Hello everyone I just joined the forum today. I was looking for help with my 94 silverado 4.3. My idle is having major problems. It sits at about 800 rpms in park and the minute I put it in gear or turn the ac on the idle drops to about 400 and bounces erratically between 400-800. When im stopped at a light the truck is fighting to stay on. I've replaces tps map iac fuel pressure regulator cleaned the entire tbi with new gaskets, checked for vacuum leaks and still cannot seem to find the problem. Spark plugs cap and rotor were done a couple months back. Any ideas what to look at next? Thanks anythinges helps

 

I'd recommend revisiting vacuum leak.

 

Okay i will look into that again. Anything I should check besides around the tbi and all the vac lines? I've tried spraying carb cleaner.. almost a whole bottle and the propane method but don't notice the idle go up at all. I forgot to add, the rpms will not increase like they are supposed to with the ac engaged. It only drops. I noticed a noise from the muffler. Could an exhaust leak cause this maybe?

 

Might be a plugged cat.

 

Is the check engine light on?

 

The cat is fairly new, I couldn't imagine it was clogged. I was getting a code 35 it stayed on before I replaced the iac and now it just comes on when the truck is running rough

 

It had the exact same issues with the old iac?

 

It's a new iac. Thats why im so confused. Everything is pointing at iac. Like how it doesn't kick the idle up with the ac on. But it's brand new. What are the chances it's a bad iac?

 

Understand, even new does NOT mean it is good.

 

That's what I was wondering. Its lifetime warranty I'll have to take it back. I'll post my results once I get to that