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I have a different idle condition on a 331 stroker motor with Anderson cam, trick flow heads and GT40 upper and lower with full catted Basani exhaust and full MSD distributor and box. Also I run an A9l ECU. I have set and reset the idle and it works fairly well when sitting still. The ECU has learned fairly well the difference of no accessories on and everything running. It likes about 800 RPM which is OK since the cam and aluminum flywheel add to an idle problem. NOW. here is the issue I have . When rolling, you can push in the clutch and coast and the idle stays at about 1400 RPM. So, when you let off the gas, you are still pulling at 1400 RPM. This causes bucking and rough running. I just changed the VSS sensor thinking that maybe that was the problem, but nothing changed. I run 3:73's, so there is a "WHITE" speedometer gear. I think that gear is a gear that is used to try to make the speedometer work with 3:73's. Could that gear be fooling the ECU as to the speed of the car? The high idle when rolling is annoying and causes driving issues. Any thoughts ?
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Iac issue. Have you cleaned or replaced it? When you reset the idle is the car completely warmed up? The ECT stable condition must be met before setting the idle. -
Check electrical connections at the transmission and also the neutral safety switch at the clutch quadrant.Comment
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Fox High Idle.
Yes car at full operating temperature when idle set. Also, the clutch switch is no longer in the loop. It has been wired around. Now the car starts with the clutch in or out like cars in the past. I was told by a technician that the clutch switch was not critical on the older Ford ECU's. The Newer ones it is different and has to work as it came from Ford in order for the computer to function properly. I sat last night and let the car idle for 45 minutes after being driven, and the idle sat perfectly on about 800 RPM the whole time.Comment
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I've been dealing with similar issues after putting mine back together with a similar build. Just throwing out places to look in areas that you sound like you've been working on. According to my research - vac leaks, grounds, IAC, wire harnesses, and base idle reset procedure seem to be the places to look.
I'd try cleaning the IAC as mentioned and go ahead and clean the MAF and throttle body while you're at it.
Hopefully someone chimes in on eliminating that switch... I watched a video somewhere online where the guy unplugs it at the transmission and the car dies. He was proving the point on how critical that circuit is to make the car run right.
I'm curious to know what ends up fixing it.Comment
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JV106, the IAC is new as are both sensors on the intake manifold. I cleaned the mass air and installed a new TPS. The TPS is set at .98 volts at closed throttle. Ihad a TFI module go bad, so I have a new "Genuine Ford" TFI installed. We did a smoke test and had no vac leaks. Crusing at highway speed with no load, and the vac gauge reads about 15 inches. The fuel pressure holds at 38 PSI at highway speed. Don't get me wrong, the car pulls very good and will boil the tires in 3rd gear when you get on it. Also it is an 8.7 compression motor. I run only 93 octane, and have the timing set at 15 degrees, and I have no detonation. I may replace the little plastic rod on the clutch pedal (why yhe switch is by passed) and see it that will help. Who knows at this point. Funny, the car gets about 23 MPG if you hold it to about 65 on the highway.Comment
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I read somewhere one time that a guy contacted Anderson and they told him to set the TPS at 0.6V...? Good luck.Comment
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Anderson Motor Sports Comment on TPS
Worth a try. Could be that with the cam specs, the TPS needs to send lower voltage to the ECU. Worth a try, and easy to do.Comment
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Fox Idle Issues
OK, so I went back a re set of the base idle with the spout connector out of the plug. Reset the TPS to .90. Installed a new VSS sensor just in base. The idle settles down to about 750 RPM after about 30 seconds. Operating temp was at about 190 degrees when the base was set. (Turned off electric fan in order to get above the 180 degree thermostat) As per the instructions, I set the base idle with the set screw at about 650 RPM. Now the problem. The car still will idle at 1500 RPM as long as the car is moving, even with the clutch held in or even coasting in neutral. As soon as the car stops rolling, the idle settles down to about 750 RPM, which is OK with the Anderson cam I am running. What's next ? change out the radio antenna ? (LOL)Comment
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Is this an original 5speed car?--carlos
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Fox Idle Issues
Yes it is an original 5 speed car. Regular transmission, but does have 3.73 gears . Have been running the "WHITE" speedo gear that I was told would be the one needed for the 3.73's. I have replaced the gear two times when doing a clutch job. The gear was partially stripped both times, but the speedometer works fine. There is no jumping of the needle. I was told that since Foxes did not come from the factory with 3:73's that there is really no "Right" gear available, and the white gear is as close as is possible to find. Any truth to that ? Could a wrong gear cause the VSS sensor to send bad info to the computer ?Comment
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Are you 100% certain that the wiring harness and ecm are from a Fox mustang and not an SN95 piece? You can slide the ecm out and look at the code to verify. It sounds like the decay rate needs to be adjusted along with the % airflow for the IAC. 94-95 cars are known for this and because of that they either get a tune to correct it or people put restrictor plates behind the IAC to limit the amount of airflow. The cars are old so you never know what previous owners could have done.Comment
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What happens when you lug the car down below 1500 in gear while moving? What about holding the throttle open for a period of time while still and quickly letting off? Does it drop back down? I've seen cars that'll hold the idle high while moving but drop at a stop.Comment
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Fox idle
The ECU is a 9AL . Original harnesses.Comment
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Gd i dont miss that shit. Save up and rip all that shit out of the car, install a real ecu setup like a big stuff or a FAST, and never look back.
Till then, get an iac bleeder and adjust it till it is at least tollerable. I never got rid of that idle problem till i tore the ecu out of the car. If you ever got a blower, you wont want the stock pos ecu anyway.Comment
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