I'm having a problem with my 91 3.1 Camaro. It will idle fine in my driveway for about 7 minutes, then the idle will start to get rough and starts to drop and the engine will rev up like it's trying to compensate but it can't seem to hold it steady and eventually stalls. All injectors reading 12 ohms. Tested fuel pressure and it held a constant 40 PSI. Vacuum at about 12- 15 in and will hold for a bit after engine shutdown. Replaced ECM and TPS already. IAC fairly new as well. Car does not currently have any exhaust past y-pipe as previous owner told me that he started having idle problems after catalytic got clogged and he removed it and the rest of the exhaust behind it. Car is sluggish to drive when accelerating but runs fine otherwise when foot is on gas and when driving, will stall when braking. I'm learning a lot but still fairly new to working on cars still so any advice would be greatly appreciated!!!

 

Hi Travis , me again (the guy who told you the 2X4 trick for removing your stuck upper manifold) . My thought here is , in a single word , Backpressure !

Or more accurately , the lack thereof .

I believe that with no exhaust behind the Y pipe , not only are you likely pissing off your neighbors greatly , your not holding the exhaust in the pipe for long enough for your O2 sensor to get an accurate reading of the exhaust gas temperature . The ECM , using faulty readings from the O2 sensor , is trying to compensate for what it sees as an errant fuel/air mixture , causing the eventual stall . Get a proper factory exhaust on it (or delve into the world of ECM tuning) if you want it to stop stalling at idle .

 

Thanks! Yep, the neighborhood is fully aware of my car at this point. I've got a full exhaust kit currently sitting on my porch that I need to get to installing. That makes sense, though wouldn't the ECM be throwing me a lean or rich or error code if it was having a bad reading?

 

FPR may be ruptured and leaking.

 

I saw another forum that said you can monitor your O2 sensor readings by putting a jumper on your ALDL like when you’re checking codes. Well doing this showed the car starting in normal open loop but wasn’t pulsing normally when it switched to closed loop. Almost looked like it was giving me a code 14 with one long pulse and 4 short ones. I didn’t think it could give codes while running and a 14 is for coolant temp which appears to work fine. However, while I had this jumpered, the car ran perfectly. Idle was constant and vacuum was at normal operating level, which makes me believe you were correct in it being lack of backpressure on the O2 and not the FPR. I don’t know if using the jumper bypassed the O2 sensor or put it into some other mode, but when I restarted the car without the jumper, the idle was erratic again and it stalled.

 

Still haven't gotten around to installing exhaust but a few strange things to add. Car still dies after 7 minutes or so. I unplugged the 02 sensor to see how that would affect the shutoff time but that didn't seem to make any change. It still died right around 7 minutes. Also did not throw any codes with the 02 disconnected or connected. But when I have the A+B ports jumpered on the ALDL, the engine idles so much smoother. Also, the car has started to backfire when I press on the gas while in park in my driveway. Could this be a new symptom related or just from very old gas in the tank? Haven't added gas since I got the car last July, as it hasn't been very drivable since then. Didn't add any storage additives since I didn't expect it to take this long to fix. Almost empty now from test running so planning on getting some gas soon and adding some seafoam through to hopefully help clean it out. Any advice?

 

I am having a similar problem with the 3.1 in my Beretta. Get a fuel pressure gauge and see that you have at least 38psi running at idle, should prime to 40-42 psi as well. Other than that, may have an ignition control module going bad under the distributor cap. Would be worth while to pop the cap and check for corrosion as the module grounds to the distributor base.