Bouncing idle at start sometimes...

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Feb 7, 2009 | 01:28 PM

SleeprLegend

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Mountain Pass

Joined: Jan 2006

Posts: 249

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From: Moody, AL

Bouncing idle at start sometimes...

Last year the original battery died in my 1995 F150 XLT Supercab 5.0. This year the same problem of dead battery and bouncing idle on some starts returned. I have installed a rebuilt alternator, and things have gotten better, but the idle will still drop to almost a stall on some starts. It is usually harder on very cold starts, but sometimes it will start fine cold and bounce the idle on a restart after a 10 minute drive.

I have gone through the Haynes, but before I get into that I am wondering if the dead alternator could have damaged the new battery? Of course a damaged battery would be the easiest fix, so I am hopefull. The Haynes refers to a few areas to cause this problem. I am thinking either a vacume problem, PCV, EGR, or sensor issue. This truck is all origional, with some hacking done by the previous owner, so anything is an option.

Any ideas would be appreciated.

Feb 7, 2009 | 01:39 PM

rob1981

Freshman User

Joined: Feb 2009

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Could be a lot of things , plugs fuel pump wrong size of battery. try full tune up first might be cheapest start

Feb 7, 2009 | 01:44 PM

SleeprLegend

Thread Starter

Mountain Pass

Joined: Jan 2006

Posts: 249

Likes: 2

From: Moody, AL

Quote:

Originally Posted by rob1981

Could be a lot of things , plugs fuel pump wrong size of battery. try full tune up first might be cheapest start

I have been wanting a full tune up for a while. While I'm at it I will test some sensors and replace the VSS. She still has an exhaust leak I have to trace down.

Feb 7, 2009 | 06:52 PM

Freightrain

Lead Driver

Joined: Jan 2003

Posts: 9,893

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From: Ohio

IAC is a good place to start looking. It controls idle speed and if it's gummed up with carbon it will stick. Remove it, clean it and make sure the valve moves easily. If not, replace it. Very common idle issue.

Since you replaced the alternator, the battery should survive as long as you charged it up prior to using it again. The alt is not meant for full charging a dead battery.

Feb 9, 2009 | 08:08 PM

SleeprLegend

Thread Starter

Mountain Pass

Joined: Jan 2006

Posts: 249

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From: Moody, AL

Quote:

Originally Posted by Freightrain

That is what I wondered about the battery. I will pick up a charger tomorrow and let her sit overnight. I have a feeling there is something up with anything that controls the idle due to the odd timing of the problem. This morning it started up fine. I drove 20 minutes and shut it off for 1 hour. When I started it back up it was bouncing the idle to the point where it almost stalled. A light press on the throttle seems to be all it takes to resolve the issue temporarialy.

Mar 5, 2009 | 10:13 PM

SleeprLegend

Thread Starter

Mountain Pass

Joined: Jan 2006

Posts: 249

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From: Moody, AL

I found that my PCV valve had jumped out of it seat. As I pulled on it the plastic broke in the hose. I used a tiny screwdriver to remove the plastic in the hose, but slightly split the hose. I then put in a new PCV valve. Now it will bounce the idle at some times. This is only after a full warm-up and shut down. Now once I put it in gear the bouncing stops. If not it will stop as soon as the truck moves. I know the speed sensor is faulty, so I wonder if this might be a factor. A full tune up is set for the near future. I am going to do new oil filter, spark plugs, plug wires, cap & rotor. This should get me off to a good start. I know a new water pump is needed soon.