthread.php/46830-car-went-toyota-on-me?p=426379&highlight=#post426379

I "THINK" this may help out.. It's how to do an idle relearn, which will reset the IAC.. It also tells how to fine tune the IAC..
Hopefully this will help,,,
Tom...

[crazyd]

Interesting, I hadn't seen that page in the manual before. I'll try disconnecting the IAC and see if it stops, I didn't know you could do that for a diagnostic(whereas disconnecting other stuff often makes things worse).

[crazyd]

Just took it out for a drive. Let it warm up first, then it started acting up before I got out of my neighborhood. Disconnected the IAC, drove off and it drove perfectly, all drivability issues gone. So is this more likely a bad IAC, or just a calibration problem?

[crazyd]

Took out the IAC and checked the pintle, no buildup there and it looks clean overall. I have another one from a junkyard car I collected, but I don't think it will make a difference as I've tried swapping them before.