Misfire around idle

[Fubar231]

So im having a random miss (not all the time) at idle and around 700 rpm. My car idles at 450-500 and im going to check my idle control valve tomorrow with a ohmeter thing. I heard its suppobsed to read 10-30 ohms of resistance. Or whatever that symbol ment. Im worried though that if the ics valve is bad, and i repalace it is it will fix the miss. Could there be other things that could be causing this? Bad spark? The cars fine 1500+ rpm but it has a random miss below 1000.

[bgrieger]

a little miss every couple of seconds is very common. It's not the way it is supposed to be, but I can't remember hearing a 7m in over 10 years that didn't have a little bit of a burble at idle. I've seen one that went through a complete rebuild, went standalone EMS after various piggybacks and anything else you could think of and it did it without fail all the way along. He just went 1uz with big cams though, so when I hear it next I know that at least it was suposed to sound like that

[Jeeves]

It's not the way it is supposed to be, but I can't remember hearing a 7m in over 10 years that didn't have a little bit of a burble at idle.

+1

[CRE]

Pretty often thoroughly cleaning out the ISC and it's plumbing can help lessen this. If you look at an AFR gauge you'll see that the 7M doesn't hold a steady AFR very well at idle. I've tuned my MAFT Pro for 15.2 at idle and it's the most stable I can get... actually, it's pretty good, very little inconsistency.

The low idle speed needs to be addressed, as you know. That's not normal.

Here's info on testing the ISC: http://www.cygnusx1.net/Supra/Librar...ction=FI&P=106

If you take it apart to clean it there are two sides to it. The stepper motor and the valve. Carefully take it apart and clean out both halves carefully.

[Fubar231]

THanks for the info guys. Im cleaning the ISC tomorrow. I metup with a guy from ohiosupras.org today and we went over a few things. The shop had my timing set at 15degrees! I was like jesus! So we put that down to about 11, but the line wasnt stable really. After i clean the ISC were going to hit it with the timing gun again. What other than the ISC could cause a low idle? He was saying something about throttle screw and if its been messed with and such on the throttle body.

[Jeeves]

Originally Posted by CRE

If you look at an AFR gauge you'll see that the 7M doesn't hold a steady AFR very well at idle.

I'm not relying on the Maft Pro for Idle AFR control, but with TCCS managing it, I've got damn near perfect 14.7 AFR's at idle. :shrug: Ducks a little up, then a little down, but it almost always hovers at 14.7.

[CRE]

A 5º bump to the base timing is NOTHING.... sheesh. The way you reacted to that, you'd $h!t if you saw mine.

Ignition timing isn't your problem although the mechanical timing may be off... Not the most fun thing to check and reset. Do not go by the harmonic damper unless you verify it's accurate. They can slip over the years putting the timing indicators out of alignment and thus give you a false timing reading. Mine is off by only about 2º but I've seen one that was off by just under 10º.

I'm not saying he doesn't know these cars well, but even with a mentor, double check everything the two of you do to the car... he should know that +5º isn't an issue on even moderately modified 7Ms. Hell the N/A's don't really wake up until 17º - 20ºBTDC.


Hey Jeeves, I sent you a PM. Long time no see. I suspect part of the inconsistent AFR with my 7M-GE were due to the VAF... ick... and possibly a clogged injector. I don't mind running with a lean idle though... saves a tiny bit of gas and it is stable. I thought you were running PTT in your setup?

EDIT: With the TCCS controlling my idle I'd see a rather consistent fluctuation from the upper 16's to the the upper 13's. With PTT it stays in the mid 15's.

[Jeeves]

I normally run my base timing at 14-16deg. With my plans here to run timing control (@CRE, yeah, I got the PM, I was dashing out the door and hadn't gotten a chance to write a reasonable reply yet ) I should be able to figure out where my beast wakes up.

[CRE]

I should probably note that my unsteady idle AFR was back before I started modding the air metering system and started tuning. So, something may have been amiss which I never got around to fixing. 15ish still feels the smoothest though. I see my AFRs stay around 15.2 to 15.8.

On a side note: I've read the turbo tends to mix the gasses and generally results in smoother AFR readings. It's pretty consistent with what I've seen from working on both. Not a HUGE difference, but noticeable enough. Anyone else ever notice this?

[Jeeves]

I've never worked on any NA's so, I've got no input to give :-/