Ok my 2000 blazer won't idle. Once I start the engine I have to keep my foot on the brake while keeping my other foot on the gas keeping it at 1on the rpm gauge. As long as I do this it will stay running. Once I'm driving it runs great to missing after she warms up. I can drive across town and she drives great till you come to a stop. That's when you have to hold the brake while sitting at the red light with foot on the gas at 1 on the rpm gauge. She will stay running long as you do that. What can it be? Also I'm not sure if this helps diagnosis the problem but my ac also runs hot like no freon but it will get cold as hell sometime then changes to hot air as fast as it was cold. Sometimes it stays cold 20 min sometimes it switches back an forth every few minutes. Any help appreciated.

 

the issue with the AC is the compressor is cycling on/then off. If there is no freon, the compressor will never run and only blows hot air. Its outside/engine heat blowing through. The two issues would be either electrical or over/under charged with freon. I would not think it is a charging issue since it is erratic. But the best way for charging is to recover oil/freon, vacuum it down, check it if holds vacuum, then recharge to the correct lbs. As far as the performance issue, what tune ups have you done with it? the basics? if you have not done anything or if its been "too long", the first place to start would be a tune up. After that, everyone can start to rule out different things. Not telling you to go spend hundreds and throwing parts at it, only tune up that has not been done past the recommended time/milage. Alot of issues are solved just by doing basics. A prime example would be my sisters kia will not start up if it starts to get low on oil. Someone, Im sure, has beat their head on the wall because it wouldnt start.

 

I have tuned the blazer about 8 months ago and new wires. They also did all service to it. Like I said after it gets going you wouldn't even know there's a problem it's just when taking off and slowing down to a stop.

 

No mention about auto or manual tranny. When warm, what is the RPM's at idle without any assistance from your right pedal? With auto, idle speed when warm and in gear should be 575 RPM's.

I'd start with the IAC valve and its wiring to ensure it is working correctly, then I'd look for a vacuum leak in the power brake servo either clamp off the vac line to the servo or hook up a vac line to the intake manifold. 3d place I'd look was to see if somebody messed with the idle speed adjustment on the throttle body ( a no-no if the IAC is working correctly.) A Code reader that is capable of reading IAC steps from the OBDII port would tell you if it thinks it is fully open (more steps = more open) mine reads about 25 +/- 5 steps at idle and in gear but stopped.

 

Lol, mine just started the exact same thing. I was think crank position sensor or EGR.

This only happening for you in neutral or Drive as well? In park it's fine. Also sometimes doesn't do it and everything runs fine.

 

Ok, I replaced the IAC valve and throttle position sensor while I was at it. The IAC valve was the issue. Or maybe the Throttle position, but I doubt it was that one.