NA6 Air Valve & TPS

Gladiator · Postby **Gladiator** » Sun Sep 08, 2013 6:00 am

No I haven't replaced the CTS as yet but I did check it's continuity at cold & hot, & they seemed within specs I found on the other forum. I borrowed an AFM from someone to see if that made a difference but it didn't.

While I was trying to get to the neutral switch connectors, I discovered that I have an exhaust leak on my 4-2-1 headers, after the O2 sensor. Either where it becomes one pipe or possibly the flex joint. Would that cause my problems?

With the changes I've made to date, the cars behavior has changed a little. As of now on cold start it idles at about 1000 rpm (previously it would almost stall). As it warms up rpm increase to approx 1500 rpm. If I turn the fan & now non-existent A/C on the revs drop by approx 100 to 150 rpm.

93_Clubman · Postby **93_Clubman** » Sun Sep 08, 2013 11:35 am

Gladiator wrote:No I haven't replaced the CTS as yet but I did check it's continuity at cold & hot, & they seemed within specs I found on the other forum. I borrowed an AFM from someone to see if that made a difference but it didn't.
CTS usually fails causing the cold start issue where the car won't idle, or idles very poorly. But CTS can also become faulty, possibly intermittently, which can cause high idle. Reckon it would be worth trying to swap in a known good CTS if possible.

While I was trying to get to the neutral switch connectors, I discovered that I have an exhaust leak on my 4-2-1 headers, after the O2 sensor. Either where it becomes one pipe or possibly the flex joint. Would that cause my problems?
Wouldn't leave it, but wouldn't have thought it would cause the current problems.

With the changes I've made to date, the cars behavior has changed a little. As of now on cold start it idles at about 1000 rpm (previously it would almost stall). As it warms up rpm increase to approx 1500 rpm. If I turn the fan & now non-existent A/C on the revs drop by approx 100 to 150 rpm.
Wasn't aware there was also a cold start issue, but good that there's at least some improvement.

Gladiator · Postby **Gladiator** » Mon Sep 23, 2013 3:20 pm

I ordered a new CTS today so it should arrive in the next day or so. I'll post an update when I've put it in. I've been too busy to do anything since the last post. I haven't even booked it in to Automotive plus yet, I thought I'd try the CTS first.

93_Clubman · Postby **93_Clubman** » Tue Sep 24, 2013 10:56 am

Spanners crossed!

Gladiator · Postby **Gladiator** » Sat Sep 28, 2013 11:46 am

Well, I wasn't the CTS. I'm thinking it has to be electrical. Everything else has been checked or replaced. I might try and borrow someones ECU so I can rule that in or out as well. Other than that I need professional help I think.

93_Clubman · Postby **93_Clubman** » Sat Sep 28, 2013 12:33 pm

Yeah, worth borrowing an ECU if you can, or even pick-up one from John for $30: viewtopic.php?f=44&t=60034

Gladiator · Postby **Gladiator** » Sat Sep 28, 2013 5:57 pm

Is there any difference between Jap & Aus ECU for 1.6?

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gslender · Postby **gslender** » Sat Sep 28, 2013 6:01 pm

It could be the gasket between the idle air control valve and the throttle body. Every single TB I've inspected has had a worn and leaking gasket and this would easily raise the idle and/or make the idle valve difficult to manage the idle speed.

Worth checking at least if you are ok with removing the TB and associated coolant pipes around it.

G

mx5lover · Postby **mx5lover** » Sat Sep 28, 2013 9:10 pm

Similar to my idle problem,
happened after replace with long nose engine.
still not fixing it yet.
any possible Cause by the temp sensor at the back of engine?

Gladiator · Postby **Gladiator** » Sun Sep 29, 2013 6:36 am

gslender wrote:It could be the gasket between the idle air control valve and the throttle body. Every single TB I've inspected has had a worn and leaking gasket and this would easily raise the idle and/or make the idle valve difficult to manage the idle speed.

Worth checking at least if you are ok with removing the TB and associated coolant pipes around it.

G

Grant
I've already replaced the IAC & gasket, & like mx5lover, I've had this problem since I put in a long nose motor. Do you know if Jap & AUS ECU are the same?

93_Clubman · Postby **93_Clubman** » Sun Sep 29, 2013 12:01 pm

JDM & ADM ECUs aren't identical, although JDM & ADM specs were said to be 'similar' in Brian Long's MX5 book. Have noticed different components on ECU PCBs between JDM & ADM, & the JDM tune map is also likely to be slightly different due to 100 octane fuel. But don't know the exact net affect. From memory the JDM NA6 ECU also had a slightly higher rev fuel cutoff point. See Fatty's post in following about 'Myth Busted' - unfortunately the link in it to the Adaptronic MazdaMX5_Report no longer links, but will have a look to see if saved in the past - will post info if found: viewtopic.php?f=18&t=34732&p=449628&hilit=jdm+ecu+higher#p449628

93_Clubman · Postby **93_Clubman** » Sun Sep 29, 2013 5:06 pm

Full text of MazdaMX5_Report by Andrew Wyatt of Adaptronic formerly available from:
http://www.adaptronic.com.au/reports/Ma ... Report.php:
"Report on the NA Mazda MX5, 1.6L
The Test Vehicle
The test vehicle was an Australian delivered Mazda MX5, 1990 model. 98 Octane fuel was used.

The Background
Firstly, it is widely accepted that the Japanese version of the MX5 engine produced about 10kW more than the Australian version. The actual reasons behind this are often based on conjecture and assumption - for example it is well known that Japanese fuel was far superior to that available in Australia in 1990. Hence it is likely that the Japanese engine was "detuned" for Australian delivery. This may be in retarded ignition timing, or reduced compression, to compensate for the low octane rating of fuel at the time.

The Myth
The myth was that this detuning was all in the ECU. That is, one could get a Japanese-spec ECU from an MX5, plug it into an Australian-spec MX5, and immediately gain power.

This myth was easy to test, with an Australian MX5 and a Japanese ECU.

The dyno graph below shows the results (the highest peak power obtained from each configuration is shown): See dyno graph 1.

As well as testing Japanese vs Australian ECU, I thought I'd test the Japanese ECU with some more advanced ignition timing, to see if that made a difference to power output.

As can be seen from the graphs, the Japanese ECU consistently admitted more fuel to the engine, however there was clearly no extra power to speak of. Although this graph shows an extra 1 kW or so, there is really not that much in it.

We do notice that advancing the timing by 5 degrees makes a benefit to midrange torque, however no real difference to peak power production.

Test with Programmable ECU
The test was repeated using an Adaptronic ECU to control fuel and ignition timing. Both were tuned to achieve maximum power. No hardware changes were made to the engine, other than the addition of a MAP sensor, and in the green graph below, the removal of the airflow meter: See dyno graph 2.

As can be seen from the graph, the factory ECU is tuned quite conservatively at the upper end of the RPM range, and an increase of almost 10% at peak power is achievable without any mechanical changes to the engine or exhaust system. Furthermore, gains when compared to the stock ECU are clear right across the rev range."

Gladiator · Postby **Gladiator** » Mon Dec 15, 2014 8:20 am

YAHOO!! IDLE PROBLEM HAS BEEN SOLVED!!

Since I now have half a spare car, I swapped various parts one at a time. ECU, Air valve, then Throttle Body. That TB was the culprit.
Now idles at approx 1400 cold, dropping to 850 as it warms up. Hallelujah!!!

Rolley · Postby **Rolley** » Mon Dec 15, 2014 10:12 am

Finally!
Great news, I was starting to think it was just a combination of EVERYTHING being a little bit worn (including 20+ year old wire) and short of replacing it all you'd never get back to the baseline.
There's hope for us all!