My Car's EGR Valve and Me

Ok, I think to myself, what the heck is THIS?? I was just traveling to my work place and was slowing down for a traffic light when the engine died. This being a straight drive truck, I placed the shifter in neutral and coasted off the side of the road. I gave the key a twist and it started right back up. And died again just as quickly. I cranked her over again, and this time gave it some gas pedal..and she kept running at a fast idle. I let off the gas...and the engine died again. VERY strange behaviour.

If you have never driven through heavy traffic with an engine that wont idle, and trying to keep the engine running while trying to operate the clutch and brake all at the same time, then you have a truly unique experience in store for you.

Back at the house later that day I began to delve into what kind of a problem I had been presented with this time. On the way back I noticed that the check engine light had come on and I intended to pull the codes to maybe determine what had happened. On my old truck pulling the codes is quite easy. You take a piece of wire and skin off the insulation on both ends. Take those two ends and push them into a socket that is set under the dash. When you turn the ignition key to on..the check engine light will begin to flash a code. For me, it flashed a three and then a five. A code for thirty five indicated an egr problem. Not having encountered an egr or Exhaust Gas Recirculator problem before, I had no idea if this would affect the idle. So, off to the store to get a new egr valve.

Back at the house and after a little internet browser study, I found the egr valve lives on the intake manifold. It's job is to introduce some exhaust gases back into the engine combustion cycle to help control emissions. It was simple to replace as it was only held on by two nuts and I soon had it replaced. It made no difference whatever in the way the engine idled. Which got me to thinking..how does the egr do this recirculating thing? Turns out the egr is operated by an egr solenoid. The solenoid routes engine vacuum to the valve when needed..thus opening it. When it opens, exhaust gases can get back into the engine. Maybe this solenoid wasn't working and so this egr could not work either.

Back to the store for an egr solenoid. Back to the house to install the solenoid. Absolutely no difference at all in engine idling.

I was looking glumly into the engine compartment and racking my brain for a fix on this latest problem. This was a T.B.I. type of gas system. Throttle Body Injection. It is really a high tech carb minus the float chamber, fast idle circuit, idle circuit, choke circuit and mixture circuit. All of these functions were now controlled by an on board computer. It regulates everything. If the engine is cold it knows because a temperature sensor told it so and it revs the engine up at idle in cold weather. If the gas/air mix is incorrect it knows this because the oxygen sensor told it so and the computer changes the gas/air mixture via the injectors sitting in the midst of the t.b.i. and brings things back to where it wants them. So why isn't the fraddling thing adjusting the idle? No doubt, because it is unable to do so because...hmmmm. Just exactly how does the computer operate the idle? Looking closely at the t.b.i. squatting in the middle of my intake manifold I spy a lumpy looking thing projecting from the side with a wiring harness attached to it. What is THAT thing I wonder? And look..here is another one on this side. It seems attached to the accelerator cable.

Minutes later I am cruising the internet browser again looking for information. I found what I was looking for and wanted to bang my head against my shins. The idle was controlled by a tiny motor inserted into the t.b.i. This tiny motor has a shaft sticking out and on the tip of that shaft was a cone shaped stud and the motor can move this stud in and out of an idle passage made into the t.b.i., thus adjusting the idle at any given time. In fact, this little motor had two hundred and fifty five steps in it's motion. The computer controls it all. All I had to do was replace this little motor by threading a new one in. Which, after yet another trip to the store I accomplished and started the engine up..and listened to to it run with great pleasure as it idled perfectly. Then that check engine light came back on !

This was too much. A new egr valve. A new egr solenoid. A new air idle motor. What next? I pulled the codes again and the result was the same as last time. An egr issue. Having done some homework now I felt I had a good handle on what these emissions controls did.

Everything seemed to hinge on the oxygen sensor. This device sits in the exhaust stream. It looks for an a precise level of oxygen. If the level is too high, it knows the engine isn't getting enough fuel or an incorrect timing issue is causing the incorrect level..so it will adjust the fuel and timing.

If the oxygen level is too low, the computer will adjust fuel and timing to bring the level to where it knows it should be. And if it fails to bring this level to specifications...then you get a check engine light so you know there is a problem. It appeared that this is where I found myself at the moment.

Well, the engine was running fine so I decided that over the next few days I would look into the matter again. And so it went. I replaced the oxygen sensor. I replaced the M.A.P. sensor. Then I replaced the knock sensor. And then I replaced the ignition timing module. And none of it worked to rid me of that check engine light. I finally came to the conclusion that the engine had so many miles on it, that it was past bringing it back into line emissions wise. Too much wear on the rings and valves and such. The check engine light would just be a permanent fixture on my dash. Besides, a small piece of electrical tape over it..and I would never know it was on.