PROBLEM: Surge and hesitation between 1500 and 3000 rpm

Affects: All '91 - '93 SR20DE (Sentra SE-R, NX2000 and G20)

If the usual tune-up procedure doesn't take care of the problem, disconnect the EGR valve and plug the vacuum hose leading to it from the BPT valve. Take the car out for a ride, making sure to drive in the same manner that typically causes the car to surge and hesitate. If the problem is no longer present, chances are good that you're experiencing the infamous "EGR Problem".

Remove both vacuum hoses from BPT (right-most disk shaped object behind valve cover). Remove the two philips screws on its top. Push the BPT back toward the firewall. You should see a rubber hose running between the bottom of the BPT and a metal tube. Remove the BPT and rubber hose from the metal tube and set them aside.

This metal tube is connected to the EGR passage and, ultimately, to the exhaust manifold. Exhaust manifold pressure, via this metal tube, operates the BPT valve which regulates the vacuum to, and the opening of, the EGR valve. The less exhaust manifold pressure - the more the BPT valve opens - the more the EGR valve opens. The more exhaust manifold pressure - the less the BPT valve opens - the less the EGR valve opens. Carbon may block this metal tube which causes the BPT to not operate properly (if at all) which causes the EGR valve to operate uncontrollably.

Wait until the car is cold, then spray some carb and choke cleaner into the metal tube to soften up the blockage. Used a stiff piece of wire (a long chunk of 8 gauge wire left over from the big car stereo install will do) to ream out the tube. (*Note: DO THIS WHEN THE CAR IS COLD!! Carb cleaner and a hot exhaust don't mix well.*) Take note of how far you have pushed the wire into the tube before you pull it out. Lay the wire along side the BPT tube to gauge how far down the tube you have gone. When you've pushed the wire far enough down the tube to have reached the EGR tube it intersects, you've probably removed all of the blockage(s)

Wait about 10 minutes for the chemicals to evaporate. Start the car and hold your finger in front of the metal tube. You should feel a steady stream of exhaust coming from it. If not, try cleaning it again.

While you're waiting for the chemicals to evaporate, now would be a good time to remove your EGR valve and clean the carbon deposits from the plunger and seat. I find that the carbon build up eventually gets bad enough to hold the EGR valve slightly open. This changes your base idle speed (TPS disconnected) and can also cause a rough and wandering idle as well as possibly causing your car to stall when you push in the clutch.

Reassemble the system, hook your EGR valve back up and take your car out for a ride. You should find that the problem is gone and your local smog police will give you an award for being a law-abiding smog free citizen once more.