Guys, I spent a couple of hours reading the threads about high idles before I decided to post this. Using that information I pulled the intake tube off the TB and did the cover the IAC port test. The engine immediately stalled when I covered the port so I think I am okay with "no" vacuum leaks. It is 3.4 with no mods.
Here is what it does. It starts at about 1600 rpms and then starts to climb as it warms up. It goes up to around 2000-2200 rpms from there. It runs fine with the exception of the high idle. Before doing the IAC test above I looked around for cracked lines or other obvious stuff and didn't find anything. I pulled the codes and found nothing but the normal 1-2. I think my IAC has crapped out. Does that sound reasonable?

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Could very well be. Before replacing it, I'd first pull the codes if there are any.
Then pull the ecm fuse for a few minutes to reset the ecm and take the car for a drive .
See what your idle does after that. If it does not settle down then you might think about changing the iac.

did you check the egr tube for cracks

You may want to consider cleaning the IAC, carbon gunk will build up on the tip.
Spray some throttle body cleaner in the IAC air path to clean out any build up.
Check that elec. connector is clean and corrosion free. Use care when removing the connector, the plastic can crack.

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88 Stock GT
I'm not cheap, just fiscally responsible

I checked the codes and it shows none. I think I will try restting the computer first. If that doesn't work I will take the IAC out and check the adjustment. I also have an old one to swap in as a test. The EGR tube is pretty new and I can see no sign of cracks. Like I said the engine stalls with the IAC port test so I believe I don't have any Vacuum leaks.

Have you driven the car yet? When you clean or replace the IAC it will normally have a high idle. You need to drive the car over 40mph for the ECM to reset the IAC. If you clean the IAC then drive it and the idle doesn't come down, Then the IAC is bad.

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Happiness isn't around the corner...
Happiness IS the corner.
ZZ4 Powered !!

couple of interesting checks from the fsm:
for code35, but the info is relevant and also a good test:
from step 3:
If idle is too high, stop engine. Ignition on. Ground diagnostic terminal. Wait a few seconds for IAC to seat ,then disconnect IAC.
Start engine. If idle speed is above 800rpm +- 50, locate and correct vacuum leak.

to check IAC windings: pins a/b and c/d are the pairs, should be more than 20 ohms for eahc pair, they don;t give a spec for the highest, but an open is bad.

to check the ecm drive lines, disconnect iac connector, at harness end, use test light, ignition on, diagnostic pins shorted, check eadh terminal to ground, they should all flash. ( this is because it is trying to seat the connector, it will just keep going) if all are flashing, that is good.
You can verify the mechanics with a helper, but be careful you don;t launch the pintle on the IAC:
remove the iac, screww the pintle all the way in. with it connected to harness, hold the unit with finger pushing against the pintle to hold it in to the IAC, have helper turn ignition on, and short the diagnostic pins (a nd b on the aldl connector). you should geel the iac driving the pintle out. without your finger on it, it will end up somewhere you will never find it, so be careful!!!

Actually that last test will check everything easily, may want to start there....

quote Originally posted by tjm4fun: couple of interesting checks from the fsm: for code35, but the info is relevant and also a good test: from step 3: If idle is too high, stop engine. Ignition on. Ground diagnostic terminal. Wait a few seconds for IAC to seat ,then disconnect IAC. Start engine. If idle speed is above 800rpm +- 50, locate and correct vacuum leak. to check IAC windings: pins a/b and c/d are the pairs, should be more than 20 ohms for eahc pair, they don;t give a spec for the highest, but an open is bad. to check the ecm drive lines, disconnect iac connector, at harness end, use test light, ignition on, diagnostic pins shorted, check eadh terminal to ground, they should all flash. ( this is because it is trying to seat the connector, it will just keep going) if all are flashing, that is good. You can verify the mechanics with a helper, but be careful you don;t launch the pintle on the IAC: remove the iac, screww the pintle all the way in. with it connected to harness, hold the unit with finger pushing against the pintle to hold it in to the IAC, have helper turn ignition on, and short the diagnostic pins (a nd b on the aldl connector). you should geel the iac driving the pintle out. without your finger on it, it will end up somewhere you will never find it, so be careful!!! Actually that last test will check everything easily, may want to start there....

In addtion to the above, I have someone start the engine while I use my finger to simulate the pintle in the TB and you can run the IAC in and out as needed by varying the engine speed. (as long as the iac is working)

Cracked EGR tube was the cause last time I had this problem.

I disconnected the battery to reset the computer and that seems to have done it. Just before this started I had driven a while with a loose vacuum line. I think the IAC got stuck trying to compensate for it. THnaks for all the help everyone. I love this place.