Hi everyone, I've been having some issues with my 1998 Blazer mostly with my RPM's and a bit of hesitation/backfire. With all the good information I've found around here, I figured you'd be the perfect people to ask! Recently, as in the past 3 months, I've changed my catalytic converter, spark plugs, wires, distributor cap and rotor, replaced one O2 sensor today and other small stuff such as a coolant temp sensor but it was just broke off so I don't believe that pertains to anything. I've cleaned my EGR and replaced fuel pump and filter recently as well. The problem occurs when first starting and running as well as acceleration. When started and idling, it idles rough and RPM's drop between 900 and around 600. When coming to a stop, RPM's jump from around 600 to 2,000, back and forth occasionally. When accelerating and driving, the truck lurches and spits and it sounds like my EGR isn't working right and plugging the vacuum or something but I'm not absolutely certain, but I may need a new one of those and I figured I'd as all of you and your great knowledge here first about what to do and where to start! Thank you very much for your time and consideration!

EDIT: Just for reference, the code posts are as follows:

P0152: O2 Sensor Circuit High Volts (Bank 2 Sensor 1)
P0405: EGR Flow Sensor A Circuit Low Input

 

I hope all of the replacing of components wasn't chasing after this problem.

For the book definition:
P0152 Explained
P0405 Explained

Now, if you do not have access to a Tech2 or equivalent scan tool, then much of what is stated in the diagnostic charts may be near impossible to perform.

When you cleaned your EGR valve, did you install a new gasket that had an integrated screen on the inlet port?

 

I did put a new gasket on, just not the one with the screen. And yes I do have a scan tool and I just tested again and I posted with P0152 again as well as I do believe a P0506 or 507, I do think it was the 507 though that may link to my IAC or TPS perhaps? And no, those items were mostly changed just for tune up purposes and problems in the past, I've nearly replaced everything haha.

 

P0506/P0507 Explained

That should help you out. And this code can definitely affect idle, but it doesn't necessarily point to a bad IAC valve. Run through the diagnostics as best you can and let us know the outcome.