loss of power at full acceleration??

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

Or for a nicer scanner see http://www.midwayautosupply.com/detailedproductdescription.asp?3829 – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

i have the same prob i just installed a set of gt40p heads on mine and when you stomp the gas it kinda feels like a turbo car it has some lag. I have been messin with the timing and it seems to change it. Have you installed anything lately or messed with the timing.

Check the plugs too, I've seen fouled plugs play tricks before. Make sure its running on all 7 cylinders too lol, its happened before that a plug wire has melted to a header.

a1yola said:

I've ran a code test and it said something about the IAC valve. I replaced it, and the code is still there. Not sure why though Can the IAC be causing this problem??

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what year is your vehicle? IIRC, there is not (at least for 86-93) a code for IAC. what code did you get?

Check the TPS, make sure it climbs in voltage consistantly as the throttle increases. Should be from .9 at idle and about mid 4's at WOT in voltage from the signal wire. If not that, check fuel pressure and MAF.

I believe that 12 and 13 would relate to the IAC.

HISSIN50 said:

I believe that 12 and 13 would relate to the IAC.

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yep, i forgot about those.

12 and 13 are for idle. sometimes caused by a clogged or faulty IAC, most of the time the idle is not in the proper range. since you've replaced the IAC already, you might want to make sure your idle is set properly. also make sure your throttlebody plate moves freely and is not sticking at all.