Engine suddenly stalled

[Falcon_LS]

This was on my Grand Marquis. I was at a car wash last night, waiting for my turn in line. At one point I turned off the air conditioning, since the weather was better, and I was idling in neutral with the parking brake on.

When it was my turn to move forward, I shift into drive and by the time I just lightly hit the gas pedal, I noticed I was rolling backwards (slight slope) and was about to hit the car behind me. Hit the brake, applied the parking brake again and she fired right up.

Also, no idea if this is related, but I also noticed the voltage gauge dropping slightly when I apply the brakes.

Haven't been able to check with my multimeter yet, but this never happened before, so it's got me wondering. Runs as smooth as butter, no drop in performance, no CEL or anything. Thanks!

 

[Summerwind]

Sounds as though that for whatever reason when you put her in drive, your idle may have dropped too low and stalled the engine? Just some quick suggestions here, has your MAF sensor been cleaned recently? And since you said your voltage dropped some when you applied the brakes, I'm wondering if your alternator could be getting "lazy" and not supplying enough voltage to keep things going? I had that happen infrequently on my old Cutlass, and several weeks passed before it finaly just "Quit"..

 

[Falcon_LS]

I cleaned my MAF roughly 2,500 miles ago actually, and a new (rebuilt) Motorcraft 130 amp alternator fitted about 3,200 miles ago.

Maybe I need to check my ground cables? Could it be the IAC? I've had rough idle not too long ago when the engine was cold, and it went away after I revved up the engine slightly.

 

[Summerwind]

Sounds like a good place to start..Its funny, have a GMQ also, but my Cutlass is experiencing some idle issues occasionaly like your GMQ is, and its been a while since I cleaned the IAC on it also.. I forgot that yours has one of those on it!

 

[StevieC]

Check Idle Control Motor. Might be sticking.

 

[Colt45ws]

*insert annoying post with "IAC" copied into it 50,000 times*

 

[firefighter]

Falcon-LS,
Check your throttle plates for build up, Your IAC might be getting sluggish, then when you pulled it into drive, computer thought Xamount of air was comming in and it was not because of the build up on the throttle plates and the car stalls.

 

[demarpaint]

Originally Posted By: firefighter
Falcon-LS,
Check your throttle plates for build up, Your IAC might be getting sluggish, then when you pulled it into drive, computer thought Xamount of air was comming in and it was not because of the build up on the throttle plates and the car stalls.


+1 Then make sure all grounds and connections to that alternator and battery are clean and tight.

 

[jim302]

If the alternator itself was bad enough to cause the car to stall, it probably would have drained the battery enough to cause problems with re-starting it. Then again, electrical problems can be crazy... good luck!

I'm thinking it is most likely a bad ground connection, bad/dirty IAC (most likely), or possibly even a clogging fuel filter.

Have you considered using a code scanner to see if there are any pending codes that haven't triggered the MIL yet? Usually the fault (if any) has to happen a few times before the light turns on.

 

[punisher]

Originally Posted By: Colt45ws
*insert annoying post with "IAC" copied into it 50,000 times*

Sadly you know this forum too well.

Unless it does it again, ignore it.

 

[mechtech2]

Clean your throttle plate and bore first with solvent and a rag. Get them really clean.
Then maybe the IAC, but be careful about strong solvents here.
Power and ground cables have TWO ends, not just the battery. Make them and where they seat clean and shiny!
Of course, check for codes.

 

[Falcon_LS]

Thanks very much for all the input!

Update on the situation, whilst it never happened again, I pulled the IAC valve yesterday and it was as clean as a whistle (I use TC-W3 in the fuel). Also appeared to have been replaced recently, as it looked new. Throttle body was also clean, but I cleaned it up a bit anyway, as well as the MAF. Also cleaned up the positive/negative cables with battery cleaner whilst I'm at it, making sure they are all tight. Stalling never happened again, although there's still a slight drop on the voltmeter when the brakes are applied. Will need to get somebody to apply the brakes whilst I have my multimeter out.

 

[Vikas]

By the way your fuel never touches IAC valve, using TC-W3 or MMO in the fuel will not do anything to IAC.

 

[punisher]

Originally Posted By: Vikas
By the way your fuel never touches IAC valve, using TC-W3 or MMO in the fuel will not do anything to IAC.

I remember a FoMoCo bulletin about cleaning IACs. The metal bodied ones could be dissassembled and the valve/pintle flushed with solvent. The plastic ones weren't to be cleaned due to solvents causing degradation of the plastic components.

 

[mechtech2]

The voltage SHOULD drop at idle with the brakes applied.
Some more or less - but some is expected.

 

[CROWNVIC4LIFE]

Same thing happened to me today while waiting for a very long freight train to pass...It fired right back up again....Now that I think about it my 99 did the same thing once or twice a year...I never figured out why it did it...No codes or anything...Not worried about.

 

[rslifkin]

It was just trying to save you gas while waiting!

 

[Colt45ws]

Originally Posted By: CROWNVIC4LIFE
Same thing happened to me today while waiting for a very long freight train to pass...It fired right back up again....Now that I think about it my 99 did the same thing once or twice a year...I never figured out why it did it...No codes or anything...Not worried about.


Electronic throttle control. If it fails you will have a high idle and nothing else.

 

[punisher]

Once in awhile the evap purge valve can cause a stall during decel/idle.

 

[demarpaint]

Originally Posted By: mechtech2
The voltage SHOULD drop at idle with the brakes applied.
Some more or less - but some is expected.


+1 and with older cars the greater the load, the more the drop. Typically in bad weather when accessories like, defroster, wipers, rear defroster, heated seats, etc will cause a voltage drop at idle. Alternator output plays into it as well.