I have 03 Blazer with 99,000 miles and I have had it for a little over year. About a month ago it started running like crap. It developed a rough idle and a surging problem.

When I stop at a light or a stop sign the rpm's hang at 1000 and take about 5 seconds to drop to 600 and then it jumps up to 800 and bounces back and for. Now it gets worse if I'm sitting in traffic with my foot off the gas it slowly accelerates on its own.

So I cleaned the MAF, TBI, IAC and sea foamed the engine. Still the same results so I replaced some of the vacuum lines that were in bad shape and checked the fuel filter and it had no problem pumping gas out of it. Still no change in how it runs.

I have pop-up which I took out for the last time last weekend and usually have no problems pulling it but last weekend I had a hard time getting up to speed on the freeway.

So I stopped at my buddy’s house when I got home so we could throw it on the computer and check it out. There where no codes so we started checking the fuel pressure with the key on it was at 56 psi. We then kicked on the pump with the scan tool it went from 56 to 58 and then dropped to 52 and came to rest again 56. We let it sit for awhile and it stayed at 56.

I did replace the fuel pump less than a year ago so we where thinking that it went bad again but haven't had the time to drop the tank to check it oi was getting ready to go on a unplanned road trip and as I was backing out of the driveway I the SEL light came on and when I pulled the code with a code reader it came up with P0452.

So my question as I get ready to drop the tank and do a little trouble shooting this weekend can the fuel pressure sensor cause those issues or am looking more at bad fuel pump? (It is not a ac delco unit unfortunately I had to go price I think it was a spectra premium pump.)

Any thoughts or certain things that I should look for?

Thanks

 

Open the throttle body up and look down in the intake plenum for clean spots. Could be a leaky fuel spider causing the rough running, and the surging. The fuel pressure seems a bit low so it could be filter/pump as well but if the fuel spider hasn't ever been worked on that's also a possibility.

 

I looked at that when I cleaned the TBI and there where no clean spots thats for sure.

 

I just started having that same problem today. I noticed that when I paid the toll to cross the bridge, I was idling at the 15mph speed limit. On my way home, down the off ramp, I had to have a heavy foot on the brake to stay stopped (it's downhill and rainy). Then I realized it wouldn't be so difficult if it was in neutral. So I put it in neutral and the idle jumped up to 1200 then dropped down to 800 slowly.

Here's what's happened in the past 4 yrs:

2007 - replaced fuel pressure regulator
2008 - replaced fuel pump assembly
2009 - replaced fuel pump and fuel filter
early 2011 - paid someone to replace fuel pump assembly

Right now I'm getting the following codes:
P0304
P0440
P0452

Can anybody point me in the right direction? I need to pass emissions by the end of the month.

 

Still haven't solved my problems but I did replace my vacuum lines and put in a check valve and that seemed to help. Now the surging isn't as bad but mpg's suck. I was getting around 18-20 mostly highway not I'm lucky to get 16 and put on about 400-500 miles a week. I also changed the fuel filter at the same time. I need to check my fuel pressure again and see where it is at because my one year warrenty on my fuel pump is almost up.

Let me know if you figure out your issues this thing is driving me nuts.

 

Have you replaced your o2 sensors?