03 gt woes

adamv7010 · Mar 8, 2014

Recently got into mustangs...but not to automotive performance.

Recently bought an 03 gt with a leaking intake manifold...

I replaced that with a new frpp manifold.

Before the swap I had a condition where it would stumble at idle a little, then during wot pulls it would act as if it were starving for fuel.

I really figured the leak was soaking a plug or two causing a misfire. I blew the plug bores out with air when I had the Mani off and got some liquid out of a couple.

I put it all back together and everything went smoothly. I replaced the gasket on the IAC simply because the ford store didn't have a valve on the shelf.

Long story short, with the new intake and dry plugs, I've still got a stumble at idle, which according to my live wire, is around 680-710rpm.

Anyone wanna guide me to a starting point? Are these 2v coils known for breaking up?

I have several k$ worth of diagnostic tools, but I don't have an IDS, so I can view most anything, just can't flash.

Any advice is welcomed.

Thanks

Adam

sent while driving recklessly

Burninriverdiver · Mar 8, 2014

What did the plugs look like when u took them out? I spilled coolant everywhere when I replaced my thermostat, it misfired so I took out plugs and dried everything up. It continued to misfire until I replaced the plugs... Don't know why but new ones did the trick

Goldmember · Mar 22, 2014

It could possibly be a coil. Stock coils are junk. If the rubber boot is showing its age/cracking, that'll cause a miss; sometimes the miss isn't bad enough to trip a CEL; if that happens a few good WOT pulls should trip it. (Worked for me.) They fail pretty commonly especially with age/miles.

RichV · Mar 22, 2014

What brand and where to get the best deals on the COPs?

My 3V probably needs them, it likes to stumble once in a while and I suspect the coils need replaced. Should the plugs be done at the same time?

Sorry to hijack OP.

MustangChris · Mar 25, 2014

Hi Adam!

To step in before any "weird tech" pops up:

#1) The 99-04 coils are prone to failure. In fact, 4v-COP guys (99-04 Cobras/Mach 1s) regularly DOWNGRADE to the traditional coil packs for reliability purposes (usually seen above 1,000 RWHP, but common on set ups 800+). Your SCT should be able to tell you what cylinder is missing. If so, move the COP to a new cylinder and see if there's a change.

#2) you can not "service" an IAC. You can only replace it. people claim to clean them with brake-cleaner, and such... and that's just fine and dandy for them... but in reality they are ONLY replaceable units, NOT serviceable. (i know you said that you just replaced the gasket, but I just dont want another member thinking this is an open door to giving you advice to clean it. lol)

#3) the intake manifolds are not usually prone to cracking (unless they are being hit with meth or n2o) -- did the previous owner work on the car at all? TQing the manifold down inproperly may have torqued in a funny way leading to the crack (just shooting in the dark.) If you your working on a red-necked rigged car, we could be looking at something else all together...

If you have a buddy with a mustang thats running properly, my first suggestion is to swap their IAC onto your car. They are pricey little bastards, but getting a working one is the only way to properly diagnose it. I think this is your problem, but man, I'd hate to see ya throw $60.00 at an IAC for it not to be... lol.

a few other options: dirty MAF, leaking gasket in the intake (either at the IAT location, or a coupler not tightened, etc.)

If i really thoguht it was a bad coil, it'd probably give you more problems than just at idle, just my $0.02.

adamv7010 · Mar 25, 2014

MustangChris said:
Hi Adam!

To step in before any "weird tech" pops up:

#1) The 99-04 coils are prone to failure. In fact, 4v-COP guys (99-04 Cobras/Mach 1s) regularly DOWNGRADE to the traditional coil packs for reliability purposes (usually seen above 1,000 RWHP, but common on set ups 800+). Your SCT should be able to tell you what cylinder is missing. If so, move the COP to a new cylinder and see if there's a change.

#2) you can not "service" an IAC. You can only replace it. people claim to clean them with brake-cleaner, and such... and that's just fine and dandy for them... but in reality they are ONLY replaceable units, NOT serviceable. (i know you said that you just replaced the gasket, but I just dont want another member thinking this is an open door to giving you advice to clean it. lol)

#3) the intake manifolds are not usually prone to cracking (unless they are being hit with meth or n2o) -- did the previous owner work on the car at all? TQing the manifold down inproperly may have torqued in a funny way leading to the crack (just shooting in the dark.) If you your working on a red-necked rigged car, we could be looking at something else all together...

If you have a buddy with a mustang thats running properly, my first suggestion is to swap their IAC onto your car. They are pricey little bastards, but getting a working one is the only way to properly diagnose it. I think this is your problem, but man, I'd hate to see ya throw $60.00 at an IAC for it not to be... lol.

a few other options: dirty MAF, leaking gasket in the intake (either at the IAT location, or a coupler not tightened, etc.)

If i really thoguht it was a bad coil, it'd probably give you more problems than just at idle, just my $0.02.

Sorry I haven't bumped this. The intake was cracked under the temp sensor where it mates to the head. I replaced it with a new frpp.

I saw no misfires during a drive cycle via my OTC, my snap on verdict, nor an sct device.

I replaced the short eBay cai with a thru fender model from late model...that helped a lot.

Soaking the IAC may not be a fix, but it helped a good bit. Cleaning the maf made a good bit of difference as well.

Now it idles much closer to how it should. It also runs smoother through the power band as well. I'm sure an IAC and new set of coils won't hurt at all, and when it gets back from paint, I'm sure I'll do those things.

I did replace the rail mounted fpr simply because I had a new one on the shelf and that made the most difference.

sent while driving recklessly