razor9546

i have been plagued with this issue for too long and i'm starting to think it's time to give up on the car. this problem is half the time i'm driving when i'm slowing down with the clutch depressed the idle goes to about 400 and once i reach a complete stop and fixes itself. half the times the car drives fine for a day or two then this happens. sometimes after driving on the highway for a little when i try to come to a stop and idles too low and cuts off, then it refuses to start for a few tries, which leads me to think it could possibly be a fuel issue (bad pump bad filter?). i was under the impression it was something with the air. the air intake is new, the tb and upper intake is new, i replaced the tps, cleaned the iac, replaced the iac (made it worse so i put on the old one) reset the cpu and re learned the idle multiple times, cleaned maf with maf cleaner, tried fuel cleaners, used premium gas, took it to a mechanic and they replaced the oil temp sensor and coolant sensor and said that should more than fix it and they said i should invest in bigger injectors because im cramming too much air? bs its only a 70mm tb and a k&n intake. i had this idle issue before i even added the cai and tb so. the last thing i can think it could be is maybe the pump is starting to go bad, but wouldn't that mean the car would cut off at any time rather then just slowing down? when the car idles bad, ill sometimes at a light shut it off and start it up and hope it clears itself up and sometimes it hesitates to start, almost like it won't fully fire. sorry for rambling on here guys but i'm just really frustrated, i've put a lot of money into this car since i bought it and put a lot of money into this issue and nothing seems to fix it, not even the damn mechanic. please feel free to post solutions or ideas. thanks for reading.

also, one more thing to note, today when i was driving home from class, it cut off after i got off the high way slowing down to traffic, once i got it to start back up after 3 tries the fuel gauge jumped from 3/4 to full, could that mean anything? it went back down to 3/4 after 5 minutes of driving, then the full mark on the gauge started to flash blue for a few minutes? but if that means anything hey, just trying to explain as much as i can so someone can try to assist me.


here's what happens when it acts up. i was sitting in my drive way giving it small revs to show how it drops constantly. eventually after driving for a while it'll stop but comes back eventually.

CalBoy101

Razor, a sticky EGR valve can give the symptoms you are having, what happens is that it opens during cruise, when you let off the gas it is supposed to close but if its sticky that happens too slowly and the car stalls.

On my prior car (chevy) this was easy to check, if you disconnected the electrical connector to the EGR solenoid valve it kept the EGR from opening and on my car that caused the stalling problem to go away so I knew it was a bad valve and replaced it.

I don't know if there is any easy way to temporarily disable the EGR on our Mustangs to do this test, maybe someone can chime in on this?

The flakey gas gauge could possibly be related to your problem, you might have a bad ground in the car somewhere.

Under the hood I know there is one ground up front on the passenger side and probably some more closer to the fuse box. If these look corroded at all, take them apart, clean all the metal to metal surfaces down to bare metal, including the contact point on the car, put either dielectric grease or vasoline on them and put it back together. There is probably also a ground somewhere on the gas tank you should also clean.

Its also possible that the sender element in the gas gauge is getting worn out, causing it to give flakey readings.

razor9546

thanks for the response. i'm going to go ahead and replace the egr and see where that takes me, did some research and a lot of my symptoms do actually fall under a bad egr.

71_340

I had that problem on a Crown Vic 4.6 I used to own. Cleaning the idle motor plunger solved it, it was gummed up and sticking; use throttle body cleaner. It's worth a shot and a whole lot cheaper than an EGR valve.

71_340

Did you ever solve your idle problem? If so, post your solution for everybody's benefit.

GTLee

I had the voltage regulator on an alternator go out on my 04 and my car idled the same way, still charged fine battery fine but made my car run bad and throw codes. Just a thought.

Friel

Is that the same thing as the iac?

razor9546

pretty sure i corrected the problem and there was nothing mechanically wrong with the car the whole time. all i did was reset the car cpu, and let it idle but idle without the iac plugged in. i had to adjust the stop screw a lot from where it was set and let me tell you that made all the difference. i can feel the response back and the low end power is back. here's the steps i followed and how to fix it if anyone is curious.

Disconnect the negative terminal to your battery and turn on your headlights for about 10 minutes(there's a lot of speculation as to how long. some people will even say to disconnect the positive terminal and some people will say to leave it disconnected over night.)

Disconnect the wiring harness connector to the IAC

Turn off headlights and reconnect battery. DO NOT TOUCH THE GAS PEDAL!!

DO NOT TOUCH THE GAS PEDAL!! Try to start the car. If the car won't start adjust the set screw on the throttle body a 1/4 - 1/2 turn and try again. Repeat until the car will stay running. It will run rough but that is what you want.

Let the car sit and idle (DO NOT TOUCH THE GAS PEDAL!!!) until the car reaches operating temperature.

DO NOT TOUCH THE GAS PEDAL!!! Step 5 allows the computer to relearn idle settings. It's pretty cool when you follow my procedure because you can actually hear and feel the car figuring out the proper idle settings. It will go from idling rough to idling smooth as it warms up. Once the car is warmed up verify that the car is idling at around 700rpm. If the car is not idling where you want it, adjust the screw until it hits ~700rpm and then let is sit maybe another 10 minutes DO NOT TOUCH THE GAS PEDAL!!! DO NOT TOUCH THE GAS PEDAL!!!

Turn the car off. Reattach IAC wiring harness. Start the car and let it idle for about 10 minutes. Take it for a drive and see the difference!

71_340

Yes! IAC = Intake Air Control valve, there are several names for it (depending on the manufacturer).

They all do the same thing, keeping the idle speed at a preset RPM no matter what the load on the engine is (i.e. A/C on).

71_340

Just don't forget to adjust the throttle stop to the original setting when you done! It isn't meant to be a permanent idle adjustment.