Mechanics

ENGINE RACES WHEN FIRST STARTED

2001 Pontiac Grand Am • 2WD Automatic • 85,000 miles

What makes the car motor race when first started
Avatar
Momt
March 14, 2011.



Your foot is on the gas pedal. Gas pedal is catching on the floor mat. Have you done any preliminary tests or made any observations? It is normal to go to around 1500 rpm for one or two seconds. That's called the "idle flare-up". If it lasts much longer, you might suspect a defective coolant temperature sensor or intake air temperature sensor. A sticking idle air control valve can cause a delayed drop in rpm after starting but it will usually also cause stalling after an abrupt stop. Also look for a vacuum leak but they rarely stop leaking after the engine is warmed up. A vacuum leak should cause high idle all the time with low engine power and the Check Engine light will turn on.

Caradiodoc
Mar 14, 2011.
NEVER had to put foot on the gas pedal even in zero weather. No way for the pedal to catch on the floor mat. Took the car to 2 different repair shops without the problem being solved. If it is zero, the car starts normally, but driving it a few blocks the restart sounds like the indy 500. If the weather is warmer, the first startup is pretty loud. After being driven about 10 plus miles, a restart is normal unless it has had time to cool down too much. Losing approx
3 mpg on 20-30 mile trips. Had to drive 110 miles and got 30 mpg. Got 32 when first bought in 01. Really would like to keep this car, but I know that this problem is hard on other parts of the engine.

Tiny
Momt
Mar 14, 2011.
Hmm. So what exactly do you mean by "race when first started"? Do you mean it's idling too fast or too loud? If it is loud, the obvious thing to check first is the exhaust system for leaks, but if it changes with engine temperature, look closer at emissions-related tubes. GM front-wheel-drive cars are much louder than most other cars anyway but will get even noisier when some of the emissions items turn on and off if there is a leak. It's probably best to not let that go too long because if it is a leak in an emissions system component, it could be allowing exhaust gas into the car. We want you to be around to ask another question in the future!

Caradiodoc
Mar 14, 2011.
Idling too fast. There has been not smell of exhaust at any time. The startup does change with enfine temperature. This is a recent problem. Did not do this previously.

Tiny
Momt
Mar 15, 2011.
Idling too fast means too much air is entering the engine. There's only two ways that can happen. One is through a vacuum leak in a vacuum hose or an engine gasket around the intake manifold on top of the engine. Sometimes you can hear a vacuum leak but first you have to know what "normal" sounds like before you can recognize "not normal". When it's idling too fast you can try pinching various vacuum hoses to see if one brings the idle speed down. If one does, follow it and pinch it in other places to locate the leak. While the engine is running and still fairly cold you can spray water on the gaskets. If you see a place where it gets sucked in and the engine slows down, you found a place to look closer for a leaking gasket. The second way for extra air to enter is through the idle air control valve on the throttle body. It is controlled by the Engine Computer and lets just enough air in to hold the idle speed at the desired level. In rare occasions it can stick after starting the engine so the idle speed won't come down to normal after providing the nice "idle flare-up" to 1500 rpm for a few seconds at engine start-up. You would find this by connecting a scanner to view live sensor data while the engine is running. If the Engine Computer is trying to reduce engine speed it is not having success. The idle air control motor and its wiring would be the place to look. If the computer is really trying to increase engine speed it is doing it in response to something it is seeing from some other sensor.

Caradiodoc
Mar 15, 2011.
Thanks. This is the kind of answer that might help.

Tiny
Momt
Mar 16, 2011.