2000 Buick Lesabre High idle at startup

HORNADYLNL

MEMBER
2000 BUICK LESABRE
6 CYL
FWD
AUTOMATIC
90,000 MILES

I have a 2000 Buick Lesabre. It idles around 1400 rpm when I start it up from being cold and takes several minutes before it comes down to normal. I've replaced the IAC and that didn't help. I had a vacuum line that sits on top of the front valve cover and intake go bad. I replaced it. I don't think it is a vacuum problem because the engine falls on it's face if I unhook a vacuum line. A dealer mechanic said these cars were prone to having a broken wire going from the IAC to the computer.

I haven't replaced any of the temperature sensors on it. I believe there are several. Any idea which one would be responsible for sending temperature to the computer? This car has a temp guage in it as well and it seems to work fine.

I'm wanting to get this fixed as it causes a hard shift when I start it up. I just noticed today that it is shifting hard while I'm driving. I'm going to have the tranny flushed with the BG system to see if that solves the hard shifting problem. Thanks for any input.

3 Replies

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.