About a week ago, I noticed that when I’d be sitting at a red light, my engine RPMs would fluctuate, maybe from 800-1200. Normally I wouldn’t have thought to much of it, but I can hear a relay clicking each time thje RPM’s are on there way up. I did a little research, and I’m thinking it’s the EGR valve stuck open from carbon. So first, does that sound right?
Second, why only in drive, it doesn’t do it in neutral?
Third, (this is the one that worries me), it doesn’t do it if the AC is off which makes me wonder if it has something to do with the AC clutch. Any ideas before I replace a $70 part?
I would not go buy a new EGR valve just yet.
EGR is used at part throttle cruise conditions to control the oxides of Nitrogen by recalculating a small amount of exhaust gas into the intake stream. Oxides of Nitrogen are only created when the combustion temp gets over 2500F. This only occurs at part throttle cruise when the engine tends to run lean.
For this reason EGR is not required or needed at full throttle or at idle. EGR valve can stick either open or closed. If they stick closed, there most likely will be no drivability complaint, but you will have a check engine light to notify you of the failure.
When EGR valves stick open you will either have a very rough idle, or perhaps no idle at all and the engine will die if you try and get it to idle. This in fact is a check to see if an EGR valve is working, activate it at idle and see if the idle quality goes to hell. If it does, the valve is OK.
Idle hinting from 800-1200 with a click under the dash does not make me think EGR valve. Some GM cars use an electric EGR which could have a relay as a controller, but I always thought they were directly controlled by the ECM. Functions controlled by the ECM don’t click. Relays sometimes do click.
The hunting and clicking stopping when the A/C is off makes no sense if it were the EGR.
This leads me to believe that it is not an EGR issue. I think it may be an A/C issue. A/C clutches are usually controlled by a relay, when the clutch disengages a large load is taken off the engine, and idle can flare, when the A/C system is low on gas, the clutch will cycle excessively. Go look under the hood, and watch the A/C clutch does the surging coincide with the clutch cycling?
If you are still convinced that it is the EGR, you can unbolt the EGR valve, and make a plate to bolt in place of the valve. Bolt said plate in place. Start the engine, idle in gear with the A/C on. If your idle still surges, and you dash still clicks, it’s not the EGR.
There is a much greater load on the engine when in gear. Makes things like the A/C clutch cycling much more noticeable.
Do you have a check engine light on?
The clicking you hear is not a relay, but the A/C clutch engaging. It doesn’t make a noticeable noise when it disengages.
The system is designed to raise the idle speed when the clutch engages, as the A/C compressor load would otherwise pull down the idle speed. It doesn’t need to do this in neutral, and it obviously won’t do it with the A/C off.
The frequency of the A/C engaging/disengaging suggests it’s low on freon, which would also reduce the compressor load and make the speed change more noticeable.
While it’s true that an EGR valve stuck partway open can affect idling, and maybe even cause some fluctuation, absolutely none of the details in this case support the notion that this is the problem. In fact, they pretty well disprove it.
Don’t buy an EGR valve. Have your A/C system checked.
I think that’s what I’m going to have to do. I’m quite sure it’s not the EGR valve anymore. There’s atleast one place around town that does free AC checks in the beginning of summer. I’ll have to wait until I hear the ad again to see if it’s a store I trust or not. My AC does still blow cold air, so that’s a good thing though.
I’m sorry, but I do not feel as if this is exactly correct, although it’s somewhat correct within the boundaries of the situation. NOx is produced as a function of the partial pressure of oxygen (availability of oxygen), the fuel-bound nitrogen content (and presence of additives that influence free radical N’s), the devolatization characteristics of the fuel (more free radical N’s during the initial molecular chain breakups), and the temperature of combustion (mean and peak). The tendency, all other things being equal, is for NOx production to be very strongly increased at higher temperatures, lean conditions, or both. However, NOx is produced to some extent at most all throttle positions and engine loads (low-load + rich conditions possibly excepted), and part-load NOx is still something that a modern engine is tuned to try to reduce at standard motoring loads - since after all, your engine likely spends most of its time there.