Hello, long time lurker, first time poster.

My gf has a 2003 SS Pace Car (150K) that has an issue with a hesitation/stumble etc when going uphill. It also surges when floored above 3500~4000 rpm. I pulls all the way to redline, but you can watch the tach flatten out momentarily after 3500-ish on its way to redline. I have OBDCOM laptop software, but that hasn't revealed anything substantial, I'm thinking a drive while plugged in is in order.

What I have replaced chasing this gripe:
MAF sensor (someone broke it leaning on the engine)
plugs
cat delete with O2 emulator
fuel filter (this helped greatly, but the surge/hesitation is still there)

Prior to these repairs, 85 was about all the Pace Car was good for. After changing the fuel filter (last part changed), I lifted at 105. So it would seem that I am going in the right direction.

 

I should also mention that if I slip it into 3rd gear that it goes up the hills just fine.

 

Hmmm, that is a hard one. My guess would be maybe check the air filter? I know it sounds simple but if something is stuck in it, can cause insufficient air flow into the engine at higher RPM. Also make sure it is the right one. It almost sounds like something electrical, or something to do with the EVAP system.

Also as far as the the max for MPH is 112. I put mine on a dynamometer and it would only let me go to 112 mph.

 

Thanks for the input, the car also has a K&N filter element, but I was considering taking a look and clening everything from the air box to the throttle body.

My OBDCOM showed a P0440 code, EVAP system. I disregarded it because most of the time that is a gas cap. Plus, I thought tgat it had something to do with the fuel filter change.

 

Checking the throttle body would be a good idea. Might need a good cleaning. Check the sensor ports at the throttle body especially the MAF and MAP ports for blockage. Also check the PCV valve and its port into the UIM. Make sure the o-ring is there and properly positioned. If any ports are clogged the sensors can't read properly.

Don't overlook the P0440 EVAP code though. Do you top off your tank when fueling? This can allow charcoal in the EVAP canister to spill out causing blockage in EVAP air vent or vacuum lines, or foul solenoid valves. Check vacuum and air lines in and out of the EVAP canister purge valve for leaks or blockage. Could also have a bad EVAP canister or vent valve. Do you smell fuel at all?




Hope this helps, keep us posted.

 

For the most part, when it is fueled, it is topped off.


I have smelled a gasoline odor here and there, but not enough to cause concern. Well, not until now.


I will look for a vacuum leak this weekend, although it doesn't have an erratic idle normally associated with a vacuum leak. I'll also check the lines to the EVAP canister.


What and where would I find the solenoid valves that were mentioned?


Thank you for all of the inputs.

 

The EVAP canister vent valve (solenoid) is behind the driver side inner fender. Need to remove inner fender to get to it (easy).


The EVAP canister purge valve (solenoid) is in the engine compartment to the right of the ignition coils, between the front valve cover and the fuel rail. Small black plastic valve with plastic hoses in and out. here's some pics.
http://www.1aauto.com/chevy-monte-ca...ts/mo-c/31-240

 

We had a busy weekend, but I took a few minutes Sunday and removed the ait intake, surprisingly clean. I almost tore up the screen trying to remove it, so I'll buy a new one, then pop it off to clean the throttle body.

I found the EVAP solenoid on the valve cover, I'll be replacing that soon and see where we are.

 

Well, I changed the EVAP canister purge valve, because it was the easiest to get to. Anyway, things are a little better, but still there. I'll change the EVAP canister vent valve next.


On the upside, the list is getting shorter and each component change shows improvement. I'll keep you guys posted.

 

Good news bad news.


I changed the second EVAP part, the one behind the left rear tire. While I also changed the plug wires. (I was strapped for time and cash when I changed the plugs.)


Anyway, a full throttle blast resulted in clean, even acceleration all the way to 5500 rpm where it shifted. Previous tests resulted in surging as it revved.


Anyway, I don't know if it was the second EVAP part or plug wires, either way, they needed changed (the plug wires had numbers on them) and now her Monte runs good again. I thank everyone who contributed.