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Engine Cranks but won't start up


mreilly6
12-19-2010, 09:59 PM
Hi all,
I've been having trouble with my 1998 Volvo S70 the past few days. I had just bought a new battery for it, installed it and tried to start my car only to find it will only crank. The car never fully starts up. However, the car will run is I hold down the gas pedal as I'm turning it on and it fires up. It sputters a bit right at the start up but then runs smooth as long as I'm holding my foot down on the accelerator. As soon as I let off the gas, the engine cuts out.
So far I have checked the alternator and that checks out fine. I've made the battery is connected correctly and the leads and terminals are clean. And also ran a code scanner and have picked up no codes. I have also looked for loose vacuum hoses and found nothing out of place.

Any suggestions?
Thanks in advance for any help!

-Mike

shorod
12-20-2010, 07:51 AM
Welcome to the forum!

You might have better luck posting this in the vehicle-specific section. If you'd like this moved to the Volvo forum, let us know and someone will move it.

From a general discussion though, these symptoms would often suggest either a vacuum leak (which you say you've checked for) or a failing/failed Idle Air Control (IAC) servo. The IAC provides a path for air to bypass the throttle plate at idle and is controlled by the PCM. This allows the engine to idle faster when it's cold as well as compensate for engine loads from the A/C compressor, large electrical loads, hydraulic power steering at lock, etc. It basically does the same thing you are doing by pressing on the throttle to get the engine started and keep it running when cold.

Newer cars may not have an IAC, instead it may be incorporated in to the electronic throttle control (throttle by wire). However I don't think your '98 Volvo would have the throttle by wire system, so I expect it still uses an IAC.

-Rod

mreilly6
12-20-2010, 11:41 PM
Thanks for the suggeston. Is there any way of checking the IAC?

Here's a video I took mainly for the audio. It's simply to listen to how the engine tries to start up:
http://www.youtube.com/watch?v=z8gH86ZbTT4

swingline327
12-21-2010, 07:35 AM
did it run before replacing the battery?

some makes, such as volkswagon, need programming after disconnecting the battery just to run.

if it didn't run before battery swap you gotta check for fuel, spark, and compression.

shorod
12-21-2010, 07:49 AM
Since it starts when you open the throttle slightly we know it's getting fuel, has spark, and the compression is fine. Have you pulled the spark plugs to see how they look? Are they black and coated with fuel or some other substance? Are they still in good shape, or would the gap suggest they are due to be replaced?

If they are coated with fuel you could try holding the throttle all the way to the floor (Clear Flood mode) which will shut off the fuel injectors and give the engine plenty of air.

There is a way to check the IAC, but you either need the engine idling or you need to a professional scan tool to test it effectively. The IAC should allow the engine idle to remain constant when the A/C is turned on, when the charging system is under heavy load, when the coolant is cold, and when the power steering is at lock loading the engine. It could be tough to hold constant enough pressure on the throttle to mimic idle and carry out these checks. A professional scan tool will be able to tell the PCM to attempt to achieve a certain idle speed and it will activate the IAC to do so.

-Rod

mreilly6
12-21-2010, 07:13 PM
Issue has been resolved.
Turns out the engine had to 'relearn' how to do what it's supposed to. It's idling normally now.
God figure it's something simple like that.
Thanks for everyone's help.

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