My v6 Mustang has a problem nobody can find or fix
10-15-2016, 08:22 AM
#1
Thread Starter
Join Date: Oct 2016
Location: PA
Posts: 1
My v6 Mustang has a problem nobody can find or fix
Hello Everyone I just wanted to make this post because I am now out of ideas. Nobody can help me anymore with my 1999 v6 mustang. The problem is it has this low idle. It will be sitting at 800 rpm and then it will go down to 600 and realize its to low and jump up to 800 again. I does this every like 5 seconds and only when it warms up! At cold it will stay at around 900 for the most part. But the thing is when it does this you can see the engine sake side to side for 1 second before it jumps back up to 800 rpms. The odd part is when driving if you try to accelerate quick it will kind of hiccup or misfire like it loses gas for like half a second 
I have been to 3 shops including the dealership and no success. The new mechanic says he is almost certain it is the ecu. But idk anymore!!!! Here is what I have replaced.
Fuel pump
Fuel filter
Ran some injector cleaner
New crank sensor
New spark plugs, Wires, and Ignition Coil pack
Could not locate any vacuum leaks
Cleaned mass air flow sensor
Car throws no codes
It just makes no ****ing sense. Also all this started AROUND the time my buddy hooked the battery up backwards when he jumped it. But my dilemma is the car still runs and while ****ty will accelerate and idle without stalling it is just so bad!!!! If you listen to the exhaust you can here it puttering and sputtering
My question is what the **** is this problem!!! does a ECU even make any sense. I don't know what to do or what to believe anymore. I have put 4 thousand into this car and I paid 3500 for it! Can anyone help me or have any good info please. Thank you guys
I have been to 3 shops including the dealership and no success. The new mechanic says he is almost certain it is the ecu. But idk anymore!!!! Here is what I have replaced.Fuel pump
Fuel filter
Ran some injector cleaner
New crank sensor
New spark plugs, Wires, and Ignition Coil pack
Could not locate any vacuum leaks
Cleaned mass air flow sensor
Car throws no codes
It just makes no ****ing sense. Also all this started AROUND the time my buddy hooked the battery up backwards when he jumped it. But my dilemma is the car still runs and while ****ty will accelerate and idle without stalling it is just so bad!!!! If you listen to the exhaust you can here it puttering and sputtering
My question is what the **** is this problem!!! does a ECU even make any sense. I don't know what to do or what to believe anymore. I have put 4 thousand into this car and I paid 3500 for it! Can anyone help me or have any good info please. Thank you guys
04-19-2018, 10:28 AM
#6
Join Date: Apr 2018
Location: FL
Posts: 6
Hello Everyone I just wanted to make this post because I am now out of ideas. Nobody can help me anymore with my 1999 v6 mustang. The problem is it has this low idle. It will be sitting at 800 rpm and then it will go down to 600 and realize its to low and jump up to 800 again. I does this every like 5 seconds and only when it warms up! At cold it will stay at around 900 for the most part. But the thing is when it does this you can see the engine sake side to side for 1 second before it jumps back up to 800 rpms. The odd part is when driving if you try to accelerate quick it will kind of hiccup or misfire like it loses gas for like half a second I have been to 3 shops including the dealership and no success. The new mechanic says he is almost certain it is the ecu. But idk anymore!!!! Here is what I have replaced.
Fuel pump
Fuel filter
Ran some injector cleaner
New crank sensor
New spark plugs, Wires, and Ignition Coil pack
Could not locate any vacuum leaks
Cleaned mass air flow sensor
Car throws no codes
It just makes no ****ing sense. Also all this started AROUND the time my buddy hooked the battery up backwards when he jumped it. But my dilemma is the car still runs and while ****ty will accelerate and idle without stalling it is just so bad!!!! If you listen to the exhaust you can here it puttering and sputtering
My question is what the **** is this problem!!! does a ECU even make any sense. I don't know what to do or what to believe anymore. I have put 4 thousand into this car and I paid 3500 for it! Can anyone help me or have any good info please. Thank you guys
I have been to 3 shops including the dealership and no success. The new mechanic says he is almost certain it is the ecu. But idk anymore!!!! Here is what I have replaced.Fuel pump
Fuel filter
Ran some injector cleaner
New crank sensor
New spark plugs, Wires, and Ignition Coil pack
Could not locate any vacuum leaks
Cleaned mass air flow sensor
Car throws no codes
It just makes no ****ing sense. Also all this started AROUND the time my buddy hooked the battery up backwards when he jumped it. But my dilemma is the car still runs and while ****ty will accelerate and idle without stalling it is just so bad!!!! If you listen to the exhaust you can here it puttering and sputtering
My question is what the **** is this problem!!! does a ECU even make any sense. I don't know what to do or what to believe anymore. I have put 4 thousand into this car and I paid 3500 for it! Can anyone help me or have any good info please. Thank you guys
Also when I accelerate when going up a ramp in the highway and such, you know how you give it 50-60% throttle right? I do and it just hangs around 2000 rpm while not accelerating at all and having that same popping noise that you have from the exhaust or engine. I’m going to clean the MAF one of these days and if it helps I’ll post back here and tell you if it resolves my problem.
04-19-2018, 10:31 AM
#7
Join Date: Apr 2018
Location: FL
Posts: 6
I understand your pain. I’m having the same issues but I haven’t spent nearly as much money as you have on my car. Mostly due to me being practically poor. But I’ve narrowed it down to being the MAF sensor either bad or dirty. Pretty cheap solution to it, it’s about $8 in any autozone you go to, and a new air filter is $18 depending on what air filter you get. This has been a pain on my side for too long and I can’t wait to fix it. Mine starts with a high idle at around 1500 rpm and when the car gets warmer it gets to around 600!!
Also when I accelerate when going up a ramp in the highway and such, you know how you give it 50-60% throttle right? I do and it just hangs around 2000 rpm while not accelerating at all and having that same popping noise that you have from the exhaust or engine. I’m going to clean the MAF one of these days and if it helps I’ll post back here and tell you if it resolves my problem.
06-26-2018, 01:00 AM
#8
Join Date: Jun 2018
Location: Texas
Posts: 2
Me Too Me Too Me Tooooooo!
Brandon,
I feel your pain bro. I am going through the exact same thing with my same car. Keep in mind, every time that you make these changes to your engine on the intake, exhaust and/or emissions systems, especially any electrical component, if you can unplug, plug it, or see wires you should be disconnecting the negative side of the battery first and foremost!!!....<<<VERY IMPORTANT!!! If it is a short little 20 minute job like the TPS should have been, leave the battery disconnected for at least an hour. Reconnecting the negative side of the battery is the very last step of the job. You don't want to do this until you're certain you are ready to start the engine and verify your repairs were warranted. This resets the PCM, (what you are calling and ECU), trust me I know who cares or what's the difference right. Well for Ford the PCM does a little more than what an ECU does...so back to resetting the PCM. even after you make your repairs etc....the car has memory, similar to that which is in your smartphone, because of this fact the car has to relearn how to behave when receiving the correct signals into the PCM from the various sensors you have replaced etc...The car only needs 1 complete cycle I believe in order to achieve this. A cycle consists of various stages of engine temperature, speed and other variables. Needless to say you have to drive it a couple of times for some of the issues to smooth themselves out after replacing the parts. Once you begin replacing several parts like this....9 times of 10 they are going to snowball on you like that. Older cars, that's the nature of the beast. I recommend purchasing the CD of your car's shop manual. I always do, so that I can read up on how Ford states in needs to be done. Then I develop my way to do it. If you haven't replaced the TPS yet, unplug it while it is running....if nothing happens it's no good....they only cost like $20 and it's two screws. If you have then move on to replacing the IACValve.....another easy job, a little more costly though. Good Luck to you man. Hit me back if you want any more info...
P.S. I get a ton of my stuff from RockAuto.com including the CD of the ShopManual!
I feel your pain bro. I am going through the exact same thing with my same car. Keep in mind, every time that you make these changes to your engine on the intake, exhaust and/or emissions systems, especially any electrical component, if you can unplug, plug it, or see wires you should be disconnecting the negative side of the battery first and foremost!!!....<<<VERY IMPORTANT!!! If it is a short little 20 minute job like the TPS should have been, leave the battery disconnected for at least an hour. Reconnecting the negative side of the battery is the very last step of the job. You don't want to do this until you're certain you are ready to start the engine and verify your repairs were warranted. This resets the PCM, (what you are calling and ECU), trust me I know who cares or what's the difference right. Well for Ford the PCM does a little more than what an ECU does...so back to resetting the PCM. even after you make your repairs etc....the car has memory, similar to that which is in your smartphone, because of this fact the car has to relearn how to behave when receiving the correct signals into the PCM from the various sensors you have replaced etc...The car only needs 1 complete cycle I believe in order to achieve this. A cycle consists of various stages of engine temperature, speed and other variables. Needless to say you have to drive it a couple of times for some of the issues to smooth themselves out after replacing the parts. Once you begin replacing several parts like this....9 times of 10 they are going to snowball on you like that. Older cars, that's the nature of the beast. I recommend purchasing the CD of your car's shop manual. I always do, so that I can read up on how Ford states in needs to be done. Then I develop my way to do it. If you haven't replaced the TPS yet, unplug it while it is running....if nothing happens it's no good....they only cost like $20 and it's two screws. If you have then move on to replacing the IACValve.....another easy job, a little more costly though. Good Luck to you man. Hit me back if you want any more info...
P.S. I get a ton of my stuff from RockAuto.com including the CD of the ShopManual!
09-04-2018, 07:21 PM
#9
Join Date: Sep 2018
Location: Missouri
Posts: 13
Hooking up cables wrong trying to jump might of killed or hurt diodes in the alternator! And yes it's possible to test them with a cheap multi meter!! There's a u-tube video on how to check a ford alternator diodes... I checked mine earlier in the year didn't even take it off the car!!! It's a easy 10 minute test something to check.. Good luck and No Don't let someone replace the ecu 99 has anti theft system? Better have the keys that match the ecu if you don't have live data scanner? I suggest to Everyone without one to check in to the BAFAX Bluetooth Best tool I've bought in 30yr of working on Mustangs I've had 6 of them!
09-05-2018, 01:33 PM
#10
Gentleman's Relish
Join Date: Feb 2005
Location: AZ
Posts: 13,090
How does the throttle body blade look? Warm idle is very sensitive to buildup of any type of crude around the blade that changes the airflow. Bouncing could be caused from the car trying to correct for the throttle plate but because of dirt/interference from dirt, it's not able to find a sweet spot.
When cold, the throttle plate is open little than when warm so it's less affected by minor buildup.
When cold, the throttle plate is open little than when warm so it's less affected by minor buildup.
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