Q My '01 Impala with the 3800 engine has 122,000 miles. For the last two months, it has began to surge rhythmically at about one-second intervals when accelerating from a stop sign or to maintain speed.

It does this whether in or out of cruise control and at speeds from 30 to 70 miles per hour. It doesn't do it consistently, but rather off and on. I can feel the surge in the seat of my pants, and I can see it on the tachometer, which will swing as much as 300 or 400 revolutions per minute. As soon as I stop accelerating, the surging stops.

I've used four bottles of fuel-system cleaner in as many tanks of regular gasoline, thinking it is a sticky fuel injector or maybe even a valve. This doesn't seem to help. Several mechanics think it still is a sticky fuel injector.

A A sticky or partially clogged fuel injector could well be the cause for this hesitation, or "chuggle," as it's often called. With an rpm change of 300 or 400, it could also be the torque converter clutch locking and unlocking for some reason.

A quick test for this would be to use your left foot to depress the brake pedal about half an inch -- not enough to actually engage the brakes, just enough to activate the brake switch -- and hold it at that point while you gently accelerate. If the chuggle disappears during this test, the problem is with the converter clutch or its "command" from the powertrain control module.

If this simple test doesn't change the symptom, the problem could be a faulty throttle-position sensor, restriction in the air filter or induction system, or a clogged injector. GM's special upper engine and injector cleaner may help clean a dirty injector and restore its performance.

Q My wife has a 2000 Dodge Intrepid. She overfilled the gas tank, and now we can't put gas in very fast. I would like to know what to do to remedy this problem.

A Overfilling the fuel tank may not be the cause of the slow-fill syndrome. My Alldata database pulled up technical service bulletin 14-001-03, dated January 2003, that deals with this symptom. Anytime the fuel tank will accept fuel only very slowly, it's a lack of proper venting during refueling. As fuel enters the tank, the volume of air displaced by the fuel must be vented. The first things to check are the tank vent lines and fill tube assembly for any blockage. In this case, the service bulletin also identifies the possibility of a stuck fuel tank control valve or a clogged leak detection pump filter.

Q The battery cable going to the positive terminal of the battery on my '96 Tahoe attaches to the side. Periodically it comes loose. For example, I might back out of a parking space, put it in drive -- and it suddenly dies as if the battery were dead. I get out and tighten that bolt real tight, and I'm good for weeks or months until it happens again.

I've talked to other Chevy owners who've had the same problem, but no solution. Do you know of some relatively easy fix, other than replacing that whole cable?

Also, the metal plate shielding the plastic gas tank rusted away and fell off. Is there great danger in operating the vehicle without that shield? I've lived without it for more than a year now.

A We've had the same dead-battery syndrome with our '96 Tahoe as well. After "futzing" -- the official term for repeatedly failing to fix the issue -- I replaced the special 5/16-inch head bolt that secures the battery cable to the battery. In addition, I thoroughly cleaned the contact surfaces of both the battery and cable, and used a small screwdriver to bend the small tabs on the contact surface of the cable out a bit to help them make better contact with the battery terminal. So far, so good.

As far as the missing steel fuel tank shield: I guess it's dangerous only if something tries to punch a hole in the tank! I think you should try to find one at a salvage yard -- I'm sure it would not be expensive -- and install it on your Tahoe. Better safe than sorry.

Q I have 106,000 miles on my 2000 Toyota Avalon. Toyota recommends replacing the timing belt at 90,000 miles. Do you think replacement is absolutely necessary? Do timing belts routinely fail? I understand that I have a non-interference engine, so timing-belt failure would not destroy the engine.

A Toyota recommends changing the timing belt at 90,000 miles or 72 months. And you know me; I'm a firm believer in preventive maintenance. Even though this 3-liter V6 is not an interference engine, I still would suggest changing the timing belt, especially if you plan to keep the vehicle for several more years.