UPDATE: Idle Speed Problem

[mo_dingo]

1995 Mustang GT, stock except k&n air filter.

Well, after some wrench turning on my car, my idle speed is still out of whack. Here is a quick briefing on my problem.

Idle speed varies anywhere between 2000 - 2800 rpm's.

Before this problem, my idle speed was a little low (around 500 rpm's). So I removed the IAC valve, soaked it in carb cleaner, and put it back on. I then cleaned my k&n air filter. I put everything back on, allowed 3 hours for the oil to dry in the filter, and started the car. The 2800 idle rpm problem started then.

So, today I bought a brand new IAC valve w/ gasket. I installed it, and it changed nothing. I checked the voltage, and it read about 11 volts, which means the PCM is giving the correct signal (acceptable range is 10 - 12 volts).

Tomorrow I am going to remove the IAC, and have someone cycle the ignition on/off while I watch the new IAC valve to ensure it's working properly.

Assuming the new IAC is working, what could cause the problem? There are no vacuum leaks where the IAC & TPS meet the Throttle Body.

Could the TPS be screwing things up? I thought the IAC valve was the only thing that determines the idle speed. If anyone could point me to some technical data about the TPS and IAC valve, it would be appreciated.

BTW, I tried turning the screw on the TB and I could only increase the idle speed further (turning counter-clockwise). I turned it clockwise as much as possible (to decrease), but it won't go any more.

Anyone have any ideas?

BTW, which wires do I need to probe on the TPS to check it's voltage? What should I read when the throttle is closed? At WOT?

I am getting close to taking it to a frickin' mechanic. This is really irritating!

Thanks for the help!!!!
Scott

 

[mytight95]

I actually had the screw on my original factory throttle body strip out about half way up the threads, not allowing it to be adjusted down any further, this could be your prob. It the scerwon yours botoming out when you turn it all the way clockwise?

i think that this is your problem!

let me know, you can try and take a plug and plug the hole where the Iac goes into the TB behind the butterfly and then adjust the idle via the voltage screw. and see what that does, if it goes down the screw isn't all the way down on the TB

 

[mytight95]

You also need to check the voltage on the TPS sensor-to do this you take a voltmeter and check the volts on the middle wire(there are three) and then get a good ground, your voltage should be btween ..950 and .999 most likely just slightly less than one volt my sweet spot seems to be around .992

 

[mo_dingo]

You also need to check the voltage on the TPS sensor-to do this you take a voltmeter and check the volts on the middle wire(there are three) and then get a good ground, your voltage should be btween ..950 and .999 most likely just slightly less than one volt my sweet spot seems to be around .992

Alright, so use the ground on the battery terminal, and the hot wire on the middle wire. Sounds good.

But what does the TPS have to do with the IAC valve. The TPS tells the computer what position the butterfly valve is, correct? How would that affect the IAC valve.

BTW, I checked the voltage at the IAC valve, and it reads 11 volts, which is within normal specs.

I will check the voltage at the TPS, remove the IAC valve and make sure it's working properly. Sounds like a plan of attack.

The idle screw can unscrew (turn counter-clockwise) for a very long time. But that makes the idle higher.

When I turn it clockwise, it turns with ease until it completely stops. I do not believe it is stripped.

I will try the TPS and the IAC again and post back.
Thanks!!!
Scott

 

[DavidF]

I also had an idle problem with my SN95. Every day the idle seamed to get higher and higher up to about 2k. I tried all the thing you’re supposed too but no luck. To drive it I ended up blanking off the IAC and got the car to idle. I drove it like that for a few months until I had a problem with the motor cutting off while driving on the freeway. Only then did my computer come up with an error. It said the PIP was bad. I replaced it and then decided to try to put the IAC back on. And guess what? Everything was back in working order.

 

[Rootus]

I would bet it's not the TPS. The TPS on a 94/95 is baselined by the EEC when you start the car, and it's not designed to be adjusted. If it is far enough out of whack that the EEC can't deal with it, then you'll get a MIL.

I like DavidF's idea -- a lot of people with 94/95's seem to be having ignition malfunctions lately, it may be that we're reaching the average lifespan for the stock equipment. That's what I would check.

Dave

 

[timk]

david, PIP?

 

[DavidF]

david, PIP?

Yeah, it’s in the distributor. It’s the pick up that tells the computer where the rotor is, kinda like the “points” in an older system. “profile ignition pick-up” Sometimes called “hall effect sensor”.

 

[mo_dingo]

Hmmm. Very interesting. Thanks for the info Dave. I thought the TPS had nothing to do with it.

I am having trouble finding the PIP sensor on autozone's website. What would it be called??

I will check the IAC tonight and make sure it's responding to voltage. If it is, I guess I will get a new PIP.
Scott

 

[mytight95]

I wasn't thinking that something was wrong witht he tps i just figured if the voltage was too high then the screw ont he throttle body that moves the butterfly itself along with the tps, was screwed in too far and allowing too much air in through the tb itself and not even through the IAC


just a thought., I've been wrong before but just trying to help

jason

 

[mo_dingo]

No worries. Your post helped me rule out the TPS as the problem. You actually helped!!!

I didn't mean to sound condescending. I apologize if I did. Damn internet. Can't hear tone of voice!!!!

I found the following things related to the dist. Which is the PIP???

Stator - Pick up Coil
Control Module

Does the Stator = PIP??????
Scott

 

[Rootus]

Does the Stator = PIP??????

Yes indeed.

Dave

 

[mo_dingo]

Yes indeed.

Dave

Cool. Could the PIP cause my high idle speeds? I figured it would make the car run rough, not make the idle speed jump! Please inform me!!!!!

If it can increase the idle speeds, I will replace it if the IAC is functioning fine. I will know by tonight!
Scott

 

[mytight95]

No problem --i just don't want to come off as a know it all because I am not by far with these damn tempermental cars i have learned to keep mine in tune etc. keep a check on it every week or two.


jason

 

[sldghmr]

When my PIP went out on me it just caused a rough idle not high though. It's a PITA to change, because not only do you have to pull the distributor, the shaft has to come off and the gear at the bottom. I pulled my distributor and took the whole thing to local gas station and they changed it for $5. Of course that was well before my idle decided to climb to 3000.

 

[mytight95]

So if you take the dist. out of the car a shop will change it for you for a descent price.

i think i need to replace mine.

please explain more about this pip thing

thanks

 

[mo_dingo]

UPDATE: I removed the IAC valve from the TB, but still kept the wires connected. When I turned the key to ACC, the IAC valve didnt move at all. When I was holding it, cycling the ignition on and off, I felt something move. But the rubber plunger and spring did not move when I cycled the ignition on/off. BTW, I am still reading 11V on the plug when ignition is on, so I know I am getting the correct signal still.

I then swapped the new IAC valve for a new one. Same story. Didn't move, but I felt something.

So I decided to install it just in case. THE IDLE RETURNED TO NORMAL!!!!

I WAS LIKE WAHOO!!! I disconnected the battery for 20 minutes, to reset the computer.

I then went out there to leave, and the idle problem came back! WTF?????

What is going on? I am so confused??? What could I have done to get it to work initially, but then fail later????

Your help is appreciated as usual!

I don't think it's the PIP, becuase my idle quality was perfect when it went back to normal.

Oh, almost forgot. When I start the car, with the IAC valve connected, idle is high, then disconnect the wire plug, the idle REMAINS THE SAME!!! What is going on????
Scott

 

[mytight95]

MAN you are having somer real issues with that thing, did you ever check the voltage on the tps. was it normal? not thinking it is the tps but maybe the tb oopen too much. I would take the tb off and take a good look at everything, another thing i would do is once i got everything revonnected i would take loose the IAT sensor and see if the idle changed, i know this sounds funny but i can unplug it and my whole idle changes.

Maybe we can help you getthis thing worked out eventually.


jason

 

[mo_dingo]

No, I haven't checked the voltage yet. I will soon.

Does anyone have any technical data on this sensor? I really need to get the IAC valve out of the equation.

My uncle gave me some ideas. He said to try using two jumper wires and use that to connect the IAC valve to it's wire connecter, instead of the factory plug. When I disconnect the wire plug, nothing happens. So maybe it's not getting a good connection. That's step #1.

#2 is to run compressed air through the two holes the the TB where the IAC plugs into. If the IAC valve is operated by both vacuum and electricity, then "vacuum" might be my problem. I sprayed an arse load of carb cleaner into the motor. Maybe there is some carbon blocking the hole now because I knocked some carbon loose.

The hose to circulate oil fumes through the motor goes right into the air tube. So I am sure there is at least "some" buildup.

#3 is to remove the TB and check everything.

There appears to be a seal between the TB and the upper intake manifold. Can I re-use the existing seal, or should I replace it? Where would I get one? The haynes manual doesn't say anything about it.
Scott

 

[mytight95]

as long as you don't have any tears in it i would say to reuse it b/c they seem to be hard to find at local parts stores.

well when you check the voltage and that is not it i will try and help you to figure out something else that may be causing this


jason