Q I put a small amount of power-steering fluid into the brake-fluid container of my car by mistake. Please let me know whether it would cause any problem with my brake system and what I should do to correct it.

A Most brake fluid is glycol-based -- the exception being silicone brake fluids used in some high-performance vehicles -- and power-steering fluid is petroleum-based. They are not compatible. Exposure to petroleum products can cause rubber brake components to swell, leading to potentially serious problems.

In cases where contamination has just occurred, the brake system needs to be completely drained, flushed with denatured alcohol, refilled and bled with the proper brake fluid. In this case, quickly siphoning the master cylinder reservoir may remove most of the power steering fluid. If contamination has spread throughout the hydraulic system, you'll have to replace or rebuild major brake components, including the antilock braking system's hydraulic control unit.

Q I have a 2000 Dodge Grand Caravan with a 3.3-liter V6 engine and 116,000 miles on it that I bought new. My problem is a mild miss at idle when the engine has been restarted after it has warmed up. It will do this in gear or neutral at idle, but does not miss at any RPM above idle or while you are driving it. It was tuned up last year with new platinum plugs and wires, and the dealer cleaned the throttle body. It does not miss after a cold start. The check-engine light hasn't come on. Fuel economy has been pretty constant since new.

A Are you sure it's a misfire? With the engine warmed up, any significant misfire should trigger a diagnostic trouble code, lighting up the check-engine light. Make sure the new spark plugs are the correct double-platinum original-equipment plugs.

Start by checking with a scan tool for stored fault codes. If none, check for a leaking fuel injector or fuel-pressure regulator with a fuel-pressure leak-down test. If residual fuel pressure drops rapidly after shutting off the engine, pinch off the fuel supply and return lines near the firewall with soft-jawed vise grips and retest. If pressure at the fuel rail drops rapidly after shutdown, suspect a leaking fuel injector. If pressure holds at the fuel rail, suspect a fuel pump or fuel pressure regulator problem in the fuel tank.

Check to make sure the evaporative emission system purge valve is operating properly, and that there is no intake system vacuum leak.

Also, check cylinder compression or have an electrical cylinder balance test performed. A weak cylinder, leaking valve or worn camshaft could also cause this symptom.

Q I have a 2003 Hyundai XG350 with 80,000 miles. In the past six months I have noticed some clunking in the automatic shifting when I accelerate to about 20 miles an hour. It will happen in winter and summer, unless I accelerate quickly or unless I let the car warm up a bit.

A The dealer's service computer can check for transmission fault codes and perform sophisticated diagnostics on the quality of each upshift. It may be possible to reprogram the adaptive values in the transmission control module.

It's also worth checking both front-drive axles and their constant-velocity joints along with the engine/transaxle mounts for wear and play.