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i've got a stock 98 GT and heres the problem: i drove home last night for about an hour on the highway without any problems. this afternoon i turned the key and after about 5 seconds i heard a loud pop sound from the rear end (sounded kinda like someone threw a rock at the trunk). i got out and looked at the rear and noticed that there was white/clear exhaust coming out of only the right tailpipe. i got back in and noticed the RPMs dropping below 1000 (as usual) but then rising back up to 1250, then dropping again and rising back up and finally dropping below 1000 as i pull out and drive off. this is the first time this has ever happened so i'm kinda freaked out. can anyone please explain this to me???
 

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98BlueMustangGT4.6:

Haven't suffered your symptoms but a frequent problem is the idle air control (IAC) valve. It tends to get crudded up and you can clean it with carb cleaner or just replace it ($60). The cleaning will help for a while but eventually, it will have to be replaced. Lots of history on this little item at the Ford service counter and in many threads posted on this forum.

The IAC is the likely culprit, imho.
 

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98BlueMustangGT4.6:

I don't have my Haynes manual (a wise $18 investment!!) at hand but here goes:

Disconnect the battery.

Locate the shiny can on the throttle body (near the top of the intake manifold near the "horsey" plate. Disconnect the electrical lead.

Remove the bolts and be careful not to damage the o-ring. (You might want to pick up a new one ahead of time).

Get well away from the car because carb cleaner or brake cleaner is baaaad for your paint.

Spray some carb cleaner into a rag (like an old tee shirt) and wipe the innards of the IAC with the solvent-dampened rag so that the solvent dissolves the crud. Do not soak the IAC or it may not work at all when electric power is restored to it!!

Let the solvent dry off, lube the o-ring with engine oil, and reinstall the IAC. Snug down the bolts (but don't snap them off!!).

Plug in the connector again and re-connect the battery.

Test drive.

Good luck.

chris
 
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