Under the Hood: Getting to the bottom of a rough-running engine

McClatchy-Tribune Information Services

June 20, 2018

Q: 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?

ó Karen

A: 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 gasses 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 vacuum operated EGR valve (addressed here) and others use a purely electric EGR, which isnít prone to the problem Iíll mention.

EGR is not supposed to occur when the engine is cold, or when itís 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 solenoidís 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 ó if EGR isnít 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, donít worry; itíll 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).

I should add that an engine that idles rough cold or hot may be the result of an EGR valve that does not fully close. The cause is often a build-up of carbon on the valve seat. Rough running while under way can result from a faulty EGR position or exhaust pressure sensor.