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99 STS
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93 Posts
Discussion Starter #1
I have 99 STS with 149,000 miles. No codes. My car runs great until I turn on AC. Then it starts misfiring really bad. I recently had AC charged by a trusted shop. Any
ideas what is causing my problem?
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
When's the last time the TB was cleaned?

How old are the plugs/wires?
 

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99 STS
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93 Posts
Discussion Starter #3
Throttle Body-I have never cleaned it. Not really sure what it is.
Plugs/Wires-Probably 40,000 miles.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,405 Posts
The throttlebody is the one-barrel fuel injection air intake equivalent of the old carburetor casting that contained the throttle butterflies, idle air passages and enrichment fuel bleeds.

In our cars it's the casting with a slew of cables and vacuum lines attached - the ducting from the air filter is clamped to the intake side.

To clean the thing, you use lint-free rags, a toothbrush and ........ spray throttlebody cleaner. Using a length of wood or even a golf club against the gas pedal, adjust the front driver's seat to fully open the throttle. Under the hood, remove asny rubber intake ducting at the throttlebody and push rags under the casting. You should be able to see fairly deeply into the TB bore. Judiciously (so as not to flood the intake manifold) spray, scrub, wipe the bore and throttle blade to squeaky clean. Reassemble. Make sure the intake ducting and band clamp areas are free of air leaks.
 

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99 STS
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93 Posts
Discussion Starter #7
My misfire is fixed! I cleaned TB thoroughly. I replaced plugs and wires with AC Delco plugs (41-950) and Wires (748N). I'm embarrassed to say what I did to cause the misfire in the first place but I will anyway. When I changed ICM a couple of months ago, I accidently trapped a spark plug wire underneath the ICM. I bolted ICM down and pinched the heck out of the wire. I didn't notice it until today when I changed the plugs and wires. It was smashed under ICM. Live and learn I guess!
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,781 Posts
Don't feel too bad. I'm sure you are not the first to do something like that. We all have embarrassing tales we could tell. :canttalk:
 
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