My engine is loping at idle speed. Also, I now have to pump the accelerator to start it (warm and cold), where I didn't before.
OBD was showing a P0401 (EGR flow insufficient) before this happened. I was going to check the EGR valve but didn't get around to it. Now I'm getting a P0402 (EGR flow excessive).
I'm not sure if the 402 is a symptom the cause. EGR flow shouldn't affect the engine starting, should it?
My Haynes manual shows a number of causes for the engine idling inconsistently. The first of which is vacuum hoses. It directs me to check the vacuum hoses near the throttle body. Question is, what does a vacuum hose look like? To what would it be connected?
Iffen the EGR is stuck open it will make it hard to start and have a crappy idle, if it will idle at all. A vacuum hose is just a piece of rubber tubing attached to the intake manifold for vacuum source, and attatched at the other end to a vacuum operated device, such as the power brake booster, or the mode select valve on the heater plenum.
One way to check the EGR operation is to have the vehicle idling, and open the EGR valve by pushing on the diaphragm. The engine should die or react with poor running, and clean up when you release the EGR. You can also disconnect the vacuum line hooked to the EGR valve, and plug it with a golf tee to see if the engine runs better..
Sounds like your EGR valve is sticky, gunked up. If first you got the error code indicating INSUFFICIENT FLOW, then later, EXCESSIVE FLOW, the valve is "hanging up". Like "tomw" said, it will idle like crap (if it runs at all) when the valve is stuck open, but will run well when the valve is stuck shut (you might not even know it's stuck shut if the computer/check engine light didn't tell you). If indeed it turns out to be the EGR valve for sure, you might be able to salvage the existing one by gushing it out with WD-40, and working it manually to dissolve gunk & free it up. Let us know how it turns out.
I think I've found the EGR valve itself, but I want to make sure. I defintely found the EGR transducer. It's got two rubber tubes attached to it that run to a metal pipe which in turn runs to the manifold.
Now the other end of that pipe runs toward this circular object. The circular metal object has a tube running off it that runs to a rubber object attached to the engine. This rubber object has another rubber tube which runs behind the engine somewhere. The circular metal object is attached by two bolts to another metal pipe which leads right behind the throttle body. I believe this circular object is the EGR. I'll find out at least when I take it out today =)
It may be the EGR, but then again like your Haynes manual stated, it could be a vacuum leak. That's what my problem turned out to be. The upper radiator hose totally split open a main vacuum line. I replaced it and solved the problem. She runs like new again. By the way, it was my 2002 4,0 Ranger.
Start her up, and listen for the hiss of a leak. As your Haynes manual describes, use a stethescope or a rubber hose to pinpoint the leak if you have to.
Last edited by Tomm; 08-15-2008 at 08:30 PM.
Reason: more detail