GEORGIA GT

Have a few questions about my 1997 read several pages and threads and didn't see my same problem so here goes. Have replaced the IAC, the black evap sensor the round purge valve cleaned the MAF very carefully. Previous owner cleaned the plenum and throttle body. What the car is doing is when I come to a stop it will idle around 1500 for 10-30 seconds then will drop down around 600-700 and stay there. Between shifts the rpm's will stay up and not fall also when I let off going down a grade it doesn't always slow down sometimes it will sometimes it won't. Any help or ideas will be greatly appreciated.

KB00GT

Sometimes a vaccum leak will cause idle surges or the idle to not drop when letting off the throttle. Also not to be mean i have no idea of your experience level, but is it a manual? A manual will not lose RPM going downhill if it is still in gear?

96t-bird

Hi, when you cleaned the TB. Did you check to make sure it was closing completely?Is your return spring weak on the TB? Did you also check and clean out the EGR valve? All the vacuum lines connected to the TB?Just some ideas for you to check out first.

crysalis_01

Is there a CEL on? If so, my little sister had a similar, almost exact, issue with her '02 SVT Focus. After checking things like the IAC, which needed substantial cleaning, TB, and TBPS, it turned out to be her upstream O² sensor was malfunctioning and causing the "odd" idle. Swapped out the sensor and BAM problem solved

stevednmc

Im almost certain that this is an IAC issue. You should REPLACE the Idle Air control valve. Do not waste time cleaning it, Ford recommends replacement and says its a non-serviceable part. If you do attempt to clean it t will likely be a temporary fix.

Keep in mind that what the car is doing is what its supposed to do, albeit the 1500 rpms are too high. The IAC keeps the rpms a little high when coasting and slowing down to keep the power steering pump speed up for the brakes, there is no vacuum booster on these cars, they are boosted off the power steering.

Also, when replacing try and replace with a motorcraft part. Ive seen people replace the IAC from an auto parts store several times in a row and having issues until they got an OEM part.

GEORGIA GT

Thanks for the replies I'm going to test the TPS voltage tomm and replace the vacume lines on the evap thats the only code I have right now P1443 I have replaced the purge valve and the black sensor on the evap. The o2 sensors are new I was not the one who cleaned the TB and the return spring is good. I tried cleaning the IAC already did not help so I will reoplace it.

rbowmar

I'm not sure you have a problem. Both my 2003 and 2005 show exactly the same performance. I don't know if that mode of operation extends back to the age of your car but it's not hurting anything and spending a lot of time fix what is standard performance these days may not be the best investment of your modification budget.
I found another bit of odd behavior while checking this out. while coasting down a long hill. holding the clutch or shifting into neutral never drops the engine speed down to below 1000 rpm until I have completely stopped and waited the requisite 30 seconds!

GEORGIA GT

If it's normal I would rather spend the money on mods a motorcraft IAC will run $107 here.

stevednmc

It is normal if it hangs at around 1000 rpm or so then after a few seconds drops to normal idle speeds. If its hanging at 1500 rpm, it is too much. Next time you drive it just check and make sure. FYI there is a mod to end the hanging RPM madness once and for all, should you choose..https://mustangforums.com/forum/4-6l...ging-rpms.html

wifes pony

yes sir, if the hanging revs bother you, like they did me. let that be your 1st mod. i elected to go with the copper cap, in the hose. be sure to start small with the hole. U can always, adjust. in addition, doing that doesnt hurt the car at all, does it?