Idles weird?

Venom95 · Feb 17, 2007

ok..just recently bought a 95 Cobra...car has a B cam in it, otherwise stock. I did a complete tune-up on it after I bought it(plugs, wires, cap, rotor, fuel filter, cleaned the MAS, the IAC, replaced a bad TPS, and set timing to 13*) Car will idle up when you press in the clutch..doesnt matter at what speed you are running or even idleing it hangs at 1600 for several seconds and then slowly will work itself down to between 800 and 1000. Any ideas what to check? I am thinking I might have a bad IAC, just want some advice before I go buy one. Thanks!

WHTCONVT94 · Feb 17, 2007

I have the same problem with my 94, It has the b303 cam in a GT-40 create motor.I have replaced everything tps,iac, masair,had it tune by Delk Performance still has hi idel till you come to a complete stop. Have been told that it is the speed sencor in the computer. sorry not much help. if you figer it out drop my a line. go to www.delkperformance.com

JERSEYTHUNDER · Feb 17, 2007

The fuel injected Mustang uses a small motor/valve assembly that allows a specific amount of air to enter the engine to control it's idle. This valve is comonly called the idle motor, the IAC (idle air control) or the IAB (Idle air bypass). When your car is new the IAC works remarkably well. The problem arises when the car gets some miles on it (usually 75K+) and carbon fouling takes its toll.
What happens is dirt, excess air filter oil, and most notably carbon gunks up the IAC valve and doesn't allow it to either open or close properly. This can cause an really high idle, a lumpy/surging idle or no idle at all. The solution is to either replace or clean the IAC. Obviously we are going to do the later and here is how.

1. What is needed?
- 8mm or 5/16 socket and ratchet
- Can of Carburetor/throttle body cleaner (MAKE SURE IT IS SAFE FOR TEFLON-COATED THROTTLE BODIES !!!)

2. Locating the IAC valve:
Depending on the year of your Mustang the IAC can be in a few different locations.
- On 5.0L Fox body cars the IAC is bolted to the side of the throttle body.
- On SN-95 cars it is bolted to the intake manifold
- On 4.6L DOHC and SOHC engines the IAC is located on the upper intake manifold.
In reality once you know what one looks like you should have no trouble finding yours. They all look basically the same except pre-94 cars were made of metal and are silver, 94-up cars are black plastic.

3. Removing the IAC:
This part, like the rest of the steps in this article, is simple. The IAC has an electrical plug that needs to be disconnected Then all you have to do is remove the two 8mm-5/16" bolts that hold the IAC to the throttle body or intake. Watch out for the IAC motor to throttle body gasket, don't lose it!

4. Cleaning:
Next all you do is use the carb cleaner to clean the carbon out of both of the holes in the IAC valve and both of the holes in the intake/throttle body.

5. Putting it back together:
Yet another self explanatory step. Put the IAC in place and install/tighten the 8mm bolts. Make sure you don't forget to reinstall the gasket.

6. Fire her up!
Finally you need to start the car and let it run for a few minutes to burn any leftover carb cleaner in the intake. You may have to crank the engine a little more than normal to start it for the first time and don't worry about the white puff of smoke you see coming from the exhaust because again it's just the carb cleaner.

you can try cleaning the MAF also.....

IF YOU ARE NOT SURE ON WHAT YOU ARE DOING.....THEN DON'T DO IT.....get more info or someone that does know...
don't rush, take your time, and get all the info you can!!!

Win · Feb 17, 2007

i have a New Ford IAC for a 94-95 gt i am pretty sure it's identical to the one of the Cobra

JERSEYTHUNDER · Feb 17, 2007

i am pretty sure.............. :dunno:

JT

Win · Feb 17, 2007

http://www.muscularmustangs.com/iac.php

Yeah i figured they were the same i just had to make sure.

JERSEYTHUNDER · Feb 17, 2007

purplehaze · Feb 21, 2007

man i just recently had a ecam installed along with a 70mm throttle body and trick flow intake!my car has a bouncing effect idle- bounces to bout 1400-1600 then works it way down and when i at a steady speed this is a small jerking movement. hard to notice but its there. what are any suggestions on what to check for!! thanks.

ryclef331 · Feb 21, 2007

purplehaze said:
man i just recently had a ecam installed along with a 70mm throttle body and trick flow intake!my car has a bouncing effect idle- bounces to bout 1400-1600 then works it way down and when i at a steady speed this is a small jerking movement. hard to notice but its there. what are any suggestions on what to check for!! thanks.

YOU need a tune. That Bucking is the ECU being confused by the cam. The part throttle fuel tables are all outta whack with that cam.

As for the hanging idle until you stop, this is called a dashpot function. The ECU cracks the IAC open a bit more to let the engine hang bit inbetween shifts to make shifting smoother. I don't remember which pin it is going to ecu but you can actually cut it and it will eliminate this. ALSO, even though you may have thrown a new TPS on there, did you check the voltage? Anyone that tells you a 94-95 ECU does it every start up is full of shit. PERIOD. Set the TPS Voltage. An incorrect reading can cause a hanging idle as well.

Venom95 · Feb 22, 2007

I checked the TPS voltage it was at .95, I set it at .99. I also went through the base idle settings and the car seems to idle much better...It did however try and cut off on me a couple of times. I also noticed a hex nut on top of the trhrottle body...What does that control? Mixture? Thanks, sorry for the newb questions...

Win · Feb 22, 2007

does it have a rubber stopper in there if it does thats the Idle setting screw

Venom95 · Feb 22, 2007

thats it.....does it just fine tune the idling? I used the stop screw on the other side to adjust the base idle..

purplehaze · Feb 26, 2007

what would the tuning for my ecu consist of and how would i check my voltage on my tps? what should it be at?

ryclef331 · Feb 26, 2007

Venom95 said:
thats it.....does it just fine tune the idling? I used the stop screw on the other side to adjust the base idle..

Hit the BRAKES!

Did you set the TPS Voltage and then use the stop screw to adjust the idle? If so, your TPS voltage is off again. You need to set TPS Voltage, unplug the IAC Valve, start the car. If it doesn't start, turn the screw (the one behind the rubber plug) IN about a turn or so. Do this until the car starts. Fine tune the idle from here. You car is cammed so it might take a bit of work to get it to stay running without the IAC. The idle screw also might not be sufficient enough to let enough air through. Some guys drill a 3/16th" hole in the throttle blade to help a bit more. You CAN set the idle using the stop screw and then go BACK and set your TPS voltage but I like to set the voltage FIRST and then set my idle using the screw. Using the stop screw to me is kinda bogus. Our cars have a throttle air screw for a reason....use'em! Your BEST bet is to do ALL of this after the car is at operating temp (open loop mode). Once the car is idling on its own, shut it down, plug the IAC BACK in. Your idle should be set!

Again though, with out a decent tune, you might get the occasional surge during cold start ups and coming to a stop at lights. I've got a chip and tune and I still get a lil bit of surging at lights from time to time.

purplehaze, tuning consists of strapping your car on a dyno and having the ECU chipped specifically FOR your car. As for checking TPS voltage, turn your key ON but engine OFF. Find your TPS sensor on the throttle body. Is the small of the two black things hanging off of it. Find the three wires in the harness, you may have to cut back some of the sleeve. Locate the middle grey wire with the white stripe. This is the signal wire to the ECU. Take a voltmeter and with the positive lead, probe this wire....just stab it through the insulation is what I do. Stick the ground lead to a good chassis ground. You SHOULD read between .97-.99 volts with the key on, engine off. If you DON'T, loose the screws and turn the sensor housing until you do. If you can't quite get it, take a drill and slightly elongate the holes of the sensor and try again. once you get it, tighten it down. Thats it.