Idle Problem

[Awt2]

Hello,

I am having a slight problem with my 97 Cobra idleing. Every so often, it will drop down to 200 or so RPM, and act like it is going to stall. Once today, it actually dropped down to 50rpm and died on me. I wasn't moving, the car was in neutral and I had the clutch in. I gave it gas, but it didn't respond much to it, just stalled.

I'm hearing from my Auto-shop teacher that the problem is linked to my IAC, is that true? Do I need a new one or can it be repaired?

The car has no mods done to it engine wise.. 4:10's being the only major upgrade.

 

[CzchMex]

I have the same issue. It happens so randomly that I can't link it to anything. But I do have my AC running everytime this happens. Not sure this is tied into it.

I haven't cleaned my IAC yet, but something points me to that being a big culprit in this problem

 

[SVT Pille]

Leaning towards your IAC or TPS, more than likely it needs to be cleaned. If that doesn't fix it just buy a new one, they're cheap.

 

[encasedmetal]

check to see what your TPS voltage is (a handheld scanner can do this) and clean your IAC

 

[mwolson]

TPS voltage doesn't matter much with 96s and up. The PCM learns the voltages at idle and WOT, and remembers what the voltages are. That is why it is better to log TP_Relative, rather than TP_Absolute when trying to debug issues like this.

It is an issue for older cars, however.

 

[Beerdog80]

I have the same issue. It happens so randomly that I can't link it to anything. But I do have my AC running everytime this happens. Not sure this is tied into it.

I haven't cleaned my IAC yet, but something points me to that being a big culprit in this problem

Mine did the same thing. Replaced the IAC and that cured the problem.

 

[encasedmetal]

TPS voltage doesn't matter much with 96s and up. The PCM learns the voltages at idle and WOT, and remembers what the voltages are. That is why it is better to log TP_Relative, rather than TP_Absolute when trying to debug issues like this.

It is an issue for older cars, however.

I gotta beg to differ with you on this Mark. it's made a massive difference on every setup I've had. especially using aftermarket TB. my idle has never settled unless my TPS voltage/position is dead on and I set my TB position screw from there (all of this done with the IAC unplugged)

 

[Awt2]

Alright, ill look into cleaning my IAC then. I'll do it tommarow in my shop class and report back

 

[mwolson]

I gotta beg to differ with you on this Mark. it's made a massive difference on every setup I've had. especially using aftermarket TB. my idle has never settled unless my TPS voltage/position is dead on and I set my TB position screw from there (all of this done with the IAC unplugged)

Per my SCT dealer training, a better way is to tweak the TB idle stop screw until your ISC_Duty_Cycle is about 35%. Then you tweak the IAC transfer function until the ISC integrator is running around 0. At that point, the PCM will be able to control the idle, assuming you have no other mechanical problems.

The PCM needs to have anough range in IACV duty cycle to go where it needs to go.

FYI, the PCM only does coarse control of idle with the IACV. It does fine control of idle with spark. (Make sure the spark source is a steady 9 at idle.)

I haven't run across a 96+ car that hasn't worked well with this process, unless there were other problems, such as vacuum leaks, or bad IACVs.

That said, I haven't worked with a lot of aftermarket TBs. The stock TBs have all done well with this process.

But if your process works too, then that is cool.

 

[Beerdog80]

Thought I would post what the inside of a dirty IAC looks like.

and without the rubber...

 

[STAMPEDE3]

TPS voltage doesn't matter much with 96s and up. The PCM learns the voltages at idle and WOT, and remembers what the voltages are. That is why it is better to log TP_Relative, rather than TP_Absolute when trying to debug issues like this.

It is an issue for older cars, however.

Yes it is reletive and learns however Per Ford it also must be within a certain range so it does matter.

If it is so for out of the range and remembers that voltage it basicly knows that something is not right and will not 0 itself to that point.

 

[Njc0las]

Leak in the pcv valve rubber somewhere? Maybe iac? Other vacuum leak?