How to cure cold weather hesitation on the 2nd gen 3sgte - MR2 Owners Club Message Board
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post #1 of 71 (permalink) Old February 15th, 2008, 14:26 Thread Starter
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How to cure cold weather hesitation on the 2nd gen 3sgte

3S-GTE Cold Weather Hesitation:
One very common problem with the 2nd gen 3sgte is that its almost impossible to drive on a cold day, before it has had time to full warm up. The car might hesitate, buck, or surge, just when you are trying to drive it as slow as possible. Here is a simple fix that should cure the issue once and for all, and give you a smooth driving car, hot or cold.



The problem is caused by the AFM. Locate the AFM Idle Adjustment screw thats circled in red in the above photo. You should be able to see a big philips screw that you can adjust. If you have a metal cap over yours, you will need to carefully drill it out to access the screw. Now that you have access to the screw, here is how to adjust it.

1. Use a sharpie or a marker to mark the current position of the screw. This is very important in case you ever want to put your screw back to its factory position.
2. Give the screw 2-3 full COUNTER clockwise turns.
3. Reset the ecu by pulling out the EFI fuse, or disconnecting the battery for a few min. Do not skip this part. Its very important.

Now go take the car for a drive and let the ecu relearn. It might take a few cold days before you can fully verify if the fix has worked for you. If you feel the problem has come back after a few days of driving, try 1-2 more turns. Just dont over due it, because that screw also has an effect on your idle and a small effect on the over all ignition timing of your motor.

You should notice a very drastic improvement in how the car drives when the engine is still cold. Once it has full warmed up, you'll probably also notice a nice boost in throttle response.

What happens when the engine hesitates and why does this fix it?
When your engine hesitates, its actually running VERY lean. For some reason setting the adjustment screw, so that the ecu sees a tiny bit of less air fixes the problem and lets the ecu maintain a correct a/f ratio during a cold drive.

Will this have a negative effect on my WOT a/f ratio?
No, it shouldn't. Turning the screw 2-3 times makes the ecu see about 0.3% less air flow. Since the afm flap is already open 100% after 12psi, the 0.3% wont make a difference.

Other notes...

1. Make sure you are not trying to boost a cold motor. This fix only applies to people who have issues driving slowly and normally on a cold day.
2. Remember how many counter clockwise turns you made. That way if you have any issues or regrets, you can always set it back to where it was.
3. If the problem also happens on a warm motor, make sure you are using ONLY OEM wires, cap and rotor along with NGK copper plugs and that they have been recently replaced. You can get a new oem set of ignition components from ebay or your local toyota dealer for about 100bucks.
4. If the problem happens on a warm motor, under boost, then what you are feeling is knock response. If this happens, take your foot off the gas ASAP and lower your boost. Dont assume that 1xPSI is ok to "run" on these motors. Lower the boost by 1-2 psi until the problem goes away, and consider installing the tvsv led mod to see when your car is pulling timing due to knock.


Refer to this thread to read feedback from other 3sgte owners that have tired this fix.
https://mr2oc.com/showthread.php?t=285098

Last edited by lagos; February 15th, 2008 at 14:43.
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post #2 of 71 (permalink) Old February 15th, 2008, 19:09
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Thanks. I will try this in spring.
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post #3 of 71 (permalink) Old February 15th, 2008, 19:54
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While you have the AFM out, it's also a good time to give it a cleaning.
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post #4 of 71 (permalink) Old February 15th, 2008, 20:09
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thanks!
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post #5 of 71 (permalink) Old February 18th, 2008, 10:33
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Ok, so I'm trying this mod out right now. My question is, how deep do I have to drill? I've arleady gone pretty deep, (about 1/2 inch in so far) and I'm worried that I may end up hitting the screw, or damaging something that doesn't need to be drilled. Here is a picture of my progress so far:



My questions:

1) Is this the right place to be drilling?
2) How deep do I have to drill?
3) How much space is there between the bottom of the "cap" and the top of the screw?


Thanks,
Tom
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post #6 of 71 (permalink) Old February 18th, 2008, 12:35
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What if ppl with EMS and VPC/GCC experience the same morning cold start ups?
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post #7 of 71 (permalink) Old February 21st, 2008, 17:59
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1: Yes...right place to be drilling
2: Keep drilling a little bit more....
3: There is enough room, so that if you just go slowly you will not hit the adjustment screw. I was worried about that too. Just go slow and steady and you will be ok. You're almost there!
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post #8 of 71 (permalink) Old February 25th, 2008, 18:07
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I did this mod also.

Great stuff.

Just don't forget to reset the ECU. Like a dummy I turned the screw 3 X ccw and drive off down the street thinking: "just my luck, doesn't work for me". Then it hits me. I pull the battery cable for a few minutes, hook it back up. After a few days, it is driving great all through the warm up period. I can see the AFR on my wideband no longer reading as lean as 16.5-17:1 when at very light throttle and still warming up the engine. It's right where it should be at mid 14's.

Thanks Lagos!
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post #9 of 71 (permalink) Old February 25th, 2008, 21:15 Thread Starter
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Quote:
Originally Posted by califcarm
I did this mod also.

Great stuff.

Just don't forget to reset the ECU. Like a dummy I turned the screw 3 X ccw and drive off down the street thinking: "just my luck, doesn't work for me". Then it hits me. I pull the battery cable for a few minutes, hook it back up. After a few days, it is driving great all through the warm up period. I can see the AFR on my wideband no longer reading as lean as 16.5-17:1 when at very light throttle and still warming up the engine. It's right where it should be at mid 14's.

Thanks Lagos!
Glad it worked for you!
Its pretty amazing how smoothly these cars can run after this fix.
What air flow % are you seeing at warm idle on your safc after the fix?

Last edited by lagos; February 25th, 2008 at 21:27.
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post #10 of 71 (permalink) Old February 25th, 2008, 23:34
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hmmm, interesting stuff.
post #11 of 71 (permalink) Old February 26th, 2008, 00:31 Thread Starter
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I made a very simple video to illustrate exactly what happens to your a/f ratios on a cold morning when the car hesitates.
The video is not the best example because the weather that day was actually quite warm. Normally you would see the a/f ratio go even leaner, pegging the wideband into the 18:1 afr rage, and thats when the hesitation, bucking and surging would be most noticeable.

The second part of the video was shot today on a 30F morning while driving up a hill. You can see that the car provides the a/f ratio for the up hill load.

http://www.youtube.com/watch?v=3jxV9vN2dr0

Last edited by lagos; February 26th, 2008 at 01:48.
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post #12 of 71 (permalink) Old February 26th, 2008, 10:29
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Quote:
Originally Posted by tee
What if ppl with EMS and VPC/GCC experience the same morning cold start ups?

Take it back to your tuner, and slap him in the face.
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post #13 of 71 (permalink) Old February 26th, 2008, 10:33
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Quote:
Originally Posted by lagos
The problem is caused by the AFM. Locate the AFM Idle Adjustment screw thats circled in red in the above photo. You should be able to see a big philips screw that you can adjust. If you have a metal cap over yours, you will need to carefully drill it out to access the screw. Now that you have access to the screw, here is how to adjust it.
The "problem" is caused by the hot/cold map. ATS disables these when they do a ROM tune. It's an overprotective strategy by Toyota, to keep you from boosting on a cold engine.

Your "fix" reduces the airflow signal from the AFM, much like a SAFC. This modification will cause the same timing advance problem as reducing the airflow signal using an AFC.

I strongly recommend against performing this modification.

Ken
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post #14 of 71 (permalink) Old February 26th, 2008, 13:05 Thread Starter
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Quote:
Originally Posted by KBlake
The "problem" is caused by the hot/cold map. ATS disables these when they do a ROM tune. It's an overprotective strategy by Toyota, to keep you from boosting on a cold engine.

Your "fix" reduces the airflow signal from the AFM, much like a SAFC. This modification will cause the same timing advance problem as reducing the airflow signal using an AFC.

I strongly recommend against performing this modification.

Ken
Thanks for your advice ken, but I dont think your not 100% correct on this issue.

1. While I agree that there is a cold weather fuel map that is to blame for this issue, there is no possible way that these cars drove like this when they were brand new. I cant imagine someone just spending 20grand on their mr2 only to have it buck, surge, and hesitate on the first cold morning that they tried to drive it normally (we are not talking about boosting a cold motor). Something is happening that is causing the factory protection too come on WAY too early.

2. The problem has to either be caused by a worn out afm (possibly the air temp sensor) sending the wrong signal to the ecu or the afm reporting too much air flow once we remove our restrictive exhausts and intakes. I tried about 3-4 AFMs on my car, and they all had this problem, so I guess that can rule out the faulty afm theory.

3. Turning the screw counterclockwise will make the ecu see exactly 0.3% less air flow then before. There is no possible way that this can cause enough ignition advance to cause any form of problems to the motor. Im willing to bet that ATS adds a lot more timing advance then that to their ROM tune.

4. Its much safer to have the car run with the correct a/f ratio on a cold morning, with a tiny bit more timing advance, then it is to have it peg LEAN to a 17-18afr range every cold morning.

Last edited by lagos; February 26th, 2008 at 13:19.
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post #15 of 71 (permalink) Old February 26th, 2008, 13:24
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Quote:
Originally Posted by lagos
Thanks for your advice ken, but I dont think your not 100% correct on this issue.

1. While I agree that there is a cold weather fuel map that is to blame for this issue, there is no possible way that these cars drove like this when they were brand new. I cant imagine someone just spending 20grand on their mr2 only to have it buck, surge, and hesitate on the first cold morning that they tried to drive it normally
You're welcome. I've driven several very low mileage examples. (Deuce Coupe had 45k miles on it when I bought the car in 2/1999, and there is a local 93T that has 20k miles on it, as well as a 94T with 36k miles) They all exhibited this same behavior. I don't know if yours is worse than the usual, but every Gen 2 MR2 Turbo with a stock ECU that I have driven has exhibited bucking, surging and hesitation when the ambient temperature is below the threshold for the low/high temperature map. Disabling this map via ROM tune has cured the symptoms in every case. If your theory about the AFM being at fault was correct, then the cars would have continued to exhibit the poor drivability after the ROM tune. (Im not just referring to the ATS tune either, my 91T and 93T both were ROM tuned by G-Force Engineering, not ATS)

Best regards,

Ken
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post #16 of 71 (permalink) Old February 26th, 2008, 13:25
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Quote:
Originally Posted by lagos
3. Turning the screw counterclockwise will make the ecu see exactly 0.3% less air flow then before. There is no possible way that this can cause enough ignition advance to cause any form of problems to the motor. Im willing to bet that ATS adds a lot more timing advance then that to their ROM tune.
.3% across the board? You've measured this with an ohmmeter?
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post #17 of 71 (permalink) Old February 26th, 2008, 13:33 Thread Starter
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Quote:
Originally Posted by KBlake
.3% across the board? You've measured this with an ohmmeter?
Yes.
I monitored airflow % with an safc, which is essentially an ohmmeter. There is no significant impact on air flow readings by giving that screw 2-3 turns.

Its awesome that ATS and fix this with a rom tune. Thats a huge benefit for their customers, however this is a work around for people who do not have or plan on buying a rom tune.
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post #18 of 71 (permalink) Old February 26th, 2008, 13:53
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Mine does all of the above on my ROM tune. Warm mornings it does not.




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post #19 of 71 (permalink) Old February 26th, 2008, 13:56
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Quote:
Originally Posted by lagos
Yes.
I monitored airflow % with an safc, which is essentially an ohmmeter. There is no significant impact on air flow readings by giving that screw 2-3 turns.

Its awesome that ATS and fix this with a rom tune. Thats a huge benefit for their customers, however this is a work around for people who do not have or plan on buying a rom tune.

I would expect it to have an increased effect at higher flap deflection.
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post #20 of 71 (permalink) Old February 26th, 2008, 13:57
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However, my afm screw has been tampered with as the metal cap is no more. How much I have no clue.




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