Uneven EFI idle

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May 6, 2004 | 07:00 PM

nickmobile67

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From: East Coast

Uneven EFI idle

My 86 F150 has EFI 302 and manual tranny. It also has an MSD ignition box and coil. If you leave it sit there and idle on regular slow speed, the idle will drop by about 100 or 200 rpm's. It isn't loading up with fuel, it just can't decide where it wants to be. It dosn't raise above where it idles good, it just drops and then decides that the speed is too low and raises back to where it should be. It dosn't stall out, but it is annoying. It has a new fuel filter, and I usually throw a botttle of injector cleaner in it at every oil change. The truck had sat for a while, but it's been my daily driver for the last few years. It is very dependable. Most on it is original unless I changed it, so I can tell you about most of it.

I was thinking maybe the IAC valve. Maybe it could be the EGR valve, or a clogged injector? What should I do?

May 6, 2004 | 07:57 PM

The Weezle

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From: Clinton

Mind of its own idle

cleaning the IAT is a good place to start make sure you clean the passages really good as well........ I remmember reading a thread on this forum about checking the Idle adjustment can't remember the proceedure but it involved diconnecting the battery and doing something else and reconnectiong the battery and it should idle properly try doing a search on this topic i'm sure you will find it. also buy some throttle body cleaner follow directions I think your throttle body is coated with a protective material and you have to make sure that the cleaner won't harm the coating clean the throttle body as well as the IAT passages with it Check haynes manual and do a check on the throttle positioning sensor if all else fails Map sensor check vac line going to it do the simple stuff first hope this helps I think the IAT will be the problem however ....Good Luck

May 6, 2004 | 08:02 PM

TUFFY

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From: kirksville mo

Yes i would have to agree the iat is not that hard to replace mine did the same thing and changing the Iat solved the problem. Dave

May 6, 2004 | 08:15 PM

nickmobile67

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From: East Coast

Ok, I'll look into that. IAT, that the same as a IAC right? I'd assume about $25-50 new?

I have a set of ford shop manuals for my truck. I'll have to do some research in there. I don't think it gives much in the way of troubleshooting though.

May 6, 2004 | 09:04 PM

bremen242

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From: GANS

if you are having idling trouble, most people point to the IAC valve on the TB. Try cleaning it first....

May 7, 2004 | 08:18 PM

nickmobile67

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From: East Coast

Ok, I looked in my manual. I see the IAT is different from the IAC. It reffers to the IAc as the Throttle air bypass valve, and the IAT (Intake Air Temp) as the ACT (Air Charge Temp) sensor. Anyway, what seems more likely?

I see the IAC is two piece. You can pull the whole thing of the TB, but you need to change the gasket, or you can take it apart with 2 screws. What is the best way to clean it? and if I need to take it off, can I get a new gasket without buying the whole valve?

ACT looks like it would be a real pita to get to, on the front of the lower intake between the #5 and 6 injector.

May 7, 2004 | 09:36 PM

Beast12

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From: Sarnia, Ontario, CANADA!

Quote:

Originally Posted by nickmobile67

I see the IAC is two piece. You can pull the whole thing of the TB, but you need to change the gasket, or you can take it apart with 2 screws. What is the best way to clean it? and if I need to take it off, can I get a new gasket without buying the whole valve?

You don't NEED to change the gasket as long as you can get the old one off without wrecking it. Just be careful. When you have it off, take some throttle body cleaner (not carb cleaner) and spray it inside and swish it around. Just keep spraying and swishing (maybe use a toothbrush if it is really dirty) until it is pretty clean. Let it dry out (shouldn't take long) then put it back together.

Make sure you disconnect the battery for at least 10-15 minutes then drive it around when fixed so it can "relearn" the idle. Good luck!

-Matt