Hello,

I'm hoping you can help me with a problem.

I have a 2000 Mustang GT. The mods I know of are BBK CAI, Flowmaster cat-back, and short-throw shifter.

When I am idling with the air conditioner on, the car tends to idle very low. The RPMs will drop below 500, then bounce up to around 800-900 to recover. Occasionally, it will die because the RPMs drop too low.

Today, I started the car and wouldn't run at idle, even with the A/C off. It would die almost immediately. After checking several sensor connections and not finding anything obviously wrong, I started the car and took off, having to keep it at a higher idle when I would stop. After a few minutes, though, it would maintain it's own idle, although it was a little lower than I think it should be. I was going to stop by the service center, but with the problem not present, I figured I'd come back home and do some research first.

My first thought is dirty fuel filter. I'm going to change that over the weekend. I've only had the car a few weeks, and so far, all I've done is change the oil.

So, any thoughts as to what may be wrong?

Your help would be appreciated. Thanks!

Jerad

 

I had this same problem...it's been a while and I wish I still had the reciept but it turned out to be an air/fuel sensor if i remeber correctly ( don't remeber exactly what it was called or where it was unfortunatly..I could even reset it sometimes by disconnecting the battery then roconnecting it..the problem would eventually come back though. They put the car on the diangnosis machine and found it that way. Mine was under warrenty so i didn't need to pay.
BTW my car is a 2000gt as well.
Good luck hope this helps (if this is your problem it probably wouldn't hurt to change the fuel filter anyway.)

 

Ok, thanks. I'll look into that.

 

CHeck that the MAF sensor is working correctly and make sure the CAI is securely installed and there are no rips or holes anywhere. If there are any leaks between the MAF sensor and the intake manifold, the engine will be sucking in air, screwing up the MAF readings and making it run lean. This will produce the exact symptoms you describe. Good luck.

 

I was thinking about that too. I picked up a Haynes manual yesterday. The one I had for my two V6's and my wife's car was '94-99. Not sure how much is different between the '99s and '00s, but I figured I better be on the safe side.

The BBK CAI is an all-metal kit, from the filter to the TB. I'll check the connections though.

 

Does it only idle incorrectly when the motor is cold (i.e. first start up of the day or after sitting for an extended period of time)? It sounds like the IAC module, which is notorious on 4.6L cars.

 

Glad to know it's a notorious issue.

As to when it happens... The dying with the A/C on first happened after I drove an hour and a half, let the car sit for about 30 minutes total off and on during the next hour, then driving 1/2 hour.

The start and die was after I let it sit for 8 hours. After it warmed up, it was fine.

And it did it yesterday, too, after sitting for about 6 hours. Again, after warming up, it was fine.

It has not done it in the morning for me.

I cleaned the IAC on Monday with carb cleaner. So far, so good, but I need more time to see if it's gone.

And I don't know if it is related or not, but when my A/C is on, the clutch continuously engages and disengages. It'll kick on for a few seconds, then off for a few seconds, then back on a few, then off a few... and so on.

Jerad

 

The starting up and dieing after its been sitting for 6+ hours defintely sounds like the IAC, especially if it clears up after the car is warmed up.

Let me think a bit on the a/c.

 

Same problem, and cleaning the IAC worked for me!

 

And I don't know if it is related or not, but when my A/C is on, the clutch continuously engages and disengages. It'll kick on for a few seconds, then off for a few seconds, then back on a few, then off a few... and so on.

Jerad[/quote]

My car does the same. I think the variable idle speed relates to power usage. When sitting at lights the car clicks and the revs rise slightly then clicks again and the revs drop. Is this a good description of what is happening? Much more noticable when the a/c is on and lights, etc. Will also change depending if you are in gear or not. This I think relates to the self controlled idle.
Usually revs slightly higher when electrical drain is high and when also slightly higher when the car is engaged in gear.

Hope I am right and I hope this helps.

"England for the World cup!"

 

That's exactly what it does. Doesn't seem right though..

Jerad

 

Weird.... have either of you had your battery or altenator output checked?

 

I haven't done that, but I was curious about that. The first time that it died after starting, I had sat in the car for about 45 minutes listening to the radio during my lunch hour, with the car not running.

I've got so much to do this weekend, but I'll try to make that one of them.

 

I believe this is quite normal. The change in revs is not noticable on rev counter only audiably detectable. Never had my car shut down or fail to start. Dont think this could be a problem, just normal engine management to help the battery/alternator scenario under power load.
Also when downshifting at higher than average revs the a/c or heater runs faster. Again nothing significantly higher just noticable with the sound change.
Do you notice this also?

 

It's noticeable on the tachometer. My idle RPM is 500-800 RPM. When it dies or wants to die, it will go below the 500 RPM, and if I don't bring it up right away, it dies. With the A/C on, it cycles between 600-900.

Also, it's never failed to start. It always starts, but the RPMs wouldn't be high enough to maintain proper idle.

 

You are right. It does register on the tachometer. I ran several situations and it varied from 600 to 800. Never dropped below 600 or even tried to die. Even starting engine with everything on it had no problem.
I hope that whatever the problem is you get it figured out.
Will do some research.

 

The good news is that I haven't had the car die since I cleaned the IAC. However, it's only been 2 days. We'll see.

I'll keep you posted with what I find.

Jerad

 

I had this problem as well. It started out the same as yours, then wouldn't turn on, so I drove it around the block, and now it is ok again. Whether it happens again is when I decide to try to fix it.

 

And I don't know if it is related or not, but when my A/C is on, the clutch continuously engages and disengages. It'll kick on for a few seconds, then off for a few seconds, then back on a few, then off a few... and so on.

Jerad[/quote]

Re-reading this thread. Its not the clutch, its one of the pumps engaging and disengaging. If you have the engine running go watch it on one of the left pulleys. Maybe this is out of alignment or damaged?

 

mine does the same thing, but i think its my compresser for the a/c that turns on and off. i think its low on whatever coolant it uses. so it turns on, and then turns off when it realizes it doesnt have enough to continue, and then it repeats.