AW11 SC MR2 dies when returning to idle

So my new to me MR2 don't like to idle when cold. No surprise there at it has huge cams. The main issue is that when coming to a stop the engine dies as it drops to idle out of gear. The previous owner put in a complete 2.5" intake system and thinks this might be causing the AFM to close fully and turn off the fuel pump causing the engine to die. Therefore I am thinking about seeing if I can somewhat easily add full time power to the pump. If his theory is correct, then it should idle as normal. Right?

I don't know enough about them yet but that theory sounds plausible but unlikely.

I think you have a "high idle" issue. Usually when coming back to idle, especially when rolling (often on the brakes, if power brakes using vacuum, and adding load to the alternator with brake light power draw) cars with carbs and early efi systems used a high idle setting that was like 1200 rpm or so. The engine would sit there to stabilize while still rolling and then go back to normal idle. Engines will usually pause at high idle even if not rolling as well.

Sounds like you are missing that. Does the vehicle speed sensor work? I think that is a big part of the high idle logic in older efi systems. There could also be some mechanical stuff at the throttle that does the high idle too - maybe look into andjustmente there?

I had a similar problem with my FX16, same 4age engine.  Replaced all the vacuum lines and now it runs, drives, and idles like a champ. 

AW11 is a 30 year old car.  Just replace all the vacuum lines.  Look for 3.5mm silicone vacuum line.  10 feet should do it.

It is highly UN-likely the 2.5" intake runners or fuel pump are causing your issue.

And for the AFM flapper to be closed, the motor would have to be off.  If the motor is running, even slowly, the flapper will be open enough for the pump relay to be kicked in.  Yeah, look for a vacuum leak, and there might be a high idle valve, like for the AC system.  When the AC compressor is on, it opens the little valve to let more air in, bypassing the throttle plate.

It has all new vacuum lines. Basically everything in the engine bay is new. That definitely doesn't rule out a vacuum leak. I will see if I can spot anything. 

I wonder if I turn on the A/C (which is present but doesn't cool) if that would help any. Certainly not a long term solution but I am curious to see if it helps at all. 

It will idle once it has come up to full temp. That takes probably 10 miles of driving though. 

Thanks gang. This is something that I haven't dealt with prior to this so it is good to hear that it might just be a vacuum leak. 

If vacuum lines are new, then it is most likely something else.  It could be the IACV (idle air control valve).  Look for coolant lines where the air goes into the intake manifold.  The part is NLA, but there is a someone who disassembled one for repair.  Might be gummed up and preventing the fast idle when cold.  It's basically a bi-metal choke valve.  

Hopefully it is something simpler, but I'm not sure what to recommend to check next.  The fact this happens when cold would lead to something monitoring temperature.

If I recall, there is no IACV on large port motors.  The cold higher idle is controlled by the throttle body.  That is, there's a coolant line that goes to the throttle body where "magic" stuff happens to let more air in when it is cold.  Even late 90's Toyotas did this.  Are there still coolant lines running to the throttle body?  It's a M4d y0 Tit3 mod to remove the coolant line to that so that the intake charge is cooler.

Looks like it is under the throttle body. Thought that nipple was it but I think that is a vacuum port.

I talked with the previous owner about this. This is what he has tried before.

"That was always a head scratcher for me.  I adjusted the tps sensor probably a dozen times, bleed the coolant so there were no bubbles in the iacv twice, did a smoke test for vacuum leaks, and wired in a dedicated power line to the fuel pump.  My gut is the pipe from the afm to the the throttle body it too large causing the arm to close when the throttle plate closes due to no enough air flow, possibly the bypass valve delete or even the NA throttle body although I wouldn't think that would be an issue. It's almost like it is not getting enough air and it chokes out.  I don't know how that is possible. "

Does it happen both when you are braking and when you are not braking? You could have a vacuum leak only in the brake booster which you would never be able to find with the car sitting still...

I have had a problem with that in the zx2. It ended up being the ac compresssor coming on and stalling the engine. Fix was more r134 but im sure thats not the only thing ill need to fix. Im leaning towards iac

In reply to Robbie :

It happens any time the rpms drop quickly, braking or not. Taking it out of gear and coasting kills it just as easily as braking to a stop in neutral.

In reply to ThatsNoUsername :

It definitely needs a recharge aad conversion. Not sure that it is coming on though. I don't have it on.

singleslammer said:

In reply to ThatsNoUsername :

It definitely needs a recharge aad conversion. Not sure that it is coming on though. I don't have it on.

Mine comes on with the vent and the compressor comes on during defrost on at least some cars to dry the air

So this is not the correct throttle body for the car, then, right?

Does it have a "throttle is closed now" switch?  Later Toyota EFI systems do, and I can't remember if that era did nor not.  Look at a schematic.  If it has one and it's not adjusted properly or not working, that could cause problems, I think even on a system without an IACV.

Time for a good old fashioned throttle stop screw?  I watched this car for months, and this issue kept me off it.  I'm looking forward to seeing the solution.

Dumb question but does it have a really, really light flywheel?  My M3 would do this when I installed a ltw flywheel...

In reply to docwyte :

Yeah, it probably has a light flywheel. I know that it is an aftermarket wheel. 

In reply to Dr. Hess :

No, it is an NA throttle body which is oddly bigger than the SC version. I have the stock one and will install it if some of these other ideas fail. 

I will check into the switches on the throttle. Maybe just throw a new one in. 

In reply to Tyler H :

Maybe, I would be happy forcing a 1500 rpm idle if that fixed this. 

This is the first modified forced induction car that I have owned. Is there a chance that the lack of a blow off valve (bypass valve) cause this? Throttle shuts, the SC has pressurized the intake track and doesn't allow the throttle to open enough to idle properly.

I dunno about the lack of a BOV.  Slamming the throttle closed would stall a turbo.  I could see it putting a heavier load on the supercharger as it is now trying to pump against a dead head, mostly, and that could add more load to the engine.  Kinda thin on the theory.

I had a Fidanza light weight flywheel on the 20v in my MR2.  No difference in idle at all.  Actually, zero downside.  I was part of the original group buy on that from Fidanza and they designed their flywheel to our specs/sample.