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Location:
Canberra
Registered:
May 2002
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AFM 4AG idle problem (long)
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Sun, 09 June 2002 09:38
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For those that don't know, ever since I did my SC conversion, I've had an idle problem. Today I decided to track down and find the problem. No luck..
The idle continually bounces over about a 1000 RPM range around once a second. It's bad when it's cold, then seems to get a little better, but, it's never spot on. When it's just about at normal operating temperature, the downward dip in the idle is low enough that it will stall.
I've checked for vacuum leaks - None.
I've checked the timing - It's spot on.
I've set the TPS according to the BGB.
I've tried it with and without coolant running to the TB - No difference.
I've replaced the vacuum lines around the ABV - Seemed to help a bit, but, no real improvement.
I've checked the Idle motor - It come in within spec.
I've tried another idle motor - No change.
I've replaced the ABV - No difference.
I've blanked off the ABV - No difference.
I've blanked off the idle controll motor - This was interesting, the throttle was really initially sluggish, then suddenly the motor would jump to around 2000, it was really hard not to get it bouncing. Obviously the idle motor is doing a pretty good job. This was what led me to start looking at the ABV, I thought it might be sticking shut then suddenly opening - Apparently not..
I've fiddled the mixture screw on the AFM and checked the AFM, it all seems to work OK.
I've tried it with every vacuum hose I could get my hands on disconnected, with the supercharger unplugged, even with the idle motor unplugged. There were some differences, but, generally, it seems to have the same underlying problem.
I'm starting to run out of options here - I've got a Haltech, but, I'd really like to get it running with the factory computer for as long as I can.
Sorry about the length, I just wanted to make sure I've covered everything.
Has anyone got any suggestions? Even any more avenues to explore?
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Location:
Western Sydney
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Sun, 09 June 2002 09:48
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Hi
I have heard of this problem affecting quite a few gze owners. Some have said it appears to be a fault from the factory that was never fixed. There was a thread about this on the club4ag forums, but this going back well over a year ago. I can't remember if there was a soultion.
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Formerly TRD_RoLLa
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Sun, 09 June 2002 10:33
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Hey whiteGZE did this occur on MAP gze's?
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Location:
Colyton, NSW
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Sun, 09 June 2002 11:56
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i had the exact same problem.
idle up.. then down.. then up.. then down... and then stall.
i changed the oil and spark plugs... all ok after that...
or was it a new exhaust...
on of the 2 deffinately
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Location:
Sydney, Australia
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Sun, 09 June 2002 23:17
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Have you checked the ECU diagnostic codes?
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Mon, 10 June 2002 01:28
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No error codes from the ECU.
It's had two oil changes in around 1000km (new motor) and it also has new plugs and that hasn't changed anything...
I've got a new muffler on the way - Perhaps a new exhaust will do something?
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Location:
Newcastle
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Mon, 10 June 2002 11:43
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just a possibility try fitting a few more throttle return springs, if the supercharger is blowing the air in it may have a weak spring which causes it to open a bit then close again.
just a thought
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Location:
N.S.W
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Mon, 10 June 2002 13:47
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My mate has the exact same motor in his ta22 and it does exactly the same thing. It seems like it will never be fixed. God when it idles at traffic lights like that it becomes very annoying!!! He has tried replacing all the vacumn lines, got a new aif flow meter and it still hasnt fixed it. I will get him to try the return springs as mentioned, if only it is something so simple!!!
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Mon, 10 June 2002 21:57
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| Celica_RA40 wrote on Mon, 10 June 2002 9:43 PM |
just a possibility try fitting a few more throttle return springs, if the supercharger is blowing the air in it may have a weak spring which causes it to open a bit then close again.
just a thought
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Nice idea, but, I've had my hand on the throttle linkage while it's been idling and it definately doesn't move.
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Location:
N.S.W
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Tue, 11 June 2002 11:33
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yeh I put a extra return sping on, and it did nothing. Any other ideas?
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Location:
Newcastle
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Tue, 11 June 2002 11:41
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get a stoichometric reading at idle ( air to fuel ratio) it should be 14:1
if it isnt that the AFM metre could be out and all that is required, is the adjustment of the spring. if you know how maybe tighten up the spring by about 5 notches( i know it is a lot) and see if it still has the same problem, this is leaning up the mixture a bit, make sure you mark the original position with whiteout before moving te wheel.
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Location:
N.S.W
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Tue, 11 June 2002 12:46
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ok how do i check the air fuel ratio??? Anyone else have any ideas on how to fix the problem???
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Location:
Newcastle
Registered:
May 2002
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Tue, 11 June 2002 22:05
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Twinky - Your mates car, does it have the oxygen sensor located the standard distance from the engine, or is it further down the pipe (like mine)?
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Location:
Newcastle
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Wed, 12 June 2002 08:32
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if you guys are running a cat convertor is the O2 sensor before or after the cat? because the O2 sensor should always be before the cat convertor, another thing you might want to try i see if the O2 senson is working by testing the voltage it is putting out. from memory it should be about 0.1 to 1 volt
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Location:
N.S.W
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Wed, 12 June 2002 08:53
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yeh its a bit further down since its has rear wheel drive extractors. But yeh its before the cat, he only just got a cat recently. I'll try checking the o2 sensor and hope it works, cause its been doing the weird idle for about 4 months and its really starting to piss him off.
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 01:48
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I'll try to find the time to do a bit of oxygen sensor relocation this weekend.
Celica_RA40 - It is currently before the cat, but, a fair bit further down the pipe than standard. I get the feeling that the sensor I'm using might be reading a little off as well.
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Location:
Perth, WA
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 05:06
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Ben,
Its your intercooler that is causing the problems.
The standard top mount cooler is both small, and has a short intake tract. the bigger the cooler and the longer the intake tract is the worse the problem is.
The idle system is a feedback system, and the intercooler causes a time delay to be added to the system, which can cause the system to become unstable. This causes the idle problems.
Think of it this way.
The IC is after the throttle and is therefor basically and extnetion of you intake plenum. At idle, air flow is very low, so to consume this much air takes time, a lot if time compared to when u are fanging it.
The idle becomes low, the ECU opens the idle control a bit, but because the volume after the throttle is so large, this tiny throttle opening takes a while to have an effect. The revs keep dropping more so the ECU opens it more, still takes time to get there and the revs drop more. The ECU opens the idle again. The first increase in airflow coming through from the first idle control opening gives the motor some air, the revs rise back to the right position so the ECU closes the idle down a bit.... Too late because it already allowed a shit load of air in before, and this works its way to the motor. The revs rise with all this extra air and become too high, so the ECU closes the idle valve. The revs keep rising because of all this air... then the horrible cycle repeats but in reverse of what i have described.. the revs drop down and when they are right, the ECU opens the idle a bit.. but it has no immediate effect, so it opens it a bit more.. and a bit more... and it just repeats over and over and over.
This is why i fitted a Subaru water to air intercooler to my ae86 with GZE to keep this problem to a minimum, but it still did it a little bit. One other solution is to fit another throttle AFTER the intercooler...my runs perfect now as i have a RWD 4A-GE inlet manifold and am running a Turbo. Rock steady idle even with the original computer, as the ECu does not control my idle anymore.
MAP gze's do not do this anyware near as bad. I hav not got my head around this properly, but its just a fact that they are better... maybe less gain on teh feedback loop to the idle control??
Cheers
Mike
PS. If you dont have a cooler then i dont know what the problem is..hahaha and i wasted 10 minuites of my time.
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Location:
Newcastle, NSW, Australia
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 06:57
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Spot on! Couldn't of said it better myself.
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Location:
Western Sydney
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 10:24
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Excellent response AE86_Sprinter. Your logic is sound. 
I'm not a big fan of the throttle before the sc setup but I guess you have to look after the supercharger.
I have fitted a front mount intercooler in my corolla and the piping is quite long to say the least, not much you can do to make it shorter unless you fit a water/air intercooler as you have done. I don't experience any problems with idle, though mine is MAP.
Something I noticed when I first fit the front mount is that when backing off the throttle to change gears, the revs still increase for a split second due to all the air still remaining in the pipes. I only notice the problem now if the engine is cold.
Another thing that is definately no good if you have a front mount with the gze engine (long pipes) is that you are effectively starting the car at full throttle.
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Location:
N.S.W
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 12:42
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my mates has the standard top mount intercooler still, but it is mounted over near the battery and has longer piping. So would this be enough to cause the problem? When he first got the car it never had this problem. How could i tell if it is the problem?? Take the intercooler off and bi-pass it with a bit of pipe??? Would it die in the arse if it didnt have a ic??
Thanx
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Thu, 13 June 2002 22:04
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Mike - That sounds to be a logical idea. The intercooler is an aftermarket ARC unit out of Japan, I know of one other person using the same cooler without a problem, it isn't massively bigger than the stock one either..
It is worth looking at though.
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Location:
Newcastle, NSW, Australia
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Fri, 14 June 2002 06:20
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Don't know about "aftermarket". Looks like a modified Nissan intercooler to me.
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Location:
Canberra
Registered:
May 2002
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Re: AFM 4AG idle problem (long)
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Fri, 14 June 2002 14:11
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That is what ARC sell you when you buy an AW11 cooler from them. There is a lot of custom welding on it..
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