Stumble when engine warm

93_Clubman · Postby **93_Clubman** » Thu Jul 07, 2011 11:51 am

Patty wrote:My NB8A recently developed a quirk where ~15-20mins into my trip the power would disappear, almost like I took my foot off the accelerator, and then come on and off and so on.

93_Clubman wrote:Slight chance it's even the beginning of an intermittent fuel pump (caused by pump itself or in-tank wiring connections)...

Oh no! Have a look at the following, which also applies to the NB8A, ref the possibility of there being an intermittent fuel pump related issue: viewtopic.php?f=55&t=46425

Patty · Postby **Patty** » Thu Jul 07, 2011 6:13 pm

Ooh I've been meaning to perform preventative maintenance on the fuel pump and filter too! I actually have the filter already :lol:

I'll check the pump, 93_Clubman. Might try to actually diagnose stuff first from here on in rather than blindly changing bits... :oops:

Patrick.

gslender · Postby **gslender** » Thu Jul 07, 2011 6:21 pm

Though, when a car is around 20 years old, probably worth replacing if your time is worth anything....

Patty · Postby **Patty** » Mon Jul 25, 2011 3:45 pm

Me again.

Its been happening less so I havent' had much chance to toy around with the problem. I never noticed it before but I was sitting in the carpark one evening waiting for my windows to clear up the fog. When I give it a little throttle, sometimes it will drop revs, splutter and stall. I can save it from completely stalling by giving it more throttle. It happens intermittently but at least I can re-produce this one every so often. I couldn't get it to do it when I made it home, just on a cold start, and not all the time.

Not even sure if it's related to the bucking I already have but can it be related to the TPS? I can't remember specifically but the bucking may have happened as I was coming on/off throttle and somehow upsetting the TPS :?:

I was also thinking about the coolant temp sensor but since my problem happens warm I'm thinking maybe not...

Postby **Okibi** » Mon Jul 25, 2011 5:59 pm

You need a member with an NB8A nearby to help with trying to suss out which component it is (or get Mania to do the same), you'd expect there to be an error code in the ECU.

The AFM could also be causing it to suddenly loose power, also check your intake runner and hose from the cam cover to the intake isn't letting any extra air in.

And from left field .. I had the inside on a K&N filter start to de-laminate, a bit of plastic broke off the inside of the filter cone and would get sucked up into the AFM mesh sometimes when under fast acceleration. Glad I found it pretty quickly. :lol:

93_Clubman · Postby **93_Clubman** » Mon Jul 25, 2011 6:14 pm

Not sure re TPS, but re coolant temp sensor, it depends which it was as there were 3 on NA6 (2 at rear of head & 1 at thermostat housing); & 2 on NA8 (1 at rear of head & 1 toward rear hotside of block); NB8A?
viewtopic.php?f=18&t=47933

Apparently the NB8A does have an EGR & cleaning it can fix cold idle dip (although sounds like yours has been blanked off):
http://www.mazda-speed.com/forum2/index ... 742.0.html

A new O2 sensor can fix hot idle dip.

The bottom 5 threads here for both the above:
search.php?keywords=idle+dip+nb8a&terms=all&author=&sc=1&sf=all&sr=posts&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

Patty · Postby **Patty** » Tue Jul 26, 2011 3:05 pm

Thanks guys, its always good to bounce thoughts off someone.

Okibi I could always take it to Mania, wouldn't be the first time

. I'm just interested in my car obviously and I want to tinker with it. Might sound weird but I'm kinda enjoying trying to figure this out. Will consider pulling codes.

93_Clubman I've actually cleaned out my EGR valve, before I realised it was blanked off. I have an aftermarket header which came with the car and I think I used that exact link as reference :mrgreen:

.

It's kinda hard trying to describe it but its not the typical idle dip. The reason why I thought TPS was because it happens when I apply a little throttle (very little), (when cold) and seems like she's going to stall. I thought it might be because I'm letting in a bit more air and something's not telling the injectors to open and causing it to want to stall. Again it's based on nothing, just trying to generate some discussion.

I still do have my idle dip when I come to a stop and the car is still cold, thats for another day...

Postby **Okibi** » Tue Jul 26, 2011 8:40 pm

Patty wrote:...Might sound weird but I'm kinda enjoying trying to figure this out. Will consider pulling codes....

Nothing weird about it, I just hate to see you throw money at a problem when knowing which exact part to replace will be cheaper and have you enjoying your car faster.

Patty · Postby **Patty** » Thu Jul 28, 2011 1:58 pm

Well I do like to enjoy my car...

I had a read of this thread and decided to try it out as a process of elimination. Found out that the TPS electrical connector had one if it's mounting slots broken off so this morning I disconnected it and opened the throttle gently. It seemed to rev fine. Then I put the connector back on and gently opened the throttle again and it hesitated. I tried to push the connector firm with my fingers with varying smooth revving and some hesitation.

At the moment I'm driving with it disconnected and it hunts a bit at idle and idle dips hard when I come to a stop. The more accessories I have running the bigger the dip, sometimes down to 400rpm and I swear it's worse when I brake harder. It otherwise idles at about 1 - 1.1k rpm and runs ok. Over the w/e I'll try to clean the connections and cable tie it down.

I'm actually surprised I can drive with it disconnected. How does the ECU know how to run the engine without it? Does it default to the O2 sensor or CTS?

93_Clubman · Postby **93_Clubman** » Fri Jul 29, 2011 6:38 pm

Patty wrote:I had a read of this thread and decided to try it out as a process of elimination. Found out that the TPS electrical connector had one if it's mounting slots broken off so this morning I disconnected it and opened the throttle gently. It seemed to rev fine. Then I put the connector back on and gently opened the throttle again and it hesitated. I tried to push the connector firm with my fingers with varying smooth revving and some hesitation.

At the moment I'm driving with it disconnected and it hunts a bit at idle and idle dips hard when I come to a stop. The more accessories I have running the bigger the dip, sometimes down to 400rpm and I swear it's worse when I brake harder. It otherwise idles at about 1 - 1.1k rpm and runs ok. Over the w/e I'll try to clean the connections and cable tie it down.

I'm actually surprised I can drive with it disconnected. How does the ECU know how to run the engine without it? Does it default to the O2 sensor or CTS?

Patrick, good to hear you've been able to find something tangible that's causing a problem. Your post reminded me of the response that OP got ref the dreaded hesitation problem with a modded MX5 SE. The response might give you a steer in terms of understanding your issue:
http://www.mx5cartalk.com/forum/viewtop ... 81&t=45055

Patty · Postby **Patty** » Sat Jul 30, 2011 6:16 pm

thanks 93clubman. appreciate all the bones uve been throwing me

bit more of an update. it idled super high ~1300-1400 in traffic on friday. tps unplugged. this morn i wound down the idle adjustment screw to about 900 but when it idle dipped it actually stalled so... lucky i took the screwdriver with me... played around until it was happy again. theres a point in driving when the engines almost at operating temp where the revs surge and dip and thats when it idle dips. maybe its got something to do with this open close loop thingy.

anyway the quicker the tps is connected the better.

sorry for the crap formatting. typed on my N900

93_Clubman · Postby **93_Clubman** » Sat Jul 30, 2011 7:41 pm

In open loop for cold start & WOT (wide open throttle) or approx 4k+ RPM.
In closed loop once operating temp reached up to approx 4k 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 closed loop with the O2 sensor and ignores the others.
If you accelerate, it goes open loop and uses all the sensors to set the tune (rich).
When you close the throttle above 2K RPM fuel is cut altogether."

So, with your TPS disconnected you're running in open loop only.

Patty · Postby **Patty** » Tue Aug 02, 2011 5:23 pm

Well I cleaned the contacts and cable tied the plug down but doesn't improve the situation. So it looks like I might be in for a new tps. But just so I can eliminate wiring or other electrical issues first does anyone have a spare TPS??