Decelleration Issue - NB8B

speed freak · Postby **speed freak** » Sun Jun 16, 2013 6:06 pm

Hey guys,

I have a 2001 NB8b mx5 so with the 6 speed box.

Im having an issue where say Im slowing down for a red light Ill be braking and using the gears to slow down as you do but when the revs get to about 1500-1700 rpm the car / engine starts to jerk back and forth until the clutch pedal is pushed in. Its quit violent it rocks you in your seat as well as the car. This doesnt happen 100 % of the time though, today coming home from work it was fine but 95% of the time it will do it.

Every other car Iv owned you could slow down in gear (second most of the time) and let the revs drop to almost idle rpm before I push the clutch in but its virtually impossible to do in the mx5 which doesnt seem normal. The 5% of the time when the car doesnt jerk back and forth you can do just that keep it in gear until almost idle rpm then stop. It does this in any gear too not just second can do it in 3rd and 4th too.

Any ideas?

Cheers
Rhys.

de Bounce · Postby **de Bounce** » Sun Jun 16, 2013 8:55 pm

Could be the Idle Air Controller / Idle Control Valve is sticking
Give the Throttle Body a clean along with the IAC / ICS and electrical connections.

Cooney · Postby **Cooney** » Sun Jun 16, 2013 10:40 pm

I have the same issue with the same model that I bought recently. I just assumed that it was close to stalling and jerking a bit because of it. Happens a fair bit when I'm reversing, probably because I'm almost stalling it crawling out of the driveway to avoid hitting anyone walking past.
If you find that it's to do with idle settings then let me know so I can look into mine.

Cheers

yoda7356 · Postby **yoda7356** » Mon Jun 17, 2013 1:06 pm

I had a very similar thing with my nb8b.
After removing and cleaning the EGR valve on the rear of the intake manifold
I don't have anymore trouble.
The car now seems to run smoother and no more jerking or stalling
on the first start of the day.
Hope this helps.

John.

Zcootz · Postby **Zcootz** » Mon Jun 17, 2013 1:23 pm

I know it's not the question you asked but why ate you using the gears to slow down? Brake pad changes are way cheaper than a clutch and possible worn synchros...

sailaholic · Postby **sailaholic** » Mon Jun 17, 2013 1:30 pm

He's in gear while using brakes or coasting is my read. You certainly wouldn't want to be in neutral.

Sent from my GT-I9100 using Tapatalk 2

speed freak · Postby **speed freak** » Mon Jun 17, 2013 5:51 pm

sailaholic wrote:He's in gear while using brakes or coasting is my read. You certainly wouldn't want to be in neutral.

Sent from my GT-I9100 using Tapatalk 2

Spot on! Im slowing using the brakes obviously but I dont shift into neutral if Im in a 60 zone Ill slow for a bit with the brakes then usually go from 4th into second around 30 to 20 kmh then clutch in and stop. IS that not normal?

Thanks to all the replys too. Iv had the throttle body cleaned very recently. How do I clean the IAC and the ICS valve, just use contact cleaner? Also is there a diagram I can look at that will show me the location of these 2 valves?

Thanks guys.

de Bounce · Postby **de Bounce** » Mon Jun 17, 2013 7:27 pm

speed freak wrote:Thanks to all the replys too. Iv had the throttle body cleaned very recently. How do I clean the IAC and the ICS valve, just use contact cleaner? Also is there a diagram I can look at that will show me the location of these 2 valves?

IAC/ICS are 2 names for the same valve (and there are others). On a NB8A or B it lives under the throttle body and has 2 small coolant hoses running to it plus an electrical plug.
Do a search on "cleaning the IAC miata" which should give you an idea of what to look for.

speed freak · Postby **speed freak** » Mon Jun 17, 2013 7:49 pm

de Bounce wrote:
speed freak wrote:Thanks to all the replys too. Iv had the throttle body cleaned very recently. How do I clean the IAC and the ICS valve, just use contact cleaner? Also is there a diagram I can look at that will show me the location of these 2 valves?
IAC/ICS are 2 names for the same valve (and there are others). On a NB8A or B it lives under the throttle body and has 2 small coolant hoses running to it plus an electrical plug.
Do a search on "cleaning the IAC miata" which should give you an idea of what to look for.

Sweet thank you. I was thinking the 2 names sounded very similar haha so it happens its the same thing. cheers.

Rhys

speed freak · Postby **speed freak** » Fri Jun 21, 2013 3:05 pm

Well I think Iv solved most of the problem. I cleaned the EGR valve, cleaned a few sensors/plugs with contact cleaner and cleaned the throttle body again. Took it for a test drive and it seemed alot smoother but when slowing in gear it jerked twice when it reached about 1500 rpm but not as much as before.

I found a writeup on miata.net about the IAC valve and cleaning it but that was on a NA6 and by the looks of it it had 2 coolant pipes and one bigger pipe for air. I can only see 2 pipes on mine and both look like coolant pipes so I didnt touch either of them. Hence why I just cleaned the throttle body again.

More worryingly though, which may be the cause of this problem, I found my intake manifold has ALOT of oil and grime/gunk on the inside. I done all this when the car was dead cold when I first opened up the TB there was a pool of oil sitting at the front. Since cleaning this has gone but the IM is still messy. I take it this is not a good thing, will this kill my engine over time and could this mean it hasnt had good quality oil or frequent oil changes for this too happen?

It blew alot of sh*t out of the exhaust on startup with sharp blips of the throttle with the cleaner inside.

Iv got pics of the intake manifold and throttle body BEFORE I cleaned them and took it for a drive. Im yet to get aftershots.

Any ideas?

speed freak · Postby **speed freak** » Fri Jun 21, 2013 4:19 pm

These 2 pictures are from after the throttle body and intake manifold had the TB cleaner put through it. As you can see its much cleaner but still right up the back is dirty and lots of gunk.

Can you use Subaru's upper engine cleaner in these engines?

aviper4u · Postby **aviper4u** » Sat Jun 22, 2013 1:14 pm

So what's the story after the clean?

FYI never tried "upper engine cleaner" though all the feedback i have heard is its a waste of time no real improvment OR even creates probs unless people feel a "placebo" effect.........

cheers and goodluck

93_Clubman · Postby **93_Clubman** » Sat Jun 22, 2013 1:21 pm

speed freak wrote:Can you use Subaru's upper engine cleaner in these engines?

Plenty of forumites have used it, however marty085 had a bad experience after using it: ttp://mx5cartalk.com/forum/viewtopic.ph ... 92#p652192

speed freak · Postby **speed freak** » Sat Jun 22, 2013 10:44 pm

link doesnt work.

What do you mean whats it like after I cleaned it?

I mentioned it still has the rough and jerkiness when slowing in gear at 1500 rpm.

I dont know how to clean the IAC valve on the nb8b...

Anyone have any suggestions as to why there would be so much oil in my intake manifold though as per the pictures? I realise they arent the best but I had to resize them. Still runs smooth etc prob better after the throttle body cleaner but that oil worries me and I still need to get that IAC valve cleaned if I can work out how. Found a writeup for a NA but its slightly different to the NB8b anyway not sure about the nb8a.

Upper engine cleaner works great in subarus I know for a truth but I though they would work in the mx too but I might give it a miss

speed freak · Postby **speed freak** » Sun Jun 23, 2013 11:04 am

The pic below is my IAC/ISC valve on MY nb8b.

It has the 2 small hoses which to me both look like they are coolant lines, definately the one on the right is, and it has the electrical plug/solenoid off to the right.

The cleaning artical I found had all these plus an air pipe at the front but this was for an NA6 so can anybody tell me how to clean mine on my nb8b please?

cheers
Rhys