'99 1.8 engine swap on NA 1.6 ecu - rough cold start - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-25-2014, 09:22 PM   #1
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Default '99 1.8 engine swap on NA 1.6 ecu - rough cold start

Hey guys, I hope this is in the right section :P.

I did the aforementioned engine swap a couple of months ago, using the 1.6 ecu and throttle body (with flyin miata adapter).
I just cant seem to fix the rough cold starts the car has.
Everytime I start with the engine cold I have to catch it with the gaspedal or it will almost stall out.
Than I have to manually keep the revs up (I have a video of this).

I've already replaced my ecu thermosensor on the back of the engine, there are no vacuum leaks and I installed a 1.6 fuel pressure regulator today which didn't help either.

I'm a bit low on ideas now and was hoping somone might chime in :P.

Video:



Thanks for looking!
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Old 01-25-2014, 09:47 PM   #2
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Did you do anything special with the AFM? Possible you broke the temp sensor lead?
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Old 01-25-2014, 10:01 PM   #3
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Thanks for your reply!

I didn't do anything to the afm and even tried another one from a different car which made no difference.
The temp sensor lead might be theculprit, I'll check tomorrow :P.
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Old 02-01-2014, 02:06 PM   #4
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We checked the temp sensor lead by measuring the resistance on ecu plug, it was ok.
I'm really out of ideas now, upgrading to a ms3x won't do any good if there's an underlying problem.

One thing that went through my mind is that the problem comes from the FM throttle body adapter.
The adapter blocks off the air channel that goes from the idle control valve to the air valve that is on the side of the 1.6 manifold.
Maybe the idle control valve can't provide the engine with enough air on a cold start.
I'm not sure if my thinking is correct though...
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Old 02-03-2014, 12:05 PM   #5
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Sounds like an IAC problem. Use the throttle stop to crack the throttle open a bit if you think FM's adapter is blocking the IAC channel.

Once you can get the car to start and "idle", with or without the IAC, take the FM adapters off, get an ECU, and put an NB throttle body on it. Much better solution.
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Old 02-03-2014, 03:22 PM   #6
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I'm kind of using my foot as an IAC valve, opening the throttle like in the video.
It's constantly misfiring and sounding like a v8 for about a minute, even with the throttle partly open.
Afther the minute of v8 sounds the car runs and drives fine, but fuel consumtion has gone up about 20 - 25% from the 1.6.
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Old 02-03-2014, 03:56 PM   #7
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Quote:
Originally Posted by Opgedronken View Post
I'm kind of using my foot as an IAC valve, opening the throttle like in the video.
It's constantly misfiring and sounding like a v8 for about a minute, even with the throttle partly open.
Afther the minute of v8 sounds the car runs and drives fine, but fuel consumtion has gone up about 20 - 25% from the 1.6.
Sounds like a V8 swap to me.
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Old 02-03-2014, 04:05 PM   #8
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Hmm, you may be right... Let me go check real quick :P.
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Old 02-20-2014, 05:45 PM   #9
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Quote:
Originally Posted by Opgedronken View Post
I'm kind of using my foot as an IAC valve, opening the throttle like in the video.
It's constantly misfiring and sounding like a v8 for about a minute, even with the throttle partly open.
Afther the minute of v8 sounds the car runs and drives fine, but fuel consumtion has gone up about 20 - 25% from the 1.6.
I'm having similar issues with my 90 Miata with a 96 motor. On a cold start it will initially only idle at 850 rpm like I set the hot idle. Then after a brief stable idle it wants to idle at 450 rpm sputter and miss. I hold the throttle part way open to get past the initial warm up and then the car runs like a top and pulls nicely when hot. I've put a different ISC on the car and no real changes to the way the car runs.
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Old 06-18-2014, 07:47 AM   #10
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It wasn't that bad with mine.
I've changed some things that made the car run better, but I can't test it anymore because it's summer now :P.
I did change my o2 sensor to a 4 wire heated one, because the normal sensor didn't heat in my stainless steel manifold.
That cured all other problems I was having.

I suspect the bad cold idle is because there is no more air valve on the side of the intake manifold.
One of the air passages of the idle control valve goes through this air valve, but the passage is completely blocked by the throttle body adapter.
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