I have a 1999 ford Taurus sho. And when i do a small rev to either about 2k-3k rpm after I let off the needle drops to under normal idle speed. it never stalls and it quickly catches itself. It has new plugs, coils iac, egr and maf and as far as I know no vacuum leaks. Only thing i can think of is tps sensor but not sure. it never misfires either the intake manifold is clean and the throttle bottle is very clean. I did notcie throttle has a sort of "play" in it but not the wire the bracket.seems it doesn't start opening the throttle till I put my foot down a ways. probably why this is happening but i dunno.

this is not my car but that's pretty much the same exact issue except mine doesn't do it everytime.



This post was edited by Historic on Dec 1 2015 01:56pm

Did you calibrate or reset the IAC when you installed it? Assuming no vac leaks the only thing you haven't addressed is the Map sensor, O2 sensors, and catalytic converter.

yah I had the negative batt term off. As far as i was concerned the iac should calibrate itself. map sensor i dont even know where that is on this motor.

this is what im working with lol lets just say its an interesting challenge to work on.

This post was edited by Historic on Dec 1 2015 05:09pm

On my stuff the IAC and TPS have to be re-zeroed after replacement. Every make is different though. I have to unplug both the tps and iac then key to run for 30 seconds, key off, reconnect.

i'll give that a shot

it was the new IAC valve. luckily i found the old one cleaned it put it in and im pretty sure issue is gone it seemed drive better in stop and go traffic. i'm guessing the lazy spring in the older one doesn't choke air as much? the actual pintle or plastic valves were in the same position but gotta be careful with these new iac valves. i think they react differently to voltages.

They do that is why the factory zero or calibration has to be done. Even then the cheap overseas knock offs are hit and miss.

How do you calibrate the new one? I haven't seen any info where Id have to do this on my car. I remember buying an IAC a long time ago for another car and it made a terribly annoying buzzing hum noise until i got tired of and replaced.

This post was edited by Historic on Dec 2 2015 06:16pm

http://www.taurusclub.com/forum/82-maintenance-repair/79652-reset-computer.html#/forumsite/20664/topics/79652?page=1

Disconnect the battery, wait 5 minutes, they say hold the brake, i prefer touching the battery cables together. That will clear the learned idle trims. Start the car with the A/C off, don't touch the gas or brake, let it idle for 15 minutes. This is best done as a cold start.

they keep saying in the sho forums that the gen 3 sho doesn't need it's iac calibrated. i'll try anyway even tho the old one works better kinda want the new one to work if it's not ata fault.

This post was edited by Historic on Dec 2 2015 09:05pm