Cutting out at idle
Thread Starter
Drifting
Joined: Jun 2002
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From: Iowa
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Cutting out at idle
What would cause an intermittant condition that sounds like a sparkplug is not firing all of the time at idle? Sometimes it occurs once in a while, and other times it may do it 3 or 4 times in a row in rapid succession, which almost causes the motor to stall. If I hold the brake on and rev it up a little, the "miss" goes away.
At cruising speeds and at WOT, it runs just fine. I checked a few plugs and they are gapped a little closer than I feel they should be (.030), but I wouldn't think that would be causing the "miss" I am feeling. Plug wires are nearly brand new, so I wouldn't suspect them either. And no codes are coming up.
Any ideas what to look for? Oh, btw, it's a 96 LT1 with A4.
At cruising speeds and at WOT, it runs just fine. I checked a few plugs and they are gapped a little closer than I feel they should be (.030), but I wouldn't think that would be causing the "miss" I am feeling. Plug wires are nearly brand new, so I wouldn't suspect them either. And no codes are coming up.
Any ideas what to look for? Oh, btw, it's a 96 LT1 with A4.
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: Cutting out at idle (MagikDraggin)
A miss will be plugs, wires, opti or PCM.
A regular miss will be wires or plugs.
If it's the opti, normally (if there is any such concept with regards to the opti) it will be random, it will get worse over time, it will start missing at higher RPMs then slowly deteriorate down the RPM range.
PCM is a last resort after everything else is eliminated.
How many miles on the car and on the opti? Did you get the engine compartment wet recently? Sometimes these types of misses will clear up when the component dries. Sometimes it toasts the opti (not often with the later opti, but it happens).
A regular miss will be wires or plugs.
If it's the opti, normally (if there is any such concept with regards to the opti) it will be random, it will get worse over time, it will start missing at higher RPMs then slowly deteriorate down the RPM range.
PCM is a last resort after everything else is eliminated.
How many miles on the car and on the opti? Did you get the engine compartment wet recently? Sometimes these types of misses will clear up when the component dries. Sometimes it toasts the opti (not often with the later opti, but it happens).
Thread Starter
Drifting
Joined: Jun 2002
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From: Iowa
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Re: Cutting out at idle (John Row)
64k on the motor. The opti is original and has never (to my knowledge) gotten wet. Water pump was changed @ 47k. And yes it is random....not like a cracked or shorted plug wire, although once in a while it will missfire in rapid succession as though more than one plug was not firing. Then it will smooth out for a few seconds, then miss once, then once again, then two in a row and smooth out, and then do it all over again. But once I put a load on it, it quits.
I have not noticed any hi speed miss. If it is the ecm, does that mean the whole units must be changed, or is there something in it which can be serviced? Are these things expensive (like the opti is)?
[Modified by MagikDraggin, 11:01 AM 6/23/2003]
I have not noticed any hi speed miss. If it is the ecm, does that mean the whole units must be changed, or is there something in it which can be serviced? Are these things expensive (like the opti is)?
[Modified by MagikDraggin, 11:01 AM 6/23/2003]
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: Cutting out at idle (MagikDraggin)
It does sound like an Opti. Fortunately, for a 96 they are about $200 complete.
You might try to find a shop with a TECH II analyser to see if you can isolate any particular cylinder as the culprit. If so, then plugs and wires. If not think opti. The shop might charge you for an hour of time. It might be worth it.
Once you give it gas, you probably still have a miss, but if it is the opti it would be random enough as to be unnoticable at higher RPM.
Last time my opti went out I was able to isolate the problem by pulling the air supply line (air line from the intake line just behind the MAF) and squirting compressed air into it. I used one of those cans of air used to blow out keyboards. One squirt, idle smoothed right out for a minute or so, then miss returned. Another squirt, smooth sailing for another minute.
I wouldn't worry about the ECM, yet. It's pretty rare that they go bad. Yes, they are expensive, something like $600-$800. All one piece. You might be able to find a used one.
If it's the opti, you can do it yourself and save a bunch of $$$.
You might try to find a shop with a TECH II analyser to see if you can isolate any particular cylinder as the culprit. If so, then plugs and wires. If not think opti. The shop might charge you for an hour of time. It might be worth it.
Once you give it gas, you probably still have a miss, but if it is the opti it would be random enough as to be unnoticable at higher RPM.
Last time my opti went out I was able to isolate the problem by pulling the air supply line (air line from the intake line just behind the MAF) and squirting compressed air into it. I used one of those cans of air used to blow out keyboards. One squirt, idle smoothed right out for a minute or so, then miss returned. Another squirt, smooth sailing for another minute.
I wouldn't worry about the ECM, yet. It's pretty rare that they go bad. Yes, they are expensive, something like $600-$800. All one piece. You might be able to find a used one.
If it's the opti, you can do it yourself and save a bunch of $$$.
Thread Starter
Drifting
Joined: Jun 2002
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From: Iowa
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Re: Cutting out at idle (John Row)
Just what I need.....more money down the tube. I guess that's the price that one must pay for the priviledge of owning a piece of American legend.
Thanks much for the info. One thing though, what exactly would blowing air into that hose do for causing the rough idle to smooth out, even if only temporarily? Just curious, that's all.
Thanks much for the info. One thing though, what exactly would blowing air into that hose do for causing the rough idle to smooth out, even if only temporarily? Just curious, that's all.
Melting Slicks
Joined: May 2001
Posts: 2,143
Likes: 7
From: San Diego CA
Re: Cutting out at idle (MagikDraggin)
I don't know for sure. It might have cooled down the internals just enough to function properly for a short period of time. Mine was only missbehaving when it was hot.
Drifting
Joined: Nov 2002
Posts: 1,365
Likes: 3
From: Huntsville AL
Re: Cutting out at idle (MagikDraggin)
Another possibility is that your IAC valve needs cleaning or replacing. I think I have this problem. Every now and then (and it is very random), the car just does not want to idle. It will cough and sputter and seem like it's going to stall. This is usually after I have been driving for awhile and then come to a stop. It's fine at any speed other than idle. If I give it a little gas, it clears up. A friend with a rustang had these symptoms, too. He cleaned his IAC valve and it fixed it. That would be cheaper and easier than an opti replacement. At your mileage, probably needs cleaning at least.
Thread Starter
Drifting
Joined: Jun 2002
Posts: 1,847
Likes: 1
From: Iowa
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Re: Cutting out at idle (HammerDown)
I just gotta get me a service manual! Excuse the dumb question, but what does IAC mean and where is it located?
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