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sputter from engine when coming down from idle

tomtoc

tomtoc

2,049
68
Springfield, MO
when i'm next to a wall, or can hear the engine really well and i rev it a little - it sort of sputters or pops on its way back to idle.

i'll rev it to 2k rpm and it sounds normal down to about 1,000 and it sort of pops/sputters/coughs back down to 800. what would cause that?

timiing? spark plugs? something like that?
 
smokey

smokey

Hitech hillbilly
Staff member
13,257
706
Garrett Co. Maryland
My guess is that the idle air control is activating to adjust the idle. this sounds normal for a older engine.
the IAC stick alittle as they get older and that is what you are hearing.
 
smokey

smokey

Hitech hillbilly
Staff member
13,257
706
Garrett Co. Maryland
Yes it could cause the problems from the other post.
Cleaning the IAC is a 50/50 shot. some times it helps some times it doesn't. A regular choke and carb cleaner is all you need to clean it out. then spray it with a light oil like PB blaster or wd40 before putting it back on.
 
Skandocious

Skandocious

Post Whores Make Me Sick
19,076
655
California
The IAC is used to control engine idle speed... If your truck is idling normally then I don't think there's anything wrong with the IAC. Is it idling normally?
 
smokey

smokey

Hitech hillbilly
Staff member
13,257
706
Garrett Co. Maryland
tomtoc said:
- it sort of sputters or pops on its way back to idle.

i'll rev it to 2k rpm and it sounds normal down to about 1,000 and it sort of pops/sputters/coughs back down to 800.
Click to expand...

Skandocious said:
The IAC is used to control engine idle speed... If your truck is idling normally then I don't think there's anything wrong with the IAC. Is it idling normally?
Click to expand...

If the IAC is sticking and not keeping up it can cause these problems it controls the air. the IAC will kick in at about 1000rpms and can make it sputter if it is hanging up.
 
Skandocious

Skandocious

Post Whores Make Me Sick
19,076
655
California
I suppose that could be correct... But the symptoms I've always seen with a dirty/bad IAC almost ALWAYS included irregular idle.

I suppose it wouldn't hurt to clean it and see. The 4.9L IAC appears to be cleanable, while the others are not.

Ford said:
The idle air control valve (IAC valve) (9F715) on the 5.0L, 5.8L and 7.5L engines is of a sludge-resistant design and should not be cleaned; otherwise damage may occur.
Click to expand...
 
smokey

smokey

Hitech hillbilly
Staff member
13,257
706
Garrett Co. Maryland
you are correct in that they normally cause a irregular idle. sticking can causing a high idle or a stall. But before going all the way out I have seen alot of them start acting up and causing this same problem.
Cleaning it shouldn't hurt it but I doubt it will help. cleaning seldom helps them for long if at all.
 
Skandocious

Skandocious

Post Whores Make Me Sick
19,076
655
California
Yeah try cleaning the IAC like Randy said see if it makes any difference-- that could very be the problem, or at least lead you in the right direction.
 

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