My Car is running perfectly except one little thing. When the rpm's drop from driving range, 2000 +, they will not stop dropping at 800-900. The rpm's just keep right on going down to either about 200 or it just stalls. If it doesnt stall the rpm climbs back up to about 900 and is perfectly smooth. This is with nothing on, no power, no A/C, nothing. I have a PFC, will try the stock ECU tomorrow and see if that is my problem. What else can it be? Vaccuum leak somewhere? I am running out of ideas on this one.
thanks

 

Just some updates and to bump this.

I tried the stock ECU, it is somewhat better. The stock ECU doesnt die, it just has a bouncing idle that will rev between 800 and 1500 in about a 2 second cycle. I had done the ECU bypass for the A/C awhile back and undoing that seems to have helped quite alot with the stock ECU. Now the surge is only maybe 1-200 RPM total, but the PFC showed no change at all. When driving I come up to a light so about 2500 RPM push in the cluth, let off the gas and the rpm's drop like a rock. Either the engine dies or at about 200 rpm something catches and the idle bounces back up to 900.

I am wondering if this could be a TPS problem? I need to do a search on what TPS symptoms are.

 

I'm glad you posted this since I have the same problem with PowerFC and the mods listed in sig. Only really happens when cold.

Not entirely sure what the cause is but I'm starting to suspect something like the TPS combined with the Idle Speed Controller. I think Damian has a thread about adjusting both in the archives, but I'm reluctant to really give it a try w/o further diagnosing.

The odd thing is that my ISC is currently unplugged and the idle no longer drops to 200rmps or just dies. I took my car in to have the FPD replaced and when I got it back they forgot to plug the ISC so it idles low (600rps or so) till its warm. Just to be clear, I think the ISC is just under the UIM behind the throttle body. HOpe I'm right.

Do you also have a slight hesitation just off idle?

 

posting again to list sig...

 

I do have the slight hesitation just off idle, it is at about 1800 RPM I think. If I hold the idle below 1800 it bounces, if I hold it above that hesitation point it is completely smooth.

I will have to find the ISC and unplug to see what happens. Can it be reached without pulling off the UIM?

 

Re this ISC - If it is the plug that I'm referring to, yes, you can reach it w/o pulling the manifold if you have thin fingers From the driver's side, look behind the throttle body a few inches and there is a plug there that fits into the UIM at a 45 degree angle. If you unplug it, it might totally **** up your idle though and you might need to control the idle with the various idle control screws.

Re the hesitation - My hesitation is different than yours. It doesn't seem to be at a certain rpm. I just feel it kinda hiccup when i blip the throttle at idle. Especially if the engine is cold.

 

I get the hesitation if I blip the throttle at idle as well, the 1800 rpm thing is just something else I noticed that seems to be related. If I ever so slowly increase the rpm, best done with the idle adjust screw, just as the rpm hits 1800 it sputters and pops until I adjust it above that point.

What is the ISC? What is its purpose?

 

The ISC is a solenoid that lets air past the TB to control idle. It sounds like yours is sticking shut/open/ bouncing inbetween. I removed mine because it was definitely faulty and i control the idle solely by the idle screw on the front of the TB. 650idle cold, 950rpm warm. Or u can go get a brand new replacement ISC solenoid from Mazda for $397

 

Hmm, I will definately unplug mine and see if that is the problem. Thanks

 

Yeah, I read teamstealth's post a few weeks ago. It was informative. Anyone know why the ISC "stops working"? I tried to plug mine and my idle was hunting from 500-2500 constantly till I unplugged it again. It was working fine till just recently.

 

I think its j/ one of those parts that gets used enough it fails after 9+ years. Mine failed outta the blue for no reason at all. Ive never tried to "recondition" one, i.e. lubricate it and see if the action becomes smoother, so if someone wants to try that, id be intrested in the results. I know nobody wants to pay mazda $397 for a new one, lol

 

Recondition? Lubricate? Thats the first I've heard of that. Is there a way to service the ISC?

 

I'm not sure if there is a way to service them...but if i was gonna take a stab at it, id see if i could pop it open and try to clean up the seals and lubricate it with some white lithium grease or something.

 

When I try a sticking part, my reconditioning process usually involves a drop onto concrete from about 6 feet, if it fixes the problem great, if not, Oh well just another blockoff plate to make! Oh what fun.
Art

 

so back to the original question...

does anyone else's car die or have the revs drop down way low (200 rpms) when you put the clutch in when driving?

does anyone else's car have a slight hiccup when you blip the throttle at idle when cold?

someone has to have experienced this. i wonder if the title of thread isn't getting this any attention...

 

those are the same symptoms i had when my ISC went bad...the car would come very close to dying everytime i pressed in the clutch, and any change in electrical load (lights, a/c) would cause the idle to bounce between 2k-2500rpm. Regarding the dying when pushing the clutch in issue, thats caused because the ISC is closed when cruising, and when the TB closes and air is needed through the ISC, a faulty one will stick closed, killing the engine

 

Mine sometimes drops to around 100rpm and stays there but doesn't stall ever! Then it'll raise to 750rpm. But sometimes the revs will go up even more to about 1200rpm and stay there without me touching the throttle.

When I start the car in gear to disable AWS, it idles around 1200rpm till warm then drops to 750rpm. But It'll just go up again when it wants to!

Damn this idle problem!

 

hey what exactly is the isc and aws. This is the first i've heard of this so I need to be absolutle sure what i'm looking for. Also is this for a TII or NA.
your help would be greatly appreciated, Thanks.

 

It is different on an FC.

ISC = idle speed controller
AWS = accelerated warmup system (or something like that)

Do a search for exact definition.

 

I unplugged the ISC and now it rarely dies when I push in the clutch. It still often drops pretty low, like maybe 500rpm but that is only about 10% of the time and maybe 10% of that will it ever die. i guess I need to tear into the ISC and see what I can find.
thanks for all the help!

 

I have the same exact problem.How do I unplug the ISC?

 

radiantrx7

 

I dont know how I signed in as Urai???

 

I've got a PFC and 90% of the time when coming to a red light and I push in the clutch from >2000 rpms the idle will drop down to about 300-500 rpms for a split second, then jump up to normal idle.

I've even adjusted the rpms that the injectors are supposed to turn back on from decel to like 1500 rpms but still does that.

Also noticed sometimes when cold there's a small hiccup when tapping the gas from idle.

 

My symptoms are identical to original poster. My only dies when it is very cold though. Tap the thottle of idle and it stutters for a split second before the rpms shoot up. At that moment it also reads a little lean. If idle is 12.0:1 then right when I hit the gas from idle it will go to around 14 or 15:1. If I log this event is lasts around half of a second. I have just learned to live with it, but if replacing the isc will fix it I would replace it.


Matt