I know that we have some good mechanics and technicians on the site here so maybe you can point me in the right direction.

I have a '97 Lumina with the 3100 motor in it. A couple months ago, it started coughing and cutting out. With work as it is, I just kept driving it since it pretty much smoothed out at speed. More recently, it has gotten worse but now it will either sputter and surge or else race leading me to believe that it's overfueling. My guess is that a sensor has gone out. Hate to spend much money on it because it's a disposable car with over 300K on it and I know based on past experience that as soon as I put much money in it, it will die totally. It just needs too many things to be worth spending a lot of money on; besides, that's money I could put into my CTD. The good news is that I do have a matching parts car with a bad motor so I can swap sensors and other components pretty cheap.

What's your best guess as to what would make a '97 3.1L race and overfuel?

Thanks in advance.

 

Look at all of your vacuum lines, one is probably broken at the clamp or close to it. Carefully inspect around the bottom of the throttle body, and near any IAT or MAF sensors in the air intake plumbing.

At the same time, I'd get some throttle body spray and give the TB a good cleaning.

Let us know what you find.

 

I mentioned this trick to someone else a couple of months ago but it works and is worth repeating. If you think you have a vacuum line problem it can be a pita to find a tiny little crack. To help diagnose this, in a reasonably well ventilated area, take an unlit propane torch and play the propane stream slowly over your vaccum lines, tees etc. It all of a sudden the problem goes away, wherever the propane was spraying is where your cracked vacuum line is.

 

Our old 96 Lumina and the 99 Grand Prix did the same thing...MAF was the culprit on both.

 

My 97 Malibu had a problem with the wiring on the IAT that messed up the fuel economy.

Also the 3100 is notorious for the intake plenum gasket failing and filling the crankcase with glycol. Inspect your valve covers and oil fill cap for vapour. I retorqued the plenum bolts and got mine to stop leaking, but its a known failure point.

 

Thanks for the suggestions guys. I'm not losing any coolant and I just changed oil yesterday and there was no water present so hopefully I'm safe there. I'll go pull the MAF off the parts car and I'll check for vacuum leaks and let you know what I find.

 

I`ll hop on the vac leak wagon also. Being a 97 it`s OBD2 meaning if you had a bad sensor, most likely you would also have a ck engine lamp on. A vac leak can also cause the ck eng light but the fuel trims (overall fuel mixture the ECM calculates) has to be pretty far out of whack, BUT a small vac leak can cause these symptoms without skewing the fuel map out of range. That and GM`s are notorious for their brittle/easily broken hard plastic vac. line (been there myself)

 

Still working in the direction of a vacuum leak but haven't found it in yet. A vacuum leak makes sense because I noticed that since this surging started, the AC/vent vacuum controlled doors close sooner when under acceleration which could signal lower overall vacuum caused by a vacuum leak. I'll keep looking.

I neglected to mention that the check engine light is on because it has been for the last 2 years. Back then it was due to a periodic misfire issue and a tranny shifting issue but I haven't had AutoZone run the codes since then.

 

Periodic misfire could also be related to the vacuum leak. Intake gaskets are a good bet. Get a can of carb cleaner and spray the engine down methodically with it running. If the motor picks up after a spray of cleaner, you found the leak. Even if it isn't intermixing oil and water, it could be pulling enough air into a cylinder to cause issues.

 

I was the same with the Malibu, the CEL was on for a good year until a friend of mine took a good look at the system to find the problem. Amazing how it got better after that.

It does sound like vacuum, but it must be a good leak to affect the AC system on accell.