2000 Saturn SL1 acceleration problems

STACEYHOWARD

MEMBER
2000 SATURN SL1
4 CYL
FWD
AUTOMATIC
85,000 MILES

My 2000 Saturn has had all the regular maintenance done, including a full tune up and servicing in Sept 2008. Recently the engine starting increasing rpms when the car was put into park or neutral. At first the problem was intermittent. Now the engine revs all the time, running at about 2500 rpm, although once in a while it goes back down to 1100 rpm. I can drive down the road at 35 miles an hour without ever touching the accelerator, and in fact even have to brake to slow down sometimes. I was told it could be vacuum hoses or o2 sensor, but this doesn't make sense, as the o2 sensor was changed in 2006. I have only owned the car a little while, but the previous owner claims no knowledge of the problem and gave me all the maintenance records. Now the car is starting to misfire as well, again, even though it had the recent tune up.

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.