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Technical Q&A. HOW TO's, TSB's & Warranty Items Have a Problem? Technical Questions & Answers. HOW TO's & TSB's, Warranty Issues

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Old 08-14-2012, 02:53 PM   #1
mufftang66
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RPMs drop and car dies coming to a stop...

2003 Mach... when I have the ac on and driving down the road, coming to a stop, press the clutch in, press the brakes... sometimes the RPMS will drop down and the car will die. The RPM drop is noticeable, sometimes it will come back up if it doesn't drop far enough to stall out.

It just started doing this last week. After it died a few times, then the service engine soon light came on. I was out of town and drove it home all the way without problem as long as the AC was off.

So I disconnected the battery a few minutes to clear the light, then drove around some more to see if it would happen again and it did.

I checked the air filter, not particularly dirty. I didn't pull it out to check the MAF sensor area yet. I do have the IAC plate that was sold on here... but it's been in the car pretty much since it was new... so almost 10 years. I have not pulled the IAC to look at it yet.

So shadetree mechanics what say you? Any words of wisdom before I take it somewhere to have it diagnosed. Thanks!
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Old 08-14-2012, 02:59 PM   #2
mufftang66
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Re: RPMs drop and car dies coming to a stop...

and in the meantime I did a search and I'm now perusing this thread here..

http://www.mach1registry.org/forums/...drops+car+dies
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2003 Mach 1 5spd : Zinc Yellow
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1966 Coupe 302 auto : Vintage Burgundy


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Old 08-14-2012, 09:01 PM   #3
mufftang66
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Re: RPMs drop and car dies coming to a stop...

I pulled the MAF and cleaned it with CRC MAF cleaner, changed the air filter while I was at it... I also pulled the IAC, nothing to see there really.

This is a stock intake, stock filter...

Still dieing, especially when turning the steering wheel... that is the nail in the coffin, like turning into my driveway. And none to safe actually.

So maybe just replace the whole IAC? I dunno
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2003 Mach 1 5spd : Zinc Yellow
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1966 Coupe 302 auto : Vintage Burgundy


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Old 08-14-2012, 09:06 PM   #4
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Re: RPMs drop and car dies coming to a stop...

Mine does this, has for a while. I am just in the habit now of engine braking when coming to a stop. If I downshift enough and am going less than 10mph or so I find I rarely see the rpms drop at all when pushing the clutch in all the way. If I try to come to a stop suddenly from a faster speed while pushing the clutch it will stall almost every time.

Ive just gotten used to it like I said and changed my driving habits with the engine braking.
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Old 08-14-2012, 09:52 PM   #5
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Re: RPMs drop and car dies coming to a stop...

Any codes? My car did the same when my frps went out. (I doubt thats your problem) When the last time you changed fuel filter, plugs, o2 sensors?
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Old 08-15-2012, 12:21 AM   #6
mufftang66
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Re: RPMs drop and car dies coming to a stop...

I've never changed any of those things... car has about 55k miles on it

next time the check engine light comes on I guess I'll get the codes read.
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2003 Mach 1 5spd : Zinc Yellow
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Old 08-15-2012, 01:28 PM   #7
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Re: RPMs drop and car dies coming to a stop...

At 55k your definitely in need of a new fuel filter & plugs. The filters are around $15 and can be changed yourself. I don't know what plugs to recommend since you are NA. But also bad 02s can make your car run like chit! The o2 sensors are the most expensive out of the three but when I changed mine the car ran like a champ and my mpg bumped up a bit....
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Old 08-15-2012, 03:22 PM   #8
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Re: RPMs drop and car dies coming to a stop...

Check your egr, could be pulling vacuum at idle.
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Old 08-28-2012, 11:26 PM   #9
mufftang66
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Re: RPMs drop and car dies coming to a stop...

first, thanks for all the suggestions, everyone.

and in the interest of posterity i thought i would update...
car kept stalling at a stop, check engine light came on again, so i got the code read and it was...

P1507, which was Idle Air Control underspeed error - ECM detected an engine speed less than desired.
solutions
1.engine vacuum leak
2.Failed IAC valve
3.open or short in electric
4.air inlet plugged

so i checked for signs of a vacuum leak on the lines, nothing... then i popped $87 for a new IAC valve, installed it this evening and now everything is back to normal. idle is all good and no more stalling or dieing at the stoplight.

I didn't put the IAC mod plate back in, i may do it next time i'm under the hood
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2003 Mach 1 5spd : Zinc Yellow
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1966 Coupe 302 auto : Vintage Burgundy


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Old 08-29-2012, 10:23 PM   #10
FlyMACH1
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Re: RPMs drop and car dies coming to a stop...

I'm on my 3rd IAC valve - 70,000 miles.
The last time it went bad, it made a very loud whistling sound
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Old 08-31-2012, 09:32 PM   #11
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Re: RPMs drop and car dies coming to a stop...

Rarely the case, but you can check the throttle body stop or even un-screw it a tad to increase the idle so it won't stall (worked for me)
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