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Discussion Starter · #1 ·
88 5.0\S.D,AOD, stock, 2chamber flowmasters,h-pipe\no cats.

When I let the car idle in park it seems real ruff. RPM will rise to 900\1000
then fall to 400 then catch itself and level out. Then repeat. Also, does this in drive. But, it has yet to die. Drives normal when given gas and high speeds. Just not at idle.

- Have changed the spark plugs. That is it.

- Mustangs are new to me and any help or suggestions would be greatly appreciated.

-Blinker fluid levels are fine.
 

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A codes scan of the ECM would help. You could do the following as preventive maintenance and check if it takes care of the problem:
- check timing and calibrate it to 12-14° BTDC
- clean throttle body w/carb cleaner & nylon brush
- Reset ECM (disconnect battery neg. for 30 sec.) and,

check if it takes care of the problem otherwise, a scan is recommended.

 

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Discussion Starter · #3 ·
Thanks for the reply. Two questions.

1.What about the IAC?

2.Is there any way to check to see if it is working properly?
 

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Try disconnecting the battery cables, and cleaning them, and the battery terminals.
If you needed the plugs, you probably could use new wires. Find a completely dark spot, and look at the wires as the engine idles, see if there are arcs. Mine were arcing to the AC lines, among other things. If the wires are bad, get a cap and rotor too.
 

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seems like you are describing an IAC issue.remove it and clean it out,be sure the plunger moves freely.
 

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pillowtalk said:
Thanks for the reply. Two questions.

1.What about the IAC?

2.Is there any way to check to see if it is working properly?
I usually check them as part of the cleaning process. I disconnect the MAF/ intake hose/pipe and start the engine, disregarding any codes generated by doing so, let it idle and spray a little mist of carb cleaner in the TB, increasing the mist but, allowing the IAC to correct for the stumble. I keep increasing the mist and you can actually hear the IAC openning up. Let go of the carb cleaner mist and the idle should be over 1,200 RPM momentarily, you should hear it closing and the RPM's lowering to the system's normal RPM range in idle. You have to be very careful when doing this, you know, carb cleaner is flammable and you have spark plug wires @work nearby.
It it behaves as described, why replace a good part?
Clear codes, do a KOER/Cylinder Balance test after getting it to 185°F coolant temp and done; provided no codes are displayed.LUK/GL
 

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Discussion Starter · #7 ·
Cleaned IAC and T.B seems to be running better for now. Plunger on IAC moves up and down freely. I have a feeling the problem will continue. Plan to check codes. Noticed fresh oil at the back driverside valve cover. Could this be the problem? How do I check it for a bad gasket?

-Still have not checked wires,cap,rotor.
 
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