Idle issue, confused

[Archametes]

My car will sometimes idle at 500 or so and sometimes over 2000 rpm's. I've tried adjusting the BISS screw and that does nothing, I checked the vacuum lines and they seem fine, I cleaned out the throttle body. I replaced the IAC motor already so that's not it. I'm confused I don't want to replace more parts without knowing the real cause. Is the ISC the same as the IAC? I know where the TPS is located and that seems fine. The car will very infrequently throw a CEL code for "throttle control sytem malfuntion"...yeah like that helps me. As if I didn't know that already. If I delete the code the car will run fine for a day or 2 then get worse. It seems to run fine first thing in the morning and then get worse as the day goes on. For example as the ambient temp goes up so does my idle... In the winter it was the opposite, this leads me to think the FIAV is the problem but I don't know for sure because there's no way to check it....


I've searched everywhere I can look on different DSM forum's and just the web in general, and most of the serch links don't work anymore or they are for the wrong generation car... Most of the confusion is that it doesn't just surge, it's a steady high idle.

My car is a 95 Talon TSi AWD, and ANY help would be greatly appreciated.

Thanks, Mike

 

[EvansF]

Search on the forum here, we have like 1000+ thread on bouncy idle.
And we can read always the same thing,
Look at this, this, this bla bla bla

You should find some interesting post, im sure.

 

[super97gst]

My car will sometimes idle at 500 or so and sometimes over 2000 rpm's. I've tried adjusting the BISS screw and that does nothing, I checked the vacuum lines and they seem fine, I cleaned out the throttle body. I replaced the IAC motor already so that's not it. I'm confused I don't want to replace more parts without knowing the real cause. Is the ISC the same as the IAC? I know where the TPS is located and that seems fine. The car will very infrequently throw a CEL code for "throttle control sytem malfuntion"...yeah like that helps me. As if I didn't know that already. If I delete the code the car will run fine for a day or 2 then get worse. It seems to run fine first thing in the morning and then get worse as the day goes on. For example as the ambient temp goes up so does my idle... In the winter it was the opposite, this leads me to think the FIAV is the problem but I don't know for sure because there's no way to check it....


I've searched everywhere I can look on different DSM forum's and just the web in general, and most of the serch links don't work anymore or they are for the wrong generation car... Most of the confusion is that it doesn't just surge, it's a steady high idle.

My car is a 95 Talon TSi AWD, and ANY help would be greatly appreciated.

Thanks, Mike

the trouble code you are getting leads me to believe it could be the TPS throwing random fits. the ecu monitors output voltage from the TPS and determines fuel delivery based on throttle valve angle. the ecu senses the throttle is moving and it can send intermitttent bursts of fuel from the injectors when the TPS is going down. as the other guy said, there's a lot of this. first thing unplug the TPS. then using a multimeter test pins 1 and 4. you should get 3.5-6.5k ohms. this is with the car shut off. then leaving one lead on pin 4 test pins 2 and 4. you roll the throttle from the back side of the throttle body while holding the leads on pins 2 and 4. the reading on your multimeter should change smoothly as you slowly open the throttle plate, staying withing the 3.5-6.5k ohm specs. if not, there's your problem.

 

[Archametes]

But in checking the TPS would it still just idle high? The idle doesn't bounce around or surge or whatever, it's just really high. I can get it down by adjusting the BISS screw everyday but then by mid-day it's back up to 2000 or so RPM's. A friend of mine said it could also be the temp sensor portion of the MAF since it seems to be more with the warmer weather during the day than at night or first thing in the morning... any chance of this? I'd really like to get this figured out asap. Thanks for all your help and i'll do some more searching too...

Thanks, Mike

 

[super97gst]

But in checking the TPS would it still just idle high? The idle doesn't bounce around or surge or whatever, it's just really high. I can get it down by adjusting the BISS screw everyday but then by mid-day it's back up to 2000 or so RPM's. A friend of mine said it could also be the temp sensor portion of the MAF since it seems to be more with the warmer weather during the day than at night or first thing in the morning... any chance of this? I'd really like to get this figured out asap. Thanks for all your help and i'll do some more searching too...

Thanks, Mike

have you tried checking the o-ring on the biss screw?? sometimes the o-ring will get dry rotted and the biss screw will back itself out quite easily because the o-ring can't hold it any more. and yes of course there is a chance of that being the case. the MAF contains 2 sensors, the intake air temp. sensor, and the barometric pressure sensor. the only problem is that if one of those starts giving trouble you have to replace the entire MAF.

 

[Archametes]

OK i pulled the BISS screw out today after i got home from work and noticed the O-ring on the screw does look a little flat on the outside edge, and the screw was coated in black residue( I'm assuming from the previous owner not gapping the spark plugs and the car running rich). As for the MAF my friend ( a mechanic at a Ford dealership who works primarily with turbo diesels) said to take a paperclip bent into a U shape and place it on the thin bar going through the sensor which meaures the ambient temp. If the idle corrects itself then the bar is broken and if you can find where you can solder it. So i figured i'll look into that tomorrow, I got a baseball game to go to tonight.... Thanks for your straight forward answers. This post is on another forum and although 31 people have viewed it no one answered me at all yet... I appreciate it guys.

Thanks, Mike