4.3L T.B.I. Fast Idle problem.

Just purchased an older S-10 Blazer 4X4 4.3 T.B.I., 88 model that I am trying to fix up. It has an extreme high idle at start up. Ranging from 2k to 3k rpm's. It will idle down to approximately 1500 rpm's. Also the engine is harder to start after warmed up. I've tried to adjust the timing and it still didn't fix the problem.

I ran a code check and replaced the sensors it listed.
(knowingly it may have not needed this)

I have replaced the IAC valve, Throttle Position Sensor, Coolant Temp Sensor. Also I have backed off the idle adjustment screw and still it doesn't get the rpm's low enough, still 1500 rpm's.

Along with the sensor replacements I found one vacuum leak and repaired this at the Throttle Body Gasket. No help either. The Throttle Body appears not to be the original. Junk!? The Butterflies stick at the lowest OFF throttle position. And by the appearance of the unit it looks like it was setting in the floor of a garage for years before they put it on my Blazer. I am prepared to buy a new Throttle Body just because this one doesn't look like it will last, but I don't know if that will fix the problem.

I am not very familiar with the sensors and ECM units, but I do understand things like vacuum leaks and so forth. I am convinced it is vacuum and/or sensor related. Even though the T.B.I. is junk. It's out of there soon enough.

My next move is to replace the EGR valve and/or sensor along with the MAP sensor.

I would appreciate any help from anyone that has an idea on how to repair this. :Tracing the problem: Thanks.

What code no are you getting.

Thanks for the reply... As of now I'm getting Code 43.

My next thought is to replace the Knock Sensor.
Would that be your suggestion?
Honestly I have had a hard time in finding the Knock Sensor!
My repair manual isn't very clear about the location.
Is it on the passenger side below the manifold on the block?
If it is it's very hard to see.
And I am wondering about the Oxygen Sensor. Could this
be causing fast idle problems?

Since I've posted I have replaced the following:
New Throttle Body Gasket
Electronic Spark Control Module
Map Sensor
EGR Valve / Filter
Temp Sensor

I noticed a great improvement in idle smoothness after replacing
the Map Sensor and the Temp Sensor, but none of the additions
brought the idle down as I would have hoped.
Still 1400 to 1500 RPM's at the lowest.

And since my last post I have found some other problems
which may or may not be in conjunction with the idle problem.

I've noticed white smoke when I first start up with some
valve rattle. Along with water disappearing in the radiator.
I'm sure it's one of the head gaskets or an intake gasket
which I am looking further into this weekend.
Luckily I haven't found any water of any kind in the oil.
But there has been fairly heavy oil consumption since I
purchased the Blazer. I'm thinking of doing a valve job
during the head gasket replacement.

I don't think this has anything to do with the idle
but I hope you could shed some light on this as well.

I know now that I have many problems to tend to before
worrying about the idle. But that is still what I would like to
concentrate on. Thanks.

Thanks for your input and sorry for not posting sooner.
Automotive Forums has been very helpful!

Proper testing first.
Codes do not say throw parts at it.
They say chck it out.
Proper testing before throwing parts at it.
On the knock sensors check wiring real close.
Bad connectors or unplugged sensors.

Make a all data sub or a good factory repair manual your best friend.
http://www.alldata.com/products/diy/index.html

Good Repair manuals have the repair flow charts for different codes.

Take the code no and look up the repair flow chart and go threw it.
Good Luck
MT