Chevrolet Repair: 92 Chev G30 transmission hard shift, vacuum leaks, coolant level

Question
Hi I have a 92 Chev G30 van the transmission started to shift hard 2 days ago also the iac is staying open creating a fast idle. I have checked vacuum lines replaced the iac motor a temp sensor as well as the throttle body base gasket, i am not getting a check engine light although it lights up at startup. Any Ideas what else to check would be appreciated thanks in advance.

Answer
Hi Brian,

The hard shift is due to the high idle.  The IAC is probably not bad, or it would have had a code.  Not a trouble light, but a code if you pulled them.  The idle is high because the computer wants it high...for some reason.  The question is WHY????

Vacuum leaks, coolant sensor good ideas.  But didn't do it.  Is the coolant level up?  Is the MAP/MAF/BAP all good?  ACT good?  Pull codes.  See what you have.  Not all sensors leave codes.  Is the timing right?  Could have jumped.  O2?  Exhaust plugged?  How about a binding cable or other linkage.  Plugged air cleaner, or air filter?

C J S