Speed Density idle issues?

88 Fox GT

Active Member
Nov 18, 2002
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Iowa
Do speed density cars usually have idle issues? My '88 GT will not idle every once in awhile and just wants to die unless on the gas. It only happens a little, not all the time, no matter the temperature of the engine or air. At first I thought it was because I didn't have any O2 sensors (they were rotten), but I installed my new ones last night and it's still doing it. Does it have anything to do with the MAP sensor or does something like the IAB need to be cleaned out?
 
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Mine did that a lot too.. mostly when I started it up after not running it for an hour or more. Engine temp. didn't matter. I removed my IAC and cleaned that heck out of it, and although my idle is a little bit higher now, it hasn't done the stalling thing since.

Might be something else, but never hurts to clean your IAC anyway.
 
sgarlic said:
Mine did that a lot too.. mostly when I started it up after not running it for an hour or more. Engine temp. didn't matter. I removed my IAC and cleaned that heck out of it, and although my idle is a little bit higher now, it hasn't done the stalling thing since.

Might be something else, but never hurts to clean your IAC anyway.
That seems to be the way mine is as well. After it has been sitting for a little while. I will try cleaning the IAC and see how it does.
 
Yes, speed density cars are known to have more of an idle problem than mass air cars. I think the difference is that a speed density car uses only the preprogrammed info inside the computer to tell it what to inject and when, based on general info from the throttle position, manifold vacuum, air temperature and what have you. But the mass air cars are using that info PLUS measuring how much air is actually being sucked into the motor, which gives the computer a much more accurate picture of how much fuel it needs to inject. And that difference allows it to compensate for changes in the engine, such as heads, cams, etc. That's why speed density cars fall down when you do mods on them -- they think that the car is stock, and don't have any way to tell otherwise. But you should still go down the checklist of possible problems contained in the "sticky" about surging idle issues at the top of this tech forum list. It contains a pretty comprehensive list of things that can affect your idle.
 
First thing I will try is cleaning the IAC. Next thing will be to check for vacuum leaks and such. I think I still have some unhooked lines when I removed the smog pump. If none of that works, I will swap MAP sensors with my '87 F150 to see if that cures it. If so, I will buy a new MAP sensor. Thanks for the help.
 
When mine was SD I found a vac leak EVERY time an idle issue would arise..check several times..i found mine just inside the passenger fenderwell..found it after the sixth time going over the whole vac system..don't give up.