I have a 98 Chevy Blazer, 4.3l, 155000 miles on it. It was stumbling (not all the time but most of the time) between the 2000-2500 RPM range. Other than that it ran fine at take off and cruising. I cleaned the IAC valve, EGR valve, and MAF sensor. The IAC and EGR were horrible, :-(. MAF seemed ok but cleaned it anyway.

NOW, my idle is really low (400-600) and engine chugs and stumbles at take off, but runs fine through out the RPM's........ Now it is throwing P0171 and P0174 codes :-(

So I fixed my mid RPM stumble and created a idle, take off stumble.

I have read it may be the PCV valve. That is new within 2 months. MAF sensor is going bad, but I think my readings seemed to be normal from what I have searched on here. Others suggested to check fuel pressure. I can't do that tonight, it will have to be Thursday. But, I can recheck the PCV valve in case I did crack it or something.

So, my questions is, did I clean the EGR, MAF and IAC too much, not enough? Should I re clean them again? I know the EGR and IAC were really bad, is there a trick or something I missed with those. I used a tooth brush and throttle body cleaner on them.

Thanks

 

The EGR valve, and the Idle Air Controller, are very fragile. If you manually move the pintles off of their seats to clean them, the component can be permanently damaged. If they are damaged, they will set DTC's in memory, and illuminate the service engine soon light.

P0171 and P0174 means that both upstream oxygen sensors are reporting a lean fuel mixture. Both DTC's need to be properly diagnosed, it doesn't necessarily mean the sensors are bad. When an oxygen sensors reaction time slows down, or the sensor fails completely, it will report a lean fuel mixture. The mixture needs to be artificially enriched to see if the sensors can detect it. In other words, we need to know if the mixture is in fact lean. There are several things that will cause a lean mixture, most commonly a vacuum leak, or low fuel pressure and or volume. If both DTC's appeared simultaneously, it's extremely doubtful that both sensors failed at the same time, so checking the fuel delivery system should be the first thing on the list. It's free, easy, and doesn't take long to do it. This link explains: https://blazerforum.com/forum/2nd-ge...eakdown-88305/ Post all 4 readings, and we can analyze them.

 

Thanks
I will try Thursday night if not this weekend. I just didn't know if I should recheck something out or not :-)