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Idle Adjustment By Darrin Tebbe (on Corral.net)

It seems that many people have trouble with the way their 5.0 Mustang idles. Symptoms are usually a stumbling or rough idle which may be the result of modifications, or any number of other factors that may contribute to the problem. Clogged Emissions Gas Recirculation (EGR) Valves or Idle Air Bypass (IAB) solenoids are often to blame. A bad Throttle Position Sensor (TPS) will cause the engine to "hunt" for a proper idle setting. If you are experiencing idle problems first check the IAB. If it has large amounts of carbon deposits in it you may need to clean it using regular carburetor cleaner. You will have to remove it to do this, DO NOT clean it while it is on the car! If you have checked to make sure that your EGR, IAB, and TPS are clean and properly set and you are still experiencing problems try the following:
1. Clear the EEC-IV's idle memory by disconnecting the battery for 20+ minutes.
2. Disconnect the Idle air bypass solonoid
3. Reconnect battery
4. Start engine and set idle speed to desired RPM with stop screw on throttle body (900 rpm works great with E303 or larger cam)
5. Turn off engine and reconnect the air bypass solenoid*Optional -- set TPS to 0.90 - 0.95 volts (Do not exceed 1.0 volts MAKE SURE!) Use a digital volt meter!
6. Start engine and let it idle for 2 minutes with no accessories on.
7. Turn off engine for two minutes
8. Start engine again and run for 2 minutes with every accessory turned on.
9. Turn engine off again. Your computer should have now re-learned the new idle settings. This procedure assumes that you have a clean IAB valve. If it is carboned up then you may need to remove it and clean it with carburetor cleaner.

F.Y.I.:
For people that dont know you have to take off the neg. battery cable first and always put it back on last when disconecting both battery cables.
 

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I disconnected the neg, pulled and cleaned the IAC. put it back and my car idles much better and seems to run smoother too. Prior to resetting the computer I had a dirty IAC, and a massive vaccum leak.
 

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87vert said:
the most recommended tps setting is .98
what wires do i test to get that reading? the org and black wire i got a reading of about 5v and with the org and grn wire i got a reading of about 4.03v.. so wht do i need to do to get .98v
 

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cali has asked my question do i put one lead in one wire and one in the other with a digital multimeter? and im guessing low low dc on the switch?? thanks im slow you got to work with me. take care

matt
 

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I posted awhile back requesting help with fuel pump power problems on my 89 5.0 and there were quite a few great posts that had tons of tech and ideas for troubleshooting. Well, I followed most of the posts and checked and/or replaced damn near everything including fuel pump, regulator, fp relay, computer, TFI, ig. switch, and stripped all the wiring and checked fuseable links and whatnot from one end of car to other including the inertia switc. Problem still persists, cant get power to fuel pump w/o jumping the test connector fp lead. Just was wondering if anyone else has had a similar problem, and any ideas how to fix I might have missed. Been driving for months now with the jumpered wire powering the pump with real lousy fuel mileage, also get the cel on after car warms up, varies on when it comes on tho.... Even had the o2's relocated thinking they were hitting the front crossmember with vibration, but no good on the cel there. Any help would be greatly appreciated.
 

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the most recommended tps setting is .98
which is a BS myth... as long as the voltage is btween .5 and 1v, the EEC could care less what you have it set at
 
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