MustangWill

I'm not gonna lie, I don't know much about the workings of a car's engine. That's why I'm here. Basically, I changed my battery earlier today and hae started my car five times since then. The first two times were a normal ignition but the following three times, the RPM would jump to about 800-1000 like normal but then immediately dip down to about 300-500 RPM and then quicken back up. I thought that was weird. On top of that, the two most recent times I parked my car, the moment I shifted to park (auto transmission), the engine died. I didn't have to turn the key or anything.

A friend of mine told me this was a transmission problem, but I thought that was kind of strange since my transmission didn't have any signs of wear other than the occasional slightly-rocky downshift, and I thought that was expected for a car that had 76K miles.

But yeah, the car's a 99 Mustang GT Automatic.

Thanks for the help, guys, I really hope I don't have to do anything too dramatic with the car.

Colorado_Mustang

Sounds like it has an air control problem. If you look in the 4.6L section you'll find references to cleaning the IAC, which very well could be your problem. Also make sure the intake pipe is in good shape and has no cracks/holes/leaks.

KELRMN2

If all you did was replace your battery... take the car out and put some mile on it. May just to relearn.

MustangWill

Well, I'll check the air filter. I might need to recharge it. But yeah, I'm still thinking it's either the battery or transmission. I tried tightening the terminals and applying some terminal grease and I also checked the transmission fluid which was at normal levels and pretty normal coloring (orange reddish kinda like diluted blood.) but I'm still getting weird RPM fluctuations. I've had it drop to about 200-300 immediately after ignition, I've had it want to dip down to 100 or less right after I shift into park if it doesn't just go ahead and shut the engine down on it's own, and I've also had the RPM drop from about 1000 to 300 max during a sharp u-turn I made. So far I've only put about 30-40 miles on it since the battery so I guess I'll take it out for a drive again tomorrow while paying attention to the RPM. I'm also pretty sure the intake pipe is in good condition but I'll check it out. Something tells me I ought to have had the car fully inspected before I bought it...

MustangWill

:Bump

not stok 04

give it time for your computer to relearn if thats not the problem then check your mass air connection and it doesnt sound like a trans problem

hot wheels

there's over 20 pages with that same problem. idle hang, stalling, and/or eratic idling. i've got the same problem but mine started with my accufab tb/plm. going to work on it with my mechanic tomorrow. already changed the iac and i have a new maf because of my vortech. i've readthat fords are famous for their O2 sensors going bad which can cause the problems. if i find anything out i'll post it and it has nothing to do with your transmission.

hot wheels

just got back from the mechanics and this is what i found out, hopefully this helps someone - if your freon is a little low the a/c pump will continually engage and disengage, changing the rpms. my problem, ever so often when i would put my clutch in at a stop sign, the rpm's would drop normally at the same time the a/c pump would engage and then the stalling problem drawing too many rpm's. we disconnected the a/c, till i can get it charged. now it idles like it's new again. hope this idea helps someone it did me.

MustangWill

Well, right now, the car seems to only have the idle range play around during ignition and shifting. It still stalls out quite often right after I shift into park, though. How many miles would it take for the computer to relearn? Also, one thing I've noticed about the car when it stalls out is that usually it'll die down to about 100 and try to rev itself up again. If it then catches itself about to stall, the battery light indicator will show up. Then after it dies, the "service engine soon" light will show up.

How would I check that? I mean, I know where it is on the intake pipe, but what would I be looking for?

How would I check the freon levels? I'm not sure that adding the correct amount of freon will fix my problem, but I still think I ought to know how to check the levels just to make sure my air conditioning is in good working order.


Sorry, if my dilemma seems kinda bland. I wasn't quite sure what to type into the search box. And thanks for the help. Seriously. I don't personally know anyone with hands-on experience in maintaining a car so you don't know how much help you guys are.

Wilson

johnnyhou

Dude, first post was right, clean your IAC valve.