The SES light comes on my 94 Camaro, 3.4L (160k) intermittantly, generally when the engine is warmed up, and most often at high speed on the highway when I brake after hard accelleration. It's never come on during hard accelleration, only afterwards, usually braking but sometimes coasting. Usually goes away after driving a little further, always when I restart the car.

It's been happening for about 3 years now- no change in performance or mileage, though the car does have a rough idle and there's a high pitched whine from somewhere in the engine, which may or may not be related. The light has been coming on more and more frequently and at colder temperatures as time has gone by. I tried replacing the O2 sensors and it stayed off for 2 days, but is back on now.

Ideas?

 

Sounds like a vacuum leak. During acceleration there's so much vacuum in the manifold as the engine sucks in air that the sensor doesn't trip. When you decel the motor is near idle and the momentum of the car on braking pulls the hoses forward ever so slightly. It can be just enough to trip the sensor. This would also explain the erratic idle as vacuum is one of the factorsused to set idle speed. I'd check for a vacuum leak. Could be something else but I'd start there.

Thanks,

Tom

 

The PCV inlet was loose (I didn't get it seated quite right after removing & reinstalling the intake plenum when I changed the water pump last weekend), but I don't think that was the problem.

I'm thinking more and more it's the EGR valve. The high-pitched whine that I thought was coming from the alternator isn't; I changed the alt, and it's still there. It's coming from around the area of the EGR. When I gun the throttle, it stops momentarily. When I slowly change rpms, it changes pitch, and when I drop the rpm quickly, the change in pitch is delayed. So, could be a vacuum leak, but there's very little by the way of vacuum in that area of the engine.

Is there an easy way to test/clean this?

 

Supposedly you can test for leaks by spraying engine hot start spray in the areas where there may be leaks. I've never tried this myself. Sounds a little dangerous. But the theory is if you spray it on a hose area and the rpm suddenly rises you've found your leak. Make sure you have an extinguisher handy and wear heavy cotton clothing. Keep your good polyester suit away from this test Ha! Ha! Who knows it may be a safe way of doing it but I've seen in other posts that that is the way to do it. If you don't have a Haynes manual for your car yet get one. It's invaluable. Hope this helps.

Thanks,

Tom

 

I managed to track down the leak to (I *think*) somewhere beneath the intake manifold, possible coming from one of the fuel injectors. Which is to say, I used a vacuum cleaner hose as a stethescope, and that's sure where it sounds like the whistling is coming from. Is that a common source of vacuum leak? How the heck would I fix that? Is there anything else down there that might be causing the whistle?