View Full Version : K&N on and now it wont idle

05-18-2004, 08:08 PM
I have a 99 Cobra that I finally got around to putting a K&N filter on and I decided to take off the air silencer off as well. Im pretty sure this filter has been on since it was born and its pretty damn nasty. When I did these two things to the car I cranked it up and it would only run if I was giving it gas, once i let off down she went no idle AT ALL. I disconnected the battery now to see if itll reset the computer to compensate and I havent tried it yet, I mean its a bigger difference than you guys are probably thinking (yeah the old filter was really dirty) Hopefully itll work and the computer will adjust when i get out there, but if you guys have any suggestions as to what I should do let me know. Im a little concerned so Id appreciate any help I can get from you boys.


ps I also was gonna put on a brand new belt as its time for that but i got to looking and it looks like a hell of a chore, you guys got any tips for that too?

05-18-2004, 09:04 PM

You did the right thing by disconnecting the battery and letting the computer reset. That should solve the problem but if it doesn't then make sure there are no air leaks or you may have an idling problem.

Replacing the belt is a one person job. Simply use a socket wrench to move the idler down and the belt will slip right off. Do the opposite to put the new one back on. Never try to put the belt back on a small pulley. It's always easier if you leave the large pulley for last.

HTH :thumbsup:

05-18-2004, 09:12 PM
Well that little reset deal didint work, at all, I even took it out for a drive if you want to call it that and it was terrible even when i depressed the clutch the revs were dropping very quickly. The thing is, I didnt disconnect the battery until after i tried to start it up the first time that I had the silencer off and the K&N on. Any more suggestions guys, Ive even put the old filter back on and its doing the same thing. Is it somehow possible that when I disconnected the MAF with the battery still hooked up that I have managed to throw the MAF off or something.

Thanks again

05-18-2004, 09:54 PM
Ok boys check this one out. So i just got back from putting the air silencer on along with that same dirty filter. Low and behold the damn thing works like a charm once again, there is something to that damn air silencer, I never have liked the idea of it but apparently for me its a F**KING neccessity. Well at this point I think Im gonna go try to f**k it up a little bit more if i can and see if the K&N will work in there with the air silencer. If anyone else has had this kinda thing happen to them let me know and we will let Guiness Book hear about it.

05-18-2004, 10:52 PM
I'm assuming it is an open filter and not one that goes in the box, is that right? W :doubt: hat else did you change?

05-18-2004, 11:27 PM
You didn't change the filter while the car was running did you? I have heard that if you do that then you have to reprogram the computer or do something to the computer. Maybe this is just a rumor. :doubt:

05-19-2004, 12:51 AM
I have the same year car as you have, and removing your air silencer shouldn't stop your car from running.. I took my off months ago.. It runs and sounds better.. you may want to double check what you did and try it again..

05-19-2004, 06:56 AM
Here is my 2 cents worth. For starters, the battery should be disconnected for at least 1/2 hour if not longer, this will allow the computer to clear all memory and begin a full reset in the data logging for adjusting for the new air flow. In fact the computer will adjust fuel/air mixture, and timing for the change. Now for the tricky part. Since you had a dirty air filter, when changing to a free flowing type, there are several things that may occur. Most guaze or foam type filters are usually coated with too much oil which may find its way onto the MAF. Even if the MAF does not look dirty, it may be compromized by film on it. First, go out and buy a small can of electrical motor cleaner to clean off the sensor elements of the MAF. To clean the MAF either purchase a security bit to remove the two screws to remove the MAF and spray it with the electrical cleaner or you can take appart the assembly and spray it into the hole where the MAF is. You could clean it with alcohol and a Q-tip but be careful not to bend the probes. A dirty MAF is one of the little things that can rob you of some HP. Secondly, it sounds like the IAC valve may need cleaning or replacement. Since you have a 99, the by-pass passages are in the intake plenum. Since this is one of the components used to maintain idle, it may be dirty. To test it, simply un-plug it and start the car, it should idle close to 1200 to 2000 rpm. Plug it in and if the idle drops below 800 rpm the IAC may be gummed up or faulty. To locate the IAC, it is mounted on the intake plenum next to the throttle body at the back side of the plenum. It has is a round cylinder about 2.5 inches long with a diamond shaped mounting plate. A new one will cost about $80.00. However, if it is removed from the intake, you can inspect the pintle (shaft) if it is dirty the movement will be restricted. you can clean this out with the electrical cleaner too along with a q-tip. Keep the cylinder upwards to prevent any of the cleaning fluids from getting into the solenoid body. Once clean remount. Another thing to consider is the throttle plate, inspect it if it is diryt. You should clean off the plate with a good intake cleaner for use with fuel injected engines. With everything all cleaned up. re-connect the battery (it is best to start the cleaning process with the battery disconnected so the memory is cleared by the time you are done cleaning all the parts). Last but not least, check all the clamps (throttle body, MAF) and the seal at the filter of the housing. Inspect all plug connections (MAF, IAC, Temp probe- the other wire plug close to the MAF, and throttle body position sensor). A note: if the throttle plates have any holes in it, I would suspect there was a problem previously with the idle. the IAC does a good job in maintaining idle which feed air through two small passages located above the throttle plates which is about 3/8" in diameter. If you have a sticky EGR valve, and it the throttle plates are gummed up, the condition of the IAC valve will be the same. Don't be surprised if the check engine light comes on, which will indicate the IAC is causing out of range idle speed. It will trip once you unplug it while the engine is running. that can be reset by disconnecting the battery, or if all seems good, then it pops on, have the codes checked at Autozone or similar location that will read the codes at no cost.
I will post the 1999 codes for reference after this post. In fact, I have had very much the same issues after installing a CAI (cold air induction) kit. Once you get the idea of how all this electronic stuff works, it is not as hard as it appears. GOOD LUCK in getting your Cobra to breath better, it just has a bit of a cold for the time being. :cool:

05-19-2004, 06:59 AM
Here is a link to all of the ODBII codes for the 1999 Cobra, which is also good for up to 2004 since the platform is still the same (unless they came out with ODBIII) notice there is codes for superchargers in there too.


05-19-2004, 10:46 PM
Hey guys thanks a lot for all of the help but later that night me and my friend went back to it and once we had her running ok with the K&N and the silencer in place we went back and took the silencer off again and she is purring like a kitten, good as new, very normal idle, and even a cleaner throatier exhaust note. I think that my computer had some issues adjusting to both at the same time and once it had a second to adjust to the addition of only the K&N and it found its idle again it got it closer to being able to adjust to the also new setup of the new filter and the silencer gone. I may be crazy but I had my friend who is pretty knowledgeable with mustangs helping out the whole way and I will say we are both just completely stumped. Im even thinking of writing into that section of Muscle Mustangs and Fast Fords, ya know Yo Bernie ask Ken. I think they may just tell me I did it differently than im saying that I did or that a seal was wrong the first time. I triple checked everything the first through the last time and I had my $hit right. Im so confused but at the same time just happy it all worked out right. Hmm chime in if this makes you feel like your IQ is somewhere south of 65, I know it did with me.


05-19-2004, 11:51 PM
Glad to hear everything worked out great.. :thumbsup: