Hesitation/bog problem advice

[Chicken_Lips]

I have had my nb8a for about a year now. Recently I noticed a hesitation and have been on a mighty quest to find a solution, which has been reinvigorated by a recent discovery.

Description:
From a cold start I have a hesitation, loss of power, in rev range 2000 - 4000 RPM. The car will sometimes lurch forward the power loss is so strong. Of note, it happens most intensely when the accelerator is depressed about 2cm-3cm and outside that range it doesn't seem to be as noticeable. Once warmed, the power loss is still there but muted, not as strong but noticeable now I am aware.

What I have done so far:
Air filter
Fuel filter
Throttlebody clean
Upper intake clean
AFR changed to new
Engine oil
Diff oil
Tranny oil
New sparks
New leads
Vacuum test (with carby cleaner, advised here)
TPS check - range .55V - 3.68V with no skipping voltages

So, now for what I did yesterday and the reason I am posting. I disconnected the TPS and my car transformed. I literally whooped in joy at the change. I have enjoyed this car for this last year but with that TPS dosconnected my mx5 became an absolute pleasure to drive. Torque, free revving power. I lost traction twice on the drive, simply because I had a completely different engine under the bonnet and didn't expect the change.

Before I was looking for an answer, now I must have an answer. I want that car, not this gimped car I have now!

[Magpie]

CAS Sensor?

Maybe worth a try, very cheap... cable tie to pull the plug in.

[93_Clubman]

Yeah, NB8As can have their issues - to give you an idea of what's going on:

In open loop for cold start & WOT (wide open throttle) or over 4.5k RPM.
In closed loop once operating temp reached up to 4.5k RPM.

Quoted from Miata.net:
"Closed loop = O2 sensor rules, tune should be near perfect
Open loop = All other sensors rule (O2 is ignored) tune tends to be rich.

If the TPS is not closed or wide open the ECU looks to the CAS & AFM to see if you're cruising.
If so, it goes into closed loop with the O2 sensor & ignores the others.
If you accelerate, it goes open loop & uses all the sensors to set the tune (rich).
When you close the throttle above 2K RPM fuel is cut altogether."

Manga also described it well:

An NA8 runs in closed loop mode when revs are below 4500 and you're just using light throttle. In closed loop mode the ECU uses the O2 sensor to help it set mixture.

It runs in open loop mode above 4500 or when you're giving it at least half throttle. In open loop mode the ECU only uses its internal fuel map to set mixture and the O2 sensor is not used.

[Chicken_Lips]

Thanks guys,

I've ordered a new CAS.

So, clubman do you suspect O2 sensor? I was considering an ECU + wideband once I had this issue sorted. Would the stock ECU be able to read a wideband if I upgraded it now?

[Steampunk]

Try simply cleaning the electrical connector for TPS and MAF (and other's you may think could do with a clean), perhaps it's giving weird signals due to poor/dirty contact.

http://www.jaycar.com.au/Service-Aids/Chemical-Aids/Aerosols/Electronic-Circuit-Board-Cleaner-Spray-Can/p/NA1008

http://www.jaycar.com.au/PRODUCTS/Service-Aids/Chemical-Aids/Aerosols/Deoxit-Gold-Contact-Cleaner-%26-Rejuvenator---Aerosol/p/NS1434

[hks_kansei]

Would the stock ECU be able to read a wideband if I upgraded it now?

Yes and no.

the standard ECU can only read narrowband sensors.

However, some Wideband sensors have the ability to also output a narrowband signal (ie: the gauge would read wideband and show the mixture, the ECU would read the narrowband and operate as normal)

[Magpie]

I've ordered a new CAS.

Did you try the cable tie test first? There maybe no problem with the CAS itself, hence no need to replace. The sign of a failing CAS is if it gets too hot and after it cools down car restarts without an issue. A 'dodgy' connection is a little harder to diagnose (I can give you the whole saga on it) however if it goes away and never comes back after using a cable tie then it is a connection not a sensor issue.

[93_Clubman]

So, clubman do you suspect O2 sensor?

At the moment O2 sensor wouldn't be at the top of my list. Know it might be frustrating, but the best approach with these issues is to troubleshoot the easiest & least costly things first, as per Magpie's & SP's posts, to which initially I'd add very carefully clean the MAF hotwire itself by spraying it with MAF cleaner.

[93_Clubman]

Issue with following NB8A sounds similar to yours:
viewtopic.php?f=29&t=66614&p=827967

[Chicken_Lips]

Thanks guys, this is my first car that I've actually done work myself. I've been a computer nerd for years and the way I do things is isolate amd replace. I'll try these things when I get back from my weekend away.

Issue with following NB8A sounds similar to yours:
viewtopic.php?f=29&t=66614&p=827967

It's a pity he never wrote back with the solution. The last step was the o2 sensor

[93_Clubman]

The last step was the o2 sensor

Yeah, I'd try unplugging it first as per one of the posts, but no harm in replacing O2 sensor, especially as if it's not been replaced since new, it's probably unserviceable anyway.
Usually an unserviceable O2 sensor simply results in richer running & therefore higher fuel consumption, but hks_kansei did find replacing his helped his NB8A which was not running on all cylinders.

Partially similar issue with this NB8A, also without posted resolution, but maybe try suggestion in last post of first page: viewtopic.php?f=29&t=29296

[Chicken_Lips]

Try simply cleaning the electrical connector for TPS and MAF (and other's you may think could do with a clean), perhaps it's giving weird signals due to poor/dirty contact.

I just finished cleaning every contact I could find. The stuff at the rear of the engine was particularly grimy. Just gotta wait for it to cool down now.

Yeah, I'd try unplugging it first as per one of the posts, but no harm in replacing O2 sensor, especially as if it's not been replaced since new, it's probably unserviceable anyway.
Usually an unserviceable O2 sensor simply results in richer running & therefore higher fuel consumption, but hks_kansei did find replacing his helped his NB8A which was not running on all cylinders.

Partially similar issue with this NB8A, also without posted resolution, but maybe try suggestion in last post of first page: viewtopic.php?f=29&t=29296

I disconnected the o2 sensor and the hesitation was still noticeable. The car also ran rough and lumpy. I'm not suspecting the o2 sensor so much after understanding the open/closed loop modes. If the problem is happening when the o2 sensor is ignored then it is unlikely that.

I'm not 100% sure where the IAC valve is. Is it just behind the throttle body in between the TB and the lower intake manifold? (With a vacuum hose running to the rear of the manifold)

[speed]

IAC is directly under the throttle body at the front.

[Chicken_Lips]

I haven't figured it out yet but I thought I'd give an update.

With all of the info here pointing to the intake area, I've ordered a gasket set. When I had the upper intake manifold off I got pretty keen to clean the rest out. I thought if I am gonna do this I'll do it right, so I'm gonna change all the gaskets and clean the crap out of the whole manifold.

With all of that out, what should I be cleaning? Is there anything only accessible with the manifold off I should refresh? Some radiator hoses maybe?

[Chicken_Lips]

Partially similar issue with this NB8A, also without posted resolution, but maybe try suggestion in last post of first page: viewtopic.php?f=29&t=29296

With the IAC disconnected the revs slowly drop and the car stalls