Strange Idle Issue

[89turbosupraman]

Last year before storing it for the winter, the car started having idle problems. AFRs drop below 10, car occassionally stalls and the engine sounds bogged. If I dont do anything the AFRs will wander as high as 17-18 and the cycle may repeat if it doesnt stall, several seconds later. RPM seems to stay around 550-600. If I blip the throttle the AFRs jump back to normal and I can keep it from stalling. This only occurs when the engine has reached normal operating temps.
The car drives fine and afr's are normal during cruising.
I tested the ISC per TSRM instructions and cleaned it and the check valve after checking over everything else I could think of. (checked plugs and gaps, replaced plug wires, checked timing, tested coils, TPS, and AFM per TSRM instructions.
I didnt really get a chance to test the car before the weather turned to crap last fall so it got parked.
I pulled it out this spring and hadn't had the problem return until last week.
It's now acting exactly the same as it did last fall.
Does anybody have an idea what to test at this point?

 

[thevork]

Sounds like you need to check for error codes first

Anyway I had thesame problem a few years back and it turned out to be a defective wiring harness. I replaced my engine harness and good to go.

But you are still far from doing that. check everything else first ;-)

 

[89turbosupraman]

Yea Sorry, I forgot to mention that. The check engine light does come on when afr's bottom out but there are no codes? We have checked repeatedly with a buddies scan tool with no luck. We started to think the CEL was due to the car about to stall (slightly lower than normal rpm)

 

[jdub]

A lot of scan tools are not compatible...do this:
http://www.cygnusx1.net/supra/TechTips/engine_error_codes.aspx

 

[89turbosupraman]

A lot of scan tools are not compatible...do this:
http://www.cygnusx1.net/supra/TechTips/engine_error_codes.aspx

Thanks for your input... It appears to be storing 31. I actually never had to jump E1 and Te1 due to the CEL NEVER appearing in my 11 years of ownership. I knew it was just a matter of when and not if.
It's strange that the scan tool didnt work as it is used frequently on other Mk3 Supras? The shop sees them regularly.

 

[jdub]

Code 31 is the AFM or it's circuit. Start by checking the connector to the AFM. Clear codes by pulling the EFI fuse for 30 sec and drive. Re-check codes to see if it is still present.

Did you happen to clean the AFM recently?

There are several different codes that will not illuminate the CEL when they occur.

I never trust a scan tool.

 

[89turbosupraman]

Code 31 is the AFM or it's circuit. Start by checking the connector to the AFM. Clear codes by pulling the EFI fuse for 30 sec and drive. Re-check codes to see if it is still present.

Did you happen to clean the AFM recently?

There are several different codes that will not illuminate the CEL when they occur.

I never trust a scan tool.

I am going to test the AFM again as it hasn't been tested since late last fall before the car got parked. It did check out ok then but at this point I need to be sure. I will also check the connector again.
I have never cleaned the AFM.
The AFM was out and tested in another mk3 2-3 months ago because that supra ran like crap after an NA to Turbo swap.
It made no difference in that car.

As of now I dont trust scan tools either.

 

[jdub]

It's good you didn't clean it...typically those that do end up buying a new set of electronics. The MAF cleaners sold in parts stores is a sure fire way to trash the mirror in the sensor.

While you're poking around there, check the accordion hose for cracks/leaks.

 

[thevork]

Also don't take tests or measurements of the afm for granted. even if they appear to be in spec as per tsrm it still can be faulty (although there is a much smaller probability when tests seem ok) so it's best to go swap it out for an AFM that is known to be working.

 

[89turbosupraman]

It's good you didn't clean it...typically those that do end up buying a new set of electronics. The MAF cleaners sold in parts stores is a sure fire way to trash the mirror in the sensor.

While you're poking around there, check the accordion hose for cracks/leaks.

I have heard/read the horror stories from those that do clean it. The accordian hose and all clamps were replaced last summer (new not used) but I will doublecheck those also.

 

[89turbosupraman]

Also don't take tests or measurements of the afm for granted. even if they appear to be in spec as per tsrm it still can be faulty (although there is a much smaller probability when tests seem ok) so it's best to go swap it out for an AFM that is known to be working.

I may be able to get my hands on one but it will be difficult at best. I suspect (or hope) the plug or wiring due to the idle problem healing itself for almost 6 months.