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Discussion Starter · #1 ·
Well my car had been running pretty well lately, but still had this annoying miss, especially at low rpms. Iac's showed to be way low. So I did the reset procedure, but when I got ready to plug the Iac back in, the MAF pipe was in the way so I had to take it off. Phone rang, didtracted me and when I cranked the car back up it immediately died. Again, and it ran for a second then thru about 13 codes as I realized I forgot to replace the MAF pipe. Put it back on adjusted tps, Iac's really high, and the car is running really terrible and missing very bad. It got dark, so I shut her down till this afternoon. Hopefully I didnt screw anything up, but I know that couldnt have been too good for the turbo. So did I hurt something, should I just unplug the ecm wire and start over from scratch? Any ideas are welcome, thanks for the help...Mark
 

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That should not have hurt anything. Go ahead and disconnect the orange wire and replug it to clear any codes that may have stored and then crank it up and set the iac.

Run the car until it is fully warm. Then put it in park and turn the iac screw clockwise to bring the numbers down to around 20. This will make the tps go up so it might be a good idea to set the tps down to about .34 or so, so it will not go out of range and screw up the idle while you are setting the iac.



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Discussion Starter · #3 ·
Steve thanks a lot, I was scared I hurt my new turbo. A couple of things though, and maybe I'm doing this wrong but when you say set the iac, do you mean "reset" it as per gnttype.org?? And turning the Iac screw clockwise, is that the same thing as the throttle stop screw?? Sounds like something different, I think I may be way off on this. I already got the throttle stop screw way out of whack I'm sure due to trying to set idle ~500 yesterday with all these problems. Anyway sorry for all these annoying questions, and thanks again man...Mark
 

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The idle speed is controlled by the chip and the ECM, you can't "set it" with the screw. Follow the directions for resetting IAC, 'til the IAC readings are right, it will idle at whatever speed the installed chip has programmed. Hope that doesn't confuse things!
George W
Raleigh, NC
 

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the iac screw looks like a throttle stop screw but it controls the base position of the iac solenoid nose.

If you have a scan tool, crank the engine up and let the car come up to normal operating temperature. With the car in Park, turn the screw clockwise to lower the iac counts and counterclockwise to raise them. As you turn the screw, it affects the tps setting. Turning clockwise will raise the tps and vice versa. It is very important to keep the idle tps under .46 volts or the ecm will run the iac plunger out and you will end up idling very fast. Therefore you may have to readjust the tps as well. Anything under .46 to about .34 is fine when the engine is running.

After you adjust the iac, turn the engine off and restart to reset the iac. Be sure it is in the range you want and readjust if required.




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Discussion Starter · #6 ·
Thanks George, I believe that clears it up for me. I dint realize the idle was controlled by the chip and ecm only. I will reset the iac until i see the proper readings. Thanks for your help...Mark
 

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Discussion Starter · #7 ·
Thanks for breaking that down for me Steve, I know these questions are a pita. BUT, that does indeed give me the answer I needed, and it is greatly appreciated. I think I will be in good shape now. Thanks!

Mark
 

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Here is something I saved, also by 'teve...

A couple of other pieces of the puzzle included (like watching out for the floor mat)

posted February 22, 2002 12:14 PM By Steve Wood
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If you look at the tps, it has slots top and bottom for the mounting screws. This allows you to adjust it properly.
Loosen both screws just enuf to be able to move the sensor with a little pressure.


Slide the sensor toward the front of the car as far as the screws will allow it to move. This should give you plenty of wot voltage. Be sure that the mat is not under the gas pedal when you try it out. Then you will have to rotate the top of the sensor back, counterclockwise, a little (while holding the bottom all the way forward) to set the idle setting. Set it, with the key on, engine off to .40-.44. When you start the car, the reading will increase about .2 v so it would be .46 if you had set it to .44 with the engine off.

If the reading at idle is above .46, it will screw up the idle of the car.

There is no magic in the numbers....40 will idle exactly the same as .46 as the ecm takes the voltage and scales it to the same number as long as it is within range. If you move it while running, the idle will change but as soon as you turn the key off and then back on, the ecm goes back to where it wants it to be.

On the wot setting, we argue all the time about the correct voltage. If you look at the chip code it does not really matter and whatever voltage you have when you have the bottom of the sensor all the way forward as described above, should be fine. I usually come up with 4.6 or so doing it that way.
Anything above 4.0 should work unless you have a chip maker that screws with the code.

To decrease iac counts, you have to turn the adjustment screw clockwise, as you turn it in, the tps will rise...that is the reason we suggest setting the iac first. Be sure the car is fully warm, in Park, no AC, when you adjust the iac. It is not an idle screw, it is the idle air control screw....
 

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Discussion Starter · #10 ·
Thanks Tim, Im gonna have to print this out
 

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I just plagiarise, thank Steve for the content.


BTW I find it usefull to copy, and paste into the notebook.
 

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Here is another one that you should have...this one was written by Jim Testa and is a good commonsense approach.

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OK, to diagnose ANY car, you need to find what you have and dont have. The way *I* usually go about it (which might not be right to some people, but its methodical and consistant so I stick to it.

1) Note the check engine light (if EFI). If its not on, STOP and find out why. Listen to how it cranks. I can pick out compression problems doing this. If you are in tune to your car, you can too. Listen to the starter as each cyl comes up on compression stoke. You'll hear the starter slow down a little at that point. You bight hear deerdeerdeerdeer, where a dead cyl m ight sound like deerdeeeeedeerdeer (great sound effects huh?)

2)Depending how accessible the intake is, I'll shoot 3 or 4 seconds of carb cleaner into the plenum. Either thru the throttle body, or the brake booster vacuum port. If its a lack of fuel problem, the car may start, it may simply kick. If it does either, its time to look to fuel system (usually, although enrighening can bring out a low sec output problem too, so dont take my suggestion of fuel as law)

3) If the car kicked, I'll put a FP gauge on it. If fuel pressure isnt in spec, now you need to see why. Fuel pump, filter, resticted line, bad reg, low batt voltage, bad relay, blown fuse etc. If FP is in spec, its time to hook up a noid light and verify our injectors are getting pulsed. If youre not getting a pulse you will want to hook up a scanner and look for RPM during crank. If you are getting RPM signal, check for spark. If you're getting spark and no fuel, although there is a commanded PW (see below) you probably have a bad ECM. How fast it cranks isnt as important as the fact you get a RPM signal. Next you'll look at Coolant temp to see if it coincides with ambient )if the car is cold), and verify TPS isnt shorted to Vref which will put the car in clear flood and cut off fuel. If these all look OK, you'll want to take a look at commanded PW.

3) If the car didnt kick, I'll yank a plug wire and see if I got spark. If I got no spark, then I'll check also for inj pulse using a noid light. If I have neither its usually due to a dead crank sensor. If I have no spark, but I have injector pulse, its usually a module.
Typically:
No start - no spark, has inj pulse -> Module
No start - has spark no inj pulse -> ECM / cam sensor prob
No start - no spark OR inj pulse - crank sensor or module

Oh, and if the module is dead, I suggest putting a coil pack on it as well as most of the module failure are caused by an overheating or arcing coil.

See, its pretty cut and dry when you go back to basics of what the car needs. Air, fuel, spark, and compression. If any are missing, the car wont run. The hard part I guess is finding out what you DONT have, then finding out why. I guess I take my experience for granted, maybe it is difficult. Kinda like Me trying to learn or diagnose a Linux problem (Right Jeremy?)

Hope this helps, and if you have any ?'s, email me: [email protected], or post them here so everyone mgiht be able to give some more.




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