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Location:
Lost in the K hole
Registered:
May 2002
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 7m idle problems, and more...!!
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Tue, 16 December 2003 13:24
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-recently rebuilt toyota 7mge 3.0L (currently 250km old)
-10.7:1 compression
-mildly altered cam timing (stock duration and lift)
-about 25deg ign advance
-stock everything else (for now)
first off: from the very get go of the engine's life, ive had serious problems with idle. when you start the thing, she's fine, and will happily sit on 1k rpm without wandering, nice and smooth... BUT get going, and then slow back to a stop, and when the revs fall, they fall below idle, and it either stalls immediately, or wanders up and down from 200-900rpm threatening to stall. this happens 100% of the time when slowing down from any kind of driving, engine hot or cold...
ironically, if i have to restart her from such a situation, she'll immediately go back to a nice smooth 1000rpm stable idle...
second problem - and this is weired... say im sitting stationary and in neutral. i rev the engine gently up to say 2.5k rpm, then slowly/gently let the revs fall back down... as the engine passes through about 1800rpm she suddenly 'fails' : the revs drop drastically to 1000 rpm, then raise back up immediately tp 1700rpm. this occurs 100% of the time ive done this. once again.. WTF?...
other than these two issues, everything else is just fine!!
im buggered if i know where to start!
thanks gus!
ed
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Location:
Brisbane
Registered:
July 2002
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 13:28
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I'd be starting with the throttle position sensor.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 13:39
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Yeah, good start (thou I'm sure Ed's checked that)
Did you clean/test all the sensors before you put the motor back together?
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Location:
Lost in the K hole
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 13:39
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| clancey wrote on Wed, 17 December 2003 00:28 |
I'd be starting with the throttle position sensor.
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checked it already 
but funnily enough, the readings are within range no matter how i set it on the throttle body... meh, i got no idea 
ill mount it to both extremes tomorrow and see if it does anything...
maybe the o2 sensor?
timing somehow?
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Location:
Brisbane
Registered:
July 2002
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 13:50
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Start the car and have a play with the sensor loose  You could also test the resistance over the entire range and see if there are any points where the resistance jumps to an unexpected reading.
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Location:
Melbourne
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 13:55
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get a spare idle steper motor and plug it in watch to see if its opening and closeing as it should, if it does put that in see if it solves the problem, also i know gte's have a backfire protection valve for it make shure thats in the right way,
do the same sorta thing for the tps.
Does sound like a ISC issue tho!
Allan
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Location:
Melbourne
Registered:
May 2002
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Location:
sydney
Registered:
March 2003
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 21:32
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u can try to reset the idle motor
this is done by reving the engine over 1400 rpm for about 4 or 5 mins
this will move the idle motor in and out to find its limits
then the ecu will try find the correct idle again after the 4 mins
another thing to check is make sure u have bled the cooling system properly im sure this wont be the prob but it can cause idle probs if u have air in the cooling system especially if the cooling hoses go thru into the throttle body
otherwise check for air leaks and shit like that
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Location:
Lost in the K hole
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Tue, 16 December 2003 23:47
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hmmm, interesting statemtent about the cooling system...
ive actually disconnected the coolant hoses from both the throttle body AND the ISC... i didnt think that the heat served any purpose short of preventing internal icing... perhaps the ISC needs coolant running through it??
might pull it off and give it a clean, and try that reset thing...
hmmmmmm
still doesnt explain that crazy drop in revs when descending through 1800rpm though 
cheers
ed
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Toymods IT Secretary
Location:
Oz
Registered:
June 2002
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 00:55
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Hi Ed,
There is an explanation for the "crazy" drop It's called idle speed cut. The ECU, when it thinks it's at idle (ie IDL and E1 or E2 shorted through the TPS), will cause idle cut when the revs are above a certain point (eg 1800rpm). Once they drop below a certain point (like 1000rpm) the ECU restarts fuel/ignition delivery.
If the situation is not remedied it will happily bounce between those two values as was evident in Max's 1G years ago when the ISCV was fully open and wasn't shutting - block the air supply lines and everything behaves.
You *MUST* set up the TPS. There's no such thing as mounting it at either extremes to see the effect For the idle circuit to operate correctly the TPS idle switch has to see the closing of the throttle, and the rpm has to be within tolerable limits.
The factory procedure is to use two different sized feeler gauges between the throttle stop screw and the stopper to open the throttle a certain amount. With one thickness the IDL switch should be closed, with the larger thickness the IDL switch should be open. I have found that setting it up by "feel" (ie. determining the closed/open transition by hand) doesn't work as well as using the feeler gauges.
In some cases you can set the TPS to a position where the IDL switch never closes; in such a scenario the ECU will think the engine is never idling, but running at a very small throttle opening. In some cases this is needed when the engine wont idle properly in the idle state (yours may fall into that category due to the standard nature of the components  )
Your ECU does not have a stop light input so that can't affect the idle either (with some ecus all weird idling/roughness magically disappears after connecting that input).
I actually don't know what the coolant lines do on cars with stepper motor ISCVs. With other types of ISC the water lines take care of cold start idle up, but I don't know for sure if this is the case with the stepper setups - the valve has plenty of range to allow enough air in.
So set up the TPS correctly, and then diagnose from there.
HTH.
Mos.
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Location:
Melbourne
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 01:45
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No heating on my throttle body or ISAC valve idles perfectly 
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Location:
Lost in the K hole
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 03:38
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| Mos wrote on Wed, 17 December 2003 11:55 |
You *MUST* set up the TPS
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champ mos, thanks.
i have set the tps according to TSRM guidlines (feeler gauges between the stop screw etc), but as i mentioned above, even mounted at both extremes, the readings are within the manual's range. ??
im suspecting the TPS might be dodgy, ill pull it off and go right through it looking for output issues (that could also explain the error 51)
this would explain the idle cut  *phew*
would it alos be responsible for the hunting idle? It does sound more like an ISC issue to my mind, but id appreciate your input...
cheers
ed
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Registered:
August 2002
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 06:08
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Just as a matter of interest......my 2jzge likes to idle at about 1800rpm when first turned on, then slowly drops down to normal idle of about 800-900rpm once warmed up.
Any ideas?
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 06:11
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AFAIK Glen, thats factory ECU or ISCV working properly.
I know my 5MGE does it
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Location:
Lost in the K hole
Registered:
May 2002
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Re: 7m idle problems, and more...!!
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Wed, 17 December 2003 10:02
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yep, mine sits on about 12-1300 rpm, then drops down to 8-900
ps - problem fixed, was the TPS (wasnt making good connection with the loom plug...)
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