Cold start idol surge

[sounnder]

Don't know if this has been covered in the past, and any search mentioning surge is huge. I get a wicked idol surge at startup until the car runs for a few minutes. I have to give it a little gas to keep it running. After that it is great.

The car has a MAC CAI, Crain 2301 cam. The rest of the induction is stock.

Any ideas?

[aaronlstiles]

It's the cam, install a IAC adjuster plate on the IAC motor. Will take care of just about all of it.

[buddha]

I've had really good luck with a lot of different cams doing this:

The base idle is nothing more than the idle that the computer has learned at whatever angle your throttle body is set at when at idle. This technically shouldn't change by itself but it's always good to check it because you never know what the dealer or previous owner did to the car before you had it.
Once you change the setting of the base idle you will definately want to go onto step 4 in this series of articles because if you move the base setting of the idle plate you also change the tps voltage at idle.

What is needed?
- Flathead screwdriver
- You'll also need a wrench to remove your battery cable

How to do it
1. Disconnect the battery's negative terminal to reset/clear the computer's memory. Leave it disconnected for 30 minutes. WARNING: Whenever removing your battery cables ALWAYS disconnect the negative battery cable first and reconnect it last. Otherwise you could destroy your computer or cause a battery explosion.
2. Disconnect the plug going to your idle motor which is located on the front of your throttle body.
3. Reconnect your battery's negative terminal.
4. Start the engine, and set the idle to the rpm you want with the stop screw on the bottom of the throttle body.
5. Turn off the engine.
6. Reconnect the plug on the idle motor
7. Make sure all accesories (radio, blower motor, a/c, lights, etc) are off and start the engine.
8. Let engine run for two minutes.
9. Turn engine off and wait two minutes then restart engine and let idle for two minutes with all accesories on.


Solving Idle Problems Part 4 Setting the TPS voltage

If you haven't already read how to do it a million times in all of the Mustang magazines then this is your chance. Here's how to check and adjust your TPS voltage. You may be asking, "What is a TPS"? Simply put its the Throttle Position Sensor. The TPS is a sensor that tells the ECM (computer) how much gas
you are giving it, which in turn lets the computer decide how much fuel and spark to give you.

What is needed?
- Phillips head screwdriver
- Two small straight pins
- Digital multimeter

Picture 1

How to do it
The TPS (picture 2 "B") basically bolts to the throttle body with two screws. (picture 2 "A") The holes that the screws go through on the TPS are elongated so you can twist the TPS in either direction to adjust it. To adjust the TPS all you have to do is loosen (don't take them out) both screws and move the TPS until you see the right voltage.

Picture 2

To hook the multimeter up you will have to pierce the green wire with a pin so you can check how much voltage is going through it. The red or positive (+) wire on your multimeter will go to the pin in the green wire. Then you'll have to either pierce the black wire and put the negative wire from the multimeter to it, or just put the black multimeter wire to a good engine ground.
Now to check the voltage turn on your multimeter and make sure all of the wires are hooked up right. Then turn the ignition key to the on position, but don't start the car. You should be getting a reading on your multimeter. It should be .98-.99 volts. If its not, then its time to loosen the screws on the TPS and move it around until you get it right. When its at the right voltage tighten the screws and re-check it. If you aren't too happy about piercing your TPS wires with pins then you could do what some Mustangers do. I've seen a few guys/gals buy a fuse holder and attach the two wires from the fuse holder to the green and black wires on the TPS. Then they use the fuse holder holes to check their TPS voltage.....Whatever you do, make sure you never put a fuse in that fuse holder.
If for some reason you cannot get the voltage reading right you have two options. Either buy a new TPS or take off the old one and elongate the holes a little more with a file or a dremel.

I always do the TPS fist, and have to admit I've never unhooked the battery to clear the memory. Can't hurt I suppose. Here's where I copied this from:

http://www.stangnet.com/mustang-forums/ ... gh.507908/

[sounnder]

Thanks for the responses. I will be working on it when I get a couple days off.

[aaronlstiles]

I've done this a few times, and find I always need an IAC adjustment plate with bigger cams

[WillyB93]

My red car had a cam in it, I had an idle surge also. After a couple IAC adjustments I found out that the upper intake gasket was bad, replaced and fixed the problem.

[93Cobra#2771]

One other possibility - the CAI. Sometimes, CAI cause issues with the MAF reading the airflow correctly. Usually happens when there is a curve in front of the MAF.

Try removing the CAI and putting the stock airbox back on just to see what happens.

And finally, your IAC valve could be sticking when it's cold. Good idea to pull it and give it a good cleaning out to make sure it moves properly all the time.

[sounnder]

I plan on cleaning all of the induction parts when I get some car time. Unfortunately I dont have the stock airbox so putting that on is not an option.

Thanks!

[93Cobra#2771]

And finally, one other thing to check - look down the MAF and check that the sensing wires aren't contaminated. They should be clean and shiny. You can spray some electrical contact cleaner and GENTLY and CAREFULLY clean the wires with a qtip.

Welcome to the wide world of cold idle start up surge.

[sounnder]

So, I got the IAC adjuster plate installed, set it up per the instructions that came with it, and started it up. MAN, it was nice not to have to feather the throttle for 5 minutes to keep the car running during a cold start.

Drove the car around for a little while and noticed the idol hanging between 1100 and 1300 RPM's while idling at a stop.

I didn’t have time to work on the other probable trouble areas like cleaning everything in the induction system. I will do that the next car play day. One thing I did find was that the inside of the MAC CAI appeared to be contaminated with dust. Further examination showed the air cleaner element was pretty dry and was dirty. I will do a cleaning of the air cleaner element, MAF, and throttle body and see what the results are.

[mekessler]

When you do your cleaning on the air filter don't spray oil on it. Just soap and water and let it dry the engine will suck the oil thru the mass air meter and you'll be back at square one with a dirty oily meter that causes driving problems. I usually just blow air thru the inside out and reinstall it.

[93Cobra#2771]

If the filter is supposed to use oiled media I would highly recommend you reoil. The oil is what catches the dirt. Otherwise you need to replace with an element that is rated for use with no oil.

The trick is to not overoil the element.

[hnkstang50]

i agree the cold start idle surge is from the cam/mass air setup. i disagree with the iac aduster plate. if you think of it the plate is no different from turning the throttle body stop screw other than it will not change the tps reading (i think this was the sole purpose of the plate, simple idle adjustments). both will bypass air past the idle motor and adjust the idle. i wouldnt waste the money on one and if you need to turn up the idle just adjust the tps after turning the throttle stop.

the computer is trying to keep a certain idle so when you turn it up you are basicly leaving the idle motor to do no work. also the eec can then start to use timing to influence the idle too. it usually gives you a hanging idle.

ive fixed quite a fuel cold start idle surges such as your issue. its really hapening due to a rich cold start condition. the cam and aftermarket meters both can cause this. turning up the idle can help but if you got a tune or were able to lean out the idle then it would get rid of this surge. the surge goes away usualy once the o2 sensors are warment up and are working then the computer can make adjustments.

[k98dave]

"The trick is to not overoil the element"

That's what most people tend to do. I also found that the MAF elements tend to get a light coating of oil and then start to pick up dust.

I had a BBK CAI with a cheap oiled cone filter on my 88 when I first got it and had this problem. I got rid of all of that and went with a stock air box (you can still find them in salvage yards and e bay) with a K&N stock filter and the car ran much better.

CAI systems don't give any advantage as the intake air will be whatever ambient temp is. Once you are driving the air is moving through the intake too fast to pick up any additional engine heat.

[93Cobra#2771]

Agreed - the point I was making was if you have an air filter element that is designed for use with oil, you should use oil. Otherwise, there is a very good chance the media will not stop the dirt that is designed to stop using the oil.