I have a weird problem... It has just started the past couple days.

When I start the truck from dead cold (sitting at work for 8hrs), it starts up fine, and runs fine for a bit. It seems to be running fine until the motor gets a little warm (not at operating temp yet). It starts to idle a little rough, nothing really noticeable though. I can drive it fine, then all of a sudden when I come to a stop, the engine surges, truck lunges forward like I just romped on the gas, and then stalls. It takes a few tries to get it started afterwards, usually a 30 sec wait and will start right up. After that it is at operating temp, and no problems what so ever... It has done this on the last 3/3 cold starts, but never when the truck is at operating temp.

I scanned the codes, none stored at all. No Check engine light, even when it surges and stalls. The light only comes on when all the other lights come on after motor is off.

I've searched for similar problems, but most have troubles when the engine is warm. I have the exact opposite... Only when it's dead cold. If it isn't completely cold, it runs fine. When warm, runs fine.

Any suggestions are welcomed and appreciated!

 

I had this problem on my 2000 S-10. Hopefully the solution on yours will be the same.

The problem on my truck was a sticking Idle Air Control valve. The IAC itself was fine, however there were some nasty gummy deposits that were causing movement issues.

When the truck was cold these deposits hardened and the IAC would stick in place. When the truck started to warm up a bit the valve would be able to move a little but not the full proper range causing a rough idle. Then once the truck was even warmer the deposits turned to a more liquid then a solid and would suddenly release and the IAC would quickly go full open causing an engine surge and a stall.

Same issue as well with the hard to start after a stall as the computer attempted to figure out exactly what position the IAC was in.

I pulled the IAC and gave it and the intake body a good cleaning and has been running perfect for the last 3 weeks.

Hopefully your problem is the same as it is an easy fix.

 

Thanks awe41... Cleaning up the IAC seemed to do the trick. I cleaned the egr as well since I had the gasket here already. Truck hasn't stalled yet, been good for about 2 days now.

Thanks again!

 

Well, after running great for the past week and a half, my wife reported it stalled out on her again. Same scenario... I'll check the IAC again, but I think it may be something else. Could TPS have anything to do with it?

Thanks.

 

96, 2-door, 4.3-W, 4 X 4, 73K. Mine surges a few times when you first start it cold-soaked, only surges 3 - 4 times, but no stall (or no codes set). After that, it purrrrrs like a kitten. I just checked with my local Chevy parts guy, the IAC is $111 wholesale. Good thing is it has an O-ring.

I have an AutoTap Diagnostic Scanner. I plan to take it out cold-soaked and record the session to see what exactly is going on with the data stream. If I find anything good, I will post it. Otherwise, I will try to clean the IAC and hope for the best.

Thanks for the tip.

 

I used the AutoTap to record about a minute of driving, that is all it took to clear the problem.

I played it back frame-by-frame. The idle speed would jump from 650ish up to 14-1900 RPM, inconjunction with the ignition timing swinging wildly between 10 degrees after to as high as 32 degrees before TDC. Then all of a sudden, it settles down and all is well... Coolant temp had only got to about 100 degrees when it started behaving. Mass airflow went to about 3.1 lbs, but I think that is in response to the higher engine speed (demand). TPS did not do anything crazy. Outside Air Temp sensor stayed at about 48 (about actual temp) the entire time.

I do not know if the IAC could cause this. Can it affect the timing control? Anything anybody knows will be greatly appeciated.

Thanks.

 

I have a very similar problem. My son actually noticed something....When the engine does this little trick...revs up high....then tries to stall, the fuel gauge was pegged WAY above full. I went inside, got my scanner to also do a live stream...but when i started the truck the fuel gauge read normal and the truck idled fine. Im starting to think I may have a bad ground or something now. Ideas?

 

I ran a live data scan. The problem has progressed. Going down the road i now lose total engine power. TPS reading goes extremely low. Sometimes zero. The truck has now thrown a MAP circuit input low code and a TPS input circuit low code. Ive checked the gounds affecting these sensors. I am questioning the 5 vdc reference voltage. I was told that the famous ignition switch problem could also cause this. I want some firm evidence before I just start throwing parts at the problem. Oh yea.....its a 97 Blazer. Have a good one!

 

I have a good relationship with a guy at the parts counter at my local Chevy dealership. He arranged for me to talk to one of their Journeyman techs.

He told me that the reason mine was not throwing a code was because the PCM is still in "open-loop." If you read up on the operating theory, you will find that there are two states - open and closed loop. It stays in open loop until every thing gets up to operating temp (primarily the cat). Then is when it goes to closed loop, and the PCM-through all the sensors does its thing, and starts setting codes when something wierd happens. He did mention that the MAP sensor could cause this, along with the Intake Air Temp sensor.

I have not noticed my fuel gauge. For now, I have just been letting it idle for about 30-45 seconds before I pull out with a cold soaked engine (probably not a bad idea anyway).

He also told me, eventually it will throw a code. You may be onto something with the MAP output low code... which usually means it stops working. I had the same thing with an O2 sensor. Also, check the connectors, unplug and plug them back in (if you have not already).

 

I have lost the 5 volt refence voltage that goes to the TPS and MAP sensor. I searched on here for the low TPS sensor input code...It turns out that this 5 volt reference is supplied to the IAT, TPS, MAP TFP and FTP sensors. If any of these short or go to ground, You will loose the 5VDC refence. As soon as i dig a tunnel in the snow so I can get under my blazer, Im going to unplug the TPS and FTP. Those are the only 2 sensors i havent visited yet. Good Luck! Let me know!