So I'm dealing with some Idle issues as described below. Next step is to check, clean, rebuild or replace the AFM. Specific question: Can I use a USDM AFM from an AW11-GZE
Thanks, Mo

Don't flame me, I did my searches
My setup: USDM '87 AW11 with JDM 4agze from AE-92 Levin. AFM. Distibutorless twin coil ignition. Swap done in 1998. Got about 40K miles on the engine. Car runs beautifully with exception listed below.
Symptoms: On occasion, while idling, rpm's will drop below 600 or so and the car will stall. (Starts right back up again.)
I have tried: Replaced ECU, igniter and coil pack (All JDM), checked grounds, doubt it's a vacuum leak (I have a vacuum/boost gauge). Cleaned throttle body.
Wondering if it could be my AFM going bad? Is the AFM the same for JDM and USDM?
Also wondering about the IACV. Notice that on mine the vacuum hoses are blocked off. As I say the car has run thousands of miles this way.
I am NOT a mechanic, but have spent many hours on this car. (Had it since '88).

These symptoms got really bad a while ago, and CEL threw an "igniter" code, that's why I went through the diagnostic flow and checked/replaced all the ignition stuff listed above. After going through all of this I also flushed/replaced the coolant, cleaned up some wiring issues etc, and the symptoms occur much less frequently now.

I want to get the bottom of this. Help!

Does the problem occur at all engine temps? What is your idle vacuum? Have you checked your cam and ignition timing? If your cam(s) jumped a tooth..... Crank and cam bolts torqued properly? I had a loose crank bolt and the key between the sprocket and crank broke, and the sprocket slot got worn wider. Caused similar symptoms. That was with an N/A.

What rpm does the engine normally idle at ?
How does the idle get down to 600 rpm ?
Does it suddenly drop from 800 or 900 rpm ?
Or does it slowly idle down until it gets to 600 rpm and then choke ?

There is a IDL switch inside the AFM that is held closed while the
air passing thru the AFM holds the flapper open. If the airflow gets
too low, the flap gets so close to being closed, that the switch open
circuits (removes a ground), the fuel pump stops and the engine
stops because it is not getting fuel

It could be that the AFM is shutting the engine down, but that does
not explain why your idle drops to 600 rpm.

Cheers... jondee86

Thanks for the reply. Tends to happen when hot. Recently adjusted valves and made sure crank bolt was tight. Engine runs too sweetly 99.9% of the time for it to be a major timing issue. Gonna follow up with the AFM. I'll post results.

sirdeuce wrote:Does the problem occur at all engine temps? What is your idle vacuum? Have you checked your cam and ignition timing? If your cam(s) jumped a tooth..... Crank and cam bolts torqued properly? I had a loose crank bolt and the key between the sprocket and crank broke, and the sprocket slot got worn wider. Caused similar symptoms. That was with an N/A.

Hi. Appreciate the reply. I've got the idle set a bit high right now (about 1200rpm). The drop is sudden and 600 is only an approximation of when it stalls. This car has been an ongoing resto-mod project for me, and I have no problem replacing a 25 year old AFM as the next step. I'll let you know the results.

jondee86 wrote:What rpm does the engine normally idle at ?
How does the idle get down to 600 rpm ?
Does it suddenly drop from 800 or 900 rpm ?
Or does it slowly idle down until it gets to 600 rpm and then choke ?

There is a IDL switch inside the AFM that is held closed while the
air passing thru the AFM holds the flapper open. If the airflow gets
too low, the flap gets so close to being closed, that the switch open
circuits (removes a ground), the fuel pump stops and the engine
stops because it is not getting fuel

It could be that the AFM is shutting the engine down, but that does
not explain why your idle drops to 600 rpm.

Cheers... jondee86

Does it do it if you disconnect the ISC clip?
It could be sticking open then when it pops loose over corrects to the low side or something like that.

Nope. Does the opposite. Idle shoots up a few hundred rpm.

yoshimitsuspeed wrote:Does it do it if you disconnect the ISC clip?
It could be sticking open then when it pops loose over corrects to the low side or something like that.

Momosc wrote:Nope. Does the opposite. Idle shoots up a few hundred rpm.

yoshimitsuspeed wrote:Does it do it if you disconnect the ISC clip?
It could be sticking open then when it pops loose over corrects to the low side or something like that.

Try unplugging the ISC, adjust your hot idle to about 1000 RPM with it unhooked and drive it long enough to see if it's still doing the same thing.

Got the AFM out for refurbishment. See how she runs when it gets back. If I still have any issues, I'll try what you say, but what exactly am I looking for here?
Thanks, Mo

yoshimitsuspeed wrote:

Momosc wrote:Nope. Does the opposite. Idle shoots up a few hundred rpm.

yoshimitsuspeed wrote:Does it do it if you disconnect the ISC clip?
It could be sticking open then when it pops loose over corrects to the low side or something like that.

Try unplugging the ISC, adjust your hot idle to about 1000 RPM with it unhooked and drive it long enough to see if it's still doing the same thing.

OK, got the AFM back and the car still does the same thing. I'll try what you suggest. Again, what am I looking for here?
Thanks, Mo



Try unplugging the ISC, adjust your hot idle to about 1000 RPM with it unhooked and drive it long enough to see if it's still doing the same thing.[/quote][/quote]