I have a 1997 Blazer with the 4.3 V6 and an automatic transmission with 111,000 miles on it. At idle I have a rough choppy idle but once you give it gas it runs down the road great. These are the things that have been done to it - Fuel pump, Intake Gaskets, GM plugs, GM wires, GM cap and rotor, Injection spider, Fuel filter, Plentum gaskets and the carbon was removed from the throttle body and compression, vacume and fuel pressure have been tested. I have also ran all different types of injection cleaners through and also had the fuel system cleaned with a product that was introduced through the vacume system, this caused the rough idle to go away for a couple of days but now its back. Another thing that will make it idle smoother is if you let it suck about two cups of water through the vacume system with the truck at 3000 rpm, but it starts to idle rough after a few days. Random missfire code is showing up on my scanner. I am stumped and dont know what to do next PLEASE HELP any help would be appreciated. THANKS.

 

Test the Idle Air Control Valve and/or clean it. See if that helps.

 

Wouldnt that throw a code ??

 

Only if you run the engine with it off....which is a bad idea anyways. It won't throw a code though it will idle a bit high while it relearns the idle after you put it back on the throttle-body.

Make sure you pull on the valve to get in there with the sensor-safe throttle-body spray. You kinda wanna get all the carbon out. It would also be a good time to clean the area of the throttle-body that it connects to as that could be clogged as well.

Make sure you change out the base seal again when you pull the throttle-body off.

 

I will check it, but I believe I have already cleaned the IAC valve when I cleaned the throttle body and it made no difference. But I will recheck. THANKS

 

Again, make sure you replace that base seal. If your using the old one, extra air could be getting in there during idle and conditions may enhance the seal during drive apply thus tricking the truck into running better outside of idle.

 

Yes Doc I cleaned the IAC Valve when I did the throttle body, I thought I did but better to double check than to be sorry. Thanks

 

How did you check the vacuum? Leak test?

 

Yes, Leak test. The auto repair shop did it.

 

I also have cleaned the EGR valve and replaced all vacume lines if that helps. Please I need ideas, I am stumped. Thanks again