Lurked for a while, joined a couple months ago, but this is coincidentaly my first post here, I just cant figure this one out on my own. I own a 93z with its fair share of mods, but I am having a wierd idle problem. All my logging and monitoring is done through datamaster.

On a cold start it will idle at a nice ~850 rpms, and has no problem staying at its target idle rpm. I can leave it there for a long time and nothing will change, everything looks good besides the IAC hovers at 160(?). I was under the impression that it should be around 40. That is not where the problem is, though. If I blip the throttle a few times though then let it sit, the idle will start to rise on its own until it hits 1.6k in park, and there it will stay. My IAC counts drop all the way down to 0, and it stays at around 1.6k rpm in park with a target idle of 850. If it was a vacum leak, wouldnt it always idle high, and not idle perfectly on a cold start??? I have done just about everything I could think of solve this, here is what I have done so far:

- Readjusted the TPS with a DMM to read in spec(~.5v for my 93).
- Installed a brand new IAC
- Remove and dissassembled tb and cleaned everything out
- New o2s, which I needed anyway.
- Removed fuel rails and inspected injector o-rings, and spread a small amount of oil on them on the off chance one of them was leaking.
- Adjusted TB blades to full closed position
- Reset PCM to reset iac, tps %, etc.

Now common sense tells me its a vacum leak, and I suspect the rear intake smaller egr/air/whatever it is port(egr solenoid was already removed and blocked off)...but is it possible to have a vacum leak that doesnt cause any problems on a cold start???

I can attach the DM file if requested, but it has about 3 mins of useless idleing at the beginning before you can see the throttle blips and then the automatically raising idle.
Help me with this so I can go back to !

 

Pulling up on the throttle does nothing - the spring isnt sticking The blades are all the way closed, and the pcm is reading TPS% as 0 percent throttle.

Resetting the pcm makes it forget the learned tables, and the IAC position is one of them, which is relearned by either holding the gas as you start it then restarting(according to shobox), and is also told to reset by the pcm at 40mph. Neither have worked, and since its a brand new IAC i doubt it is the culprit. Nice suggestion though, it easily could have been something as simple as that escaping someone checking.

Has anyone else had a similar problem, or should I just pull the intake and check for vacum leaks?

 

TPS reads 0% and .47v when the idle goes up, while the IAC drops down to 0(fully closed, right?). This makes me suspect a vacume leak since the engine knows it is too high, and it is *trying* to bring the idle back down...but it just seems wierd that it would run fine on a cold start if it was a vacume leak, and not just always be high

 

Stock lt1 intake with the tb port matched(new gaskets on tb). Its a 93 so there is no maf.

This is frustrating, I think I am gonna pull the intake and check the passenger side egr/air/whatever it is port.