First off, the car is completely stock. I had been having problems with the engine running rough, acting like its missing or not firing. Took it to the dealership, they said I needed a fuel pump and an "induction service" for like 1100 bucks. It didn't sound right to me, so I took it to a local guy and he finds the spark plug wires are very worn and shorting out, so he replaces the plugs and wires. Car runs great now, except now the Service Engine Soon light is on, and he said I just need to reset the computer to turn off the light, but I think it is actually indicating something. I haven't checked the code yet. I think I have an apparent idle problem. When starting the car cold, the idle goes high (about 1100), then settles around 900, like normal. But when I put it in drive, the idle starts to fluctuate repeatedly from 300 to 700, but the car does not die. Pushing on the gas doesn't really help. After it warms up for a minute, the problem goes away. I also noticed that when coming to a stop, when the auto transmission is downshifting, it downshifts hard, like the engine is revved high while shifting, making is surge forward a little. Any thoughts are greatly appreciated!
An unstable or high idle seems to be a common problem with the 3.8L, and no one seems to know for sure why. You might check to see if you have a vacuum leak somewhere. As for the CEL, you can check for a code, but it's probably a misfire code left over from the bad plugs and wires. Use a scanner to reset it and then see if it returns. If all you have is a strange idle and everything else is normal, you might want to just live with it.
Anyone else have any thoughts on this? I'm going to start troubleshooting this weekend. Thanks again, all!
Hey,not sure if you are still having this problem.First off ,what year is your stang? Sorry I'm posting via mobile and can't see your specs.I am asking because I'm unsure or not whether your trans has a TV cable.Or perhaps a TV sensor with vacuum hose.If there's a vacuum leak in that area,not only will your engine's idle surge,your trans will either shift too early or too late and very harsh. Maybe someone else here can clarify this.
It's the idle air control or IAC. I had the same problem on a 94 with the 3.8. I tested it according to my chilton/haynes manual and even though it checked good, I decided to replace it. Bought one from the local AZ and that fixed the problem. It fixed the high idle at startup when cold, and also fixed the higher than normal idle problem when driving. Used to could just idle and cruise at about 25 MPH. Works like a champ now. Might be your problem too.
Thanks for the feedback, guys! Ogre, I've been suspecting its the IAC, but haven't replaced it yet. I might just do that and see what happens. I can probably return it if that isnt the problem. MustangLX-5.0, My car is a 2002, totally stock. Thanks again!
ant_knee,if you do get a new IAC,make sure you don't buy it from Autozone.Any other place is fine.Autozone has a history of poor quality parts.You may end up with a far more worse idle problem using their parts.
I've heard that about AZ electical sensors/parts too. I got mine from there anyway, and luckily it's worked fine.
Does the V6 have the same IAC as the V8? Was just looking online and some sites only have them for 4.6L V8.
I don't believe they are the same.The 4.6 has a different throttle body setup. Check the part numbers for both models.If they match..use the other.i doubt it will though.
If you want..im at work right now.I can run to parts dept. and ask them to look up the iac's ed.. Just checked with parts.They are totally different IAC'S.right down to the part numbers.
If you disconnect the negative battery cable for 20 miuntes, it will reset your DTC's and the check engine light will go away.
