QuestionQUESTION: I have a 1992 Blazer 350 auto that stalls at a light or to a s when slowing down to a stop. Idle air, temp switch, pickup coil, dist module, ecm,all replaced, vacuum lines that I can see have been checked egr seems to be working fine. I thought I may have a problem with ground, It seems to discharge a lot with foot on the brake, or turn signals on but may be sensitive guage, have renewed all grounds and replaced alt. Could it be a ruptured brake booster although it stops fine? Starts up immediately after stall so don't think its is fuel, runs fine otherwise. I know of another 1500 truck that does the same. He hasn't done anything to his waiting for me to fix mine and I'm loosing patience!
ANSWER: You seem to have covered most of the basic items already.
I would like to know if the vehicle stalls every time or just once in a while?
If the brake booster is defective or leaking you should hear a hissing noise.
Are there any codes?
There has been some problems with the throttle body plates sticking and binding or having excessive play which may let more are in the engine bypassing the IAC. Check your IAC counts at idle in gear. If they are at zero or very low you may have defective throttle plates.
Or the throttle body gasket may be leaking. Spray carb clean around the throttle body base to check for leaks.
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QUESTION: It stalls 99% of the time, I drive it with foot on the throttle, keeping the idle speed up so i don't notice it , it sets no codes, Yes I did notice the throttle plates sticking, but I thought it was idle adjustment was set too low. How do you check the iac counts? Thanks for the quick answer.
ANSWER: You should usually never adjust the idle on the throttle body. Actually it's not an idle adjustment it's calibration to get the proper air flow rate past the throttle plates at closed throttle position.
Did you adjust that adjustment?
If yes, that could be your problem. You may be bypaasing the IAC and causing it zero out.
Do you have a scanner or can you borrow one?
Also where do you live...alltitude?
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QUESTION: Yes I did adjust that screw, ha it is usually sealed and I thought wow , someone didn't do this right, but any way yes I adjusted it, seems the plates were hanging at closed throttle and the idle seemed too low, by ear,. Yes I can get a scanner, and I live in Virginia.
AnswerThe IAC valve controls the idle of the engine, not that adjustment.
Here is what I would start with:
Get the engine fully warmed up. Plug a scanner into the Data Link Connector under the dash. Program scanner to scan live data or data. Look for IAC counts. With the engine idling in drive the IAC counts should be between 9 & 20. If it's not in that range, adjust the throttle body screw as follows.
If the IAC counts are lower than 9.- slowly (about a quarter turn at a time then wait a minute) TB screw as if you were lowering the idle. Keep lowering idle screw a quarter turn at time, then wait a minute until the IAC counts are over 10. If the IAC counts are lower than 9 and will not go higher after adjustment you may have a vacuum leak causing this.
If the IAC counts are higher than 9 to 20 then turn idle screw the other way until proper iac counts are displayed.
This will put the throttle plates in the proper position for the IAC to operate properly. What I think is happening is the throttle plates are open too much causing the IAC to bottom out a zero counts. Then when you need a little more air flow like coming to a stop the IAC is so far out of position it cannot compensate.
Remember as stated before, sticking throttle plates will do this too.
