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Discussion Starter · #1 ·
90 Pony 4spd. Rev's up to max at start up. Replaced Throttle Position Sensor. No help. Replaced ECM. No help. Only way to be able to drive it w/o burning up the clutch (just rplaced) is start car, when it rev's up, turn off key.
Just before motor dies completely, turn key back on, and it idles and runs fine. It will at times rev to max when stopping at intersection, but not often. Almost always does this at start up.
HELP PLZ
 

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Discussion Starter · #2 ·
Further information

Not being much of a shade tree mechanic, I will describe my latest discovery. There is what appears to be a type of injector positioned above the bore of the throttle body. When I start the car and let it Rev..... this injector?? is spaying fuel at an alarming rate. The butterfly remains closed???
WTH is going on w/ this thing. Again I am very limited at best as a fuel injection mechanic. I have a chiltons for this car, but am unable to determine even what this part (injector) is??? Help
 

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The injector thing is the actual injector. This system has been decribed as an electric carb. Since you have the chiltons, try pulling the codes if you can. There is a section that explains how in there. Look in the emissions section.

And welcome aboard to the site :D
 

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Discussion Starter · #4 ·
More info

Ok, I removed the Idle air control, and disconected it from the loom. then reset the idle. and wahla, it runs and starts fine. Not sure if this will be an issue when weather turns cold, but for now, at least my 17 year old can drive it again w/o my worrying about it blowing sky high. Any further suggestions on why this is happening would be appreciated.
Thx
 

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Well, it's probably just the IAC motor itself. You can disassemble it and clean it, and that will usually fix it for a few more years. I wouldn't run it without the IAC, because you're going to suffer stalling on cold startup.
 

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You'll also deal with stalling out whenever backing off the gas quickly. The ECU doesn't adapt quickly enough, which is why the ICM is there. My car idles worse with the ICM connected, and never hits the idle screw. Without the ICM it's perfectly smooth, but I'll have the stalling problem whenever I let off the gas. I tried it on the highway, and that wasn't the most fun, so I deal with the junky idle.
 

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Discussion Starter · #7 ·
Ref more info

Well, it's probably just the IAC motor itself. You can disassemble it and clean it, and that will usually fix it for a few more years. I wouldn't run it without the IAC, because you're going to suffer stalling on cold startup.

You'll also deal with stalling out whenever backing off the gas quickly. The ECU doesn't adapt quickly enough, which is why the ICM is there. My car idles worse with the ICM connected, and never hits the idle screw. Without the ICM it's perfectly smooth, but I'll have the stalling problem whenever I let off the gas. I tried it on the highway, and that wasn't the most fun, so I deal with the junky idle.As earlier stated the IAC or ICM has been replaced new. The ECM was replaced w/ rebuild or reman. So I am stuck trying to find the reason for this.
With some help from my 17yoa son (at last) I was now able to see that the IAC/ICM is pushing the throttle partly open at shut down. when I use the little trick mentioned in previous post to get the car to idle properly, then turn off the car. I can watch the IAC/ICM first retract, but then a second or so after car is off, it then pushes back at least half way open. Thus the next time you start the car....... super hi REVs??????
So, thought I'd give it a shot and remove the IAC/ICM. Runs great w/o it but would put it back in place if I can fix the cause of the trouble.
Sorry I'm long winded and a PIA, But Last car I really dug into and fixed all myself was my 68 Mustang. Even this 90 is too new for me to understand.
Thanks
QTRHOSS....... aka Old School
 

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The ICM keeps the throttle partly open after shutting the engine off for restarting purposes. Think of it acting like an automatic choke. It shouldn't be pushing halfway open, however. I doubt it's the ECU, as I've never personally seen one go bad, but have heard about it once or twice. It might be the contact button the new ICM. Definitely pull the error codes, all you need is a jumper wire and you can watch lights flashing inside the car to tell the codes.

This car isn't that advanced beyond your mustang, only that it has a few more electronic controls, half of them for emissions. The other option is to check the wiring harness to the ICM, and the wires from it to the ECU and see if there are any breaks or bad connections. If that passes, then it could be a faulty ICM.
 

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Well actually you didn't mention replacing the idle motor, but since you did: Do you still have the old one? If so swap it and if you have the exact same problem, then it's not the motor. Also, let's get a full history, with the sequence of problems and replacements.
 

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Discussion Starter · #10 ·
Sequence of events

Sorry, I misnamed part I replaced first. Advice was to replace ICM. Did so. No help. Next was told code showed bad ECM. I don't know the code number. So I ordered a reman ECM and replaced the original. No help. Got a Chiltons #7055 for 1981 - 90 Escort, Lynx, Tempo, Topaz. Didn't really see any diagram that looks like what I have in there. Finely got my son (bought the car for him) To help. Was now able to see what went on as key was turned on and off, Started and shut off. ect. See previous posts. Thus removed ICM Just to see what happens. Damb thing runs. still no idea what causes the ICM to do what it does.
 

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The ECU runs out of juice within ten minutes of disconnecting the battery...no discharge needed that I know of. Usually less time was required, unless the system had an airbag.

QTRHOSS, have you personally checked for error codes, or had your son help? Do a search in the 1st gen section, about ECU error codes, and you'll find the method on how to test. Basically, all you need is wire and to wash the flashes of the check engine light, or in 89Harper's case, the upshift light. Once the flashes are put together, you can read the codes stored in memory, and see what the ECU is telling you. It might be O2 sensor related, maybe throttle sensor not registering properly. Could be the ICM circuit. If you don't understand, just ask questions...get your son in on this so he can learn. He might understand the terms more if you don't. We'll get this. I'm going to start work on a specific how-to, and perma-link it in my signature, for ECU error code checking...it might take me a little while, though. Still, that'll help everyone get the needed info.
 
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