Very rough idle?
 

Hiya guys.
Well I've seen some posts regarding a rough idle but it's always accompanied with some other issue. My blazer is a 99 4 door. 80k miles on it. New ac Delco plugs gapped at 55, New pressure regulator, new ac Delco fuel pump. On throttle it runs like a top. Smooth as can be. So long as it's moving it has zero issues whatsoever. However at idle sometimes it isn't too bad and sometimes it stumbles so badly that it dies if I don't give it throttle. Do yall have an idea on this?
Thanks

Any codes?

Did you redo the fuel pressure tests in the sticky to confirm the repair? What is the pressure when it runs like crap?

What is your system voltage at idle?

Do you have a scanner with live data capability? If so lets start with misfire counters by cylinder.


George

No sir no codes. Fuel pressure was about 50psi.giving hard stars. Replaced the pressure regulator. Didn't fix it. Replaced the fuel pump. Getting a good 70psi now. Haven't checked it since it started idling so rough.
Haven't checked the voltage with a voltmeter, battery is less than a year old as is alternator and gauge reads 15 at idle.
My code reader only shows codes for active cel lights

To explain the hard starts incase it has any relavancy, I was having to crank it for a solid 20 seconds to start. After the fuel pump it fires a max of twice before starting

OK no codes.

You should recheck fuel pressure so we don't start chasing ghosts. I don't think I have ever seen someone with 70 psi fuel pressure at the shrader after the priming cycle stops. Are you sure about this?

Its best to measure voltages with a meter but if the dash reads around 15 then your probably good.

There are many possibilities for your problem. You did not answer the question about live data capability so here is a complete guide, it works for misfires/rough idle. Let me know if you need help with any of this.

https://blazerforum.com/forum/2nd-ge...72/#post732722


George

Well I don't think my code reader has live data capability but I'll check
And I'll start going through the list in the other post. Thanks

Live data makes diagnosis much easier. We have guidance on a cost effective way to get that capability. In the meantime, that rough idle article list is pretty long. A few of the lower tech things you can check for is vacuum leaks, quality of spark and the water spray arching test.

George