Solving an engine that chugs at low speeds

Question: I have begun to have a problem with my 2001 Ford Escape with the V-6 engine. It starts fine in the morning and runs OK for a few miles, and then it begins chugging and loping when I come to a stop. It also hesitates to take off but then drives OK again after I get to higher speeds. Any idea of what could be the cause before I make a service appointment?

K.B. Answer: There are many possible reasons for an engine to idle rough or hesitate on acceleration, but most of them would occur at all times. Your comment that the engine runs fine for a short time before acting up leads me to focus on the EGR system. This is an emission control strategy that allows a small quantity of exhaust gases to be recirculated through the engine a second time. Adding a small, carefully regulated quantity of exhaust to the incoming air-fuel charge reduces combustion temperature, and the formation of NOx, a nasty emission compound.

I wrote about this a while back, regarding a GM vehicle, but have since heard of quite a few other makes and models of vehicles encountering similar issues. Many but not all vehicles have EGR, some use a vacuumoperated EGR valve (addressed here) and others use a purely electric EGR, which isn’t prone to the problem I’ll mention.

EGR is not supposed to occur when the engine is cold, or when it’s idling. If it does, engine roughness such as you described may occur. Since your Escape runs well when the engine is cold, it appears the computer controlled electric solenoid (valve) controlling the EGR valve is functioning normally.

What I believe may be happening is the control solenoid’s vent filter has become restricted, which causes the EGR valve to linger open when the engine returns to idle. This is a serviceable and inexpensive part, located beneath a removable black plastic cap that snaps onto the top of EGR control solenoid. Unsnapping the cap reveals a removable foam thimble, which can be either cleaned or replaced. Try removing the filter and drive the Escape for a short time without it to see if this corrects your idle loping/roughness symptom.

On other vehicles with a less obvious vent filter location, or perhaps a non-serviceable integrated filter, one can temporarily disconnect and plug the vacuum hose leading to the EGR valve (its location, along with that of the control solenoid, should be indicated on the under-hood emission control information label — if EGR isn’t mentioned, the vehicle likely does not have one).

Try driving the vehicle for a few minutes to check for a difference in performance. If it markedly improves, an EGR fault exists. If the check engine light illuminates, don’t worry; it’ll go out within a day or two and the stored trouble code will self-erase in about two weeks. Long term disconnection of the EGR is not advised, as it is illegal, increases emissions and may lead to engine-damaging detonation (spark knock).

Q: I had an oil change at a dealer and drove about 1,000 kilometres. After leaving work, I drove about 20 km when the check engine light came on and the engine seized. I had it towed to a nearby dealer and they called saying the oil filter was missing. Where did it go? They said it was vandalism. That means while I was working someone crawled under my van and loosened my filter. Any thoughts?

J.F. A: Yeah, I think that the filter was not properly tightened during the oil change. Unless you have some evil enemies, I doubt that vandalism was the cause.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers cam email him at bradbergholdt@gmail.com; he cannot make personal replies.