I finally scanned my blazer, and got DTC-35, Idle Air Control

It has been starting fine, and for a while now, when I am in park, or stopped at a light for a while, the check engine light comes on. I have holes in the exhaust and no cat from previous owner, so it's noisy and does smell like exhaust at times in the cab, so I didn't think much of it.

Now (past week or two) it's been revving quite high when it's in park. I start it up to warm it up since it's winter, and it will idle high until I get in and shift into Drive or Reverse, then the idle drops. When I shift back into park before shutting it off, it revs up then too.


Where should I start?

Blue Bowtie has a good explaination and pictures here:

http://www.automotiveforums.com/vbulletin/showthread.php?t=940598

thanks, I'll try cleaning it first and see how that goes.

cleaned it well, and it didn't change a thing, still idle's extremely high at start up.

Any good cheap place to get a new idle air control valve? or any other ideas?

You might check the wires going to the IAC for breaks or shorts first

Checked the wiring, doesn't look like any damage, breaks, burning, or anything near the unit, and the plastic wire loom is still around it and in good condition

I put a new idle air control unit on today, and it didn't really change.

Idle was high at start up til I shifted into drive. I took it for a spin, and when I stopped at a light, the CEL would still come on after sitting for like 30 seconds. When I got home I put it in park and left it for a bit. The idle went up like usual, probably around double normal idle (no tac), and it had a sputter to it while idling. I shifted back into reverse, and the idle dropped to normal, then back to park and it did the same thing.

not sure where to go from here.

You might check the "starwheel" inside the distributor. The module, with the "stars" tell the computer the engine speed, like a crankshaft position sensor on newer stuff.
If one of the "stars" is cracked or broke, the engine has to depend on the MAP sensor and TPS for engine info.

I picked up a filter for the EGR valve, and when it warms up a little outside, I'm going to pull that off and clean it and see what happens. The EGR valve has been replaced at some point (before I bought it), because it looks fairly new, so maybe this issue has happened before, i've heard its a common problem with old blazers.

I'm gonna check around a little for damaged vacuum lines too. Does anyone have a vacuum diagram or anything showing the location of all the vacuum lines?