99 Mustang GT won't stay running...

stangman16 · Nov 16, 2004

I have a 99 mustang GT that will not stay running. I have to keep my foot on the gas. Sometimes if I let off it'll idle between 300-500 rpms, fluctuating between the two. I had this problem about 2 weeks ago, and i put fuel injector cleaner in the gas tank (the additive) and ran the car for a little bit and it cleared it up. I tried that again, but am having no success. The car smells like exhaust pretty badly too. There was a noise at the front of the engine, sounded like a pump almost. It was a little loud at first, but as I kept the engine at 1000rpm, it started to go away, and after it went away mostly, the car would idle at the 300-500rpm range.

Could my problem be the smog pump? Is there any way I can test this? Could I take off the belt and start the engine to see if it'll run? Or would that cause some major damage? No check engine light is on either. This is very strange, the car has only 61K miles on it. Someone at work suggested it may be a fuel filter? I'm not sure if/where there is one on this car... and if my '66 stang ran, I would have a car for work. Any ideas?

codyGT · Nov 16, 2004

It is most likely the Idle Air Control Motor on the front of the plenum.

They do this when they go bad.

stangman16 · Nov 16, 2004

Is that a part I can pick up at a local parts store? Or is it a Ford item only...? I'll most definitely replace that to get this thing back on the road.

COramprat · Nov 16, 2004

They are about 40 buck at the dealer but most parts stores have them too. You can try cleaning it with some carb cleaner but that is a temp fix at best.

Dan_Soprano · Nov 16, 2004

Fuel Filter is located right infront of the gas tank. Its an easy change. You should have been changing it AT LEAST evry 30,000 miles. I change mine every other oil change. From the sound of it, it could be a number of things. 1. most common on fords is the Air Idle Control (IAC) valve. 2. EGR Valve, 3. Throttle position sensor, 4. Vacuum Leak. Try cleaning the IAC Valve and EGR valve with carb cleaner. un plug the plug on the Throttle Position sensor and see if the car will idle. DO NOT DRIVE IT with the TPS unpluged though. If the car idles normal with the TPS disconnected, then thats the problem. I had the same problem on my 01 GT. Took me a few days to figure out the TPS was the problem. My car wouldn't idle, changed the IAC, no joy. Cleaned the EGR, no Joy. I was about to take it to the dealer because I was getting pissed. I unpluged the TPS for the hell of it and BAM!! Nice smooth idle. Changed the TPS and never had a problem after. Like I said, this is just a suggestion. It very well may be your IAC, but it that doesn't work then you have other ideas. It's much easier to unplug the TPS and see what happens before you have to blow $40 on an IAC. Good luck!!

Dan_Soprano · Nov 16, 2004

P.S. the TPS in the black plastic sensor with the 2 wires on your Throttle Body. if you do disconnect it, your check engine light will come on. this is normal. it will go out when the sensor is plugged back in.

COramprat · Nov 16, 2004

Dan_Soprano said:
P.S. the TPS in the black plastic sensor with the 2 wires on your Throttle Body. if you do disconnect it, your check engine light will come on. this is normal. it will go out when the sensor is plugged back in.

I had problems with my TPS also but it would run and idle rough/funny. I was just going by his mentioning having to hold the gas for it to keep running that it sounded like the IAC. That and the TPS will throw a code whereas the IAC will not give you a MIL (or it didn't on mine).

Another thing since you mentioned vacuum leak Dan, is those tubes that run form the air intake will cause it to do the same thing. I had the one from the TB to the intake loose and it would not idle. I just happened to knock it off when I was changing my spark plugs one time.

Dan_Soprano · Nov 16, 2004

coramprat said:
I had problems with my TPS also but it would run and idle rough/funny. I was just going by his mentioning having to hold the gas for it to keep running that it sounded like the IAC. That and the TPS will throw a code whereas the IAC will not give you a MIL (or it didn't on mine).

It all depends on whats wrong with the TPS. If the windings inside the TPS are open(broken), then it will throw the code and trip the SES light. If the resistance is broken down or raised due to corrosion or such, then it will send the ECU false readings and not trip the SES light.

joshheat25 · Nov 16, 2004

I am also having problems with my stangs idle I was wondering where I could get a diagram of all these parts you are talking about just like this diagram.

COramprat · Nov 16, 2004

joshheat25 said:
I am also having problems with my stangs idle I was wondering where I could get a diagram of all these parts you are talking about just like this diagram.

If you look at the pic I attached above you can see the TPS in the upper left just behind the strut tower brace. The EGR is in the lower right. You can see about 1/4 of it. It is the disc shaped part.

COramprat · Nov 16, 2004

Dan_Soprano said:
It all depends on whats wrong with the TPS. If the windings inside the TPS are open(broken), then it will throw the code and trip the SES light. If the resistance is broken down or raised due to corrosion or such, then it will send the ECU false readings and not trip the SES light.

OK...gotcha. But did you have trouble keeping it running ie. having to give it gas so it wouldn't die or did you have a rough idle? This is the difference I found with the IAC (would not idle) and the TPS (rough idle).

Dan_Soprano · Nov 16, 2004

MODS, Can we make this thread a sticky?? It seems that this is a common problem. I know I have personally answered tech questions about this same thing at least on a monthly basis. Good tech thread.

~Dan

stangman16 · Nov 16, 2004

which one is the TPS? I'm going to try and disconnect it... i don't know which one for sure it is from that picture... anyway you can circle it?

And I guess if i disconnect that and it does not work, then just go get another IAC from the parts store? I need to get back up and running soon. I get out of work at 7pm tonight, so i'm anxious to give things a try. Thanks for the reponses.

kstang69 · Nov 16, 2004

ive been havin the same problem so it must be pretty common. For me the rpms sometimes dip way low when i am braking and the engine has died before. Rpms jump up and down while im stopped and sometimes i have to give it some gas to keep it running. Is it bad to be driving while i have this problem?

kstang69 · Nov 16, 2004

how much does the tps run?

Dark Knight GT · Nov 16, 2004

I have a 99 mustang GT that will not stay running. I have to keep my foot on the gas. Sometimes if I let off it'll idle between 300-500 rpms, fluctuating between the two. I had this problem about 2 weeks ago, and i put fuel injector cleaner in the gas tank (the additive) and ran the car for a little bit and it cleared it up

Brother had a similar problem and fuel treatment cleared it up, just like in your case.

I tried that again, but am having no success. The car smells like exhaust pretty badly too. There was a noise at the front of the engine, sounded like a pump almost. It was a little loud at first, but as I kept the engine at 1000rpm, it started to go away, and after it went away mostly, the car would idle at the 300-500rpm range.

It could be a vaccum leak, bad/dirty IAC, or bad front o2 sensors. I'm imagining you should have a SES light if any of these were the case.

Could my problem be the smog pump? Is there any way I can test this? Could I take off the belt and start the engine to see if it'll run? Or would that cause some major damage? No check engine light is on either. This is very strange, the car has only 61K miles on it. Someone at work suggested it may be a fuel filter? I'm not sure if/where there is one on this car... and if my '66 stang ran, I would have a car for work. Any ideas?

Don't bother with removing the belt, thats not a good idea. If the SES light isn't on, then we can only give you so much assistance. If you get the SES light, then by all means get the codes pulled so we can narrow down the problem. Dan Soprano probably has the best advice by saying to keep the fuel filter changed and to check the IAC. I would also say if its been a while, change the plugs and clean the fuel injectors. I'de also double check my intake for an intake leak and check my exhuast for an exhuast leak. Just my advice.

Dark Knight GT · Nov 16, 2004

kstang69 said:
how much does the tps run?

If you mean "run" as in "cost", then I'de say about 30 bucks. I remember about 3 years ago I broke my TPS sensor and it cost 30 dollars for a new one at the Local Ford dealership.

Might want to try giving Randy Stinchcomb at Liberty Ford out of Maryland a call and see what he can do for you. You can contact him online over in the Ford Parts section of the Modular Depot Forums board.

stangman16 · Nov 16, 2004

Yeah, no check engine light comes on (SES). And I'm not sure when the spark plugs have been changed, or the fuel filter. I'll try getting an AIC tonight, if the parts stores sell them. (any clue if they do?) I won't get a chance to call them for another 2 1/4 hours... I have a code scanner at home i can get... but I guess that is not going to do good since the SES light is not on...?

kstang69 · Nov 16, 2004

Thanks alot

Dark Knight GT · Nov 17, 2004

stangman16 said:
Yeah, no check engine light comes on (SES). And I'm not sure when the spark plugs have been changed, or the fuel filter. I'll try getting an AIC tonight, if the parts stores sell them. (any clue if they do?) I won't get a chance to call them for another 2 1/4 hours... I have a code scanner at home i can get... but I guess that is not going to do good since the SES light is not on...?

You can buy a New IAC from any auto parts store like Autozone, Advanced Auto, Napa, etc. You can also buy them from your local Ford dealership. Before you go buying a NEW IAC, might want to get some Carb & Choke cleaner and clean the one you got now along with spraying a bit in the upper intake. Might want to try using some of that "Seafoam" stuff in the Gas tank and/or crankcase as it works great to clear up carbon build up. Just a suggestion.

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