mx5cartalk.com

http://www.miata.net/garage/isc.html

The link there should help, there is a valve on top of the inlet can't think of the name sounds like it's playing up
It's a air valve, little like a choke when the cars cold

i have the exact problem.. hope i get an answer soon

serious wrote:My na6 has a cold start problem.
rough idle and easy stall when it is cold.
So i have to warm it up for about 5 mins, then it runs absolutely fine, even high rev no hesitation or miss fire.
Done fair bit of search all seem point to the green coolant sensor at the back of the engine,
So i change it today but problem still remain.
will that be water temp sensor at the front control the fan? But seems not relevant.
Or other possibility?

Any input will be much appreciated.

Yeah, front sensor is for fan & two rear sensors are for ECU & temp gauge. It's usually the green larger of the two rear sensors that causes rough cold start running, but seems like it's something else in this instance.

i had the coolant sensor replaced, and it did help the idle a bit. required less time to warm the car up and wont stall.

not sure if you have the same problem, but when the car is not warmed, there seems to be no power and cant even make up
a small incline

K.Ho wrote:i had the coolant sensor replaced, and it did help the idle a bit. required less time to warm the car up and wont stall.

not sure if you have the same problem, but when the car is not warmed, there seems to be no power and cant even make up
a small incline

Anyone know for sure what this problem is ?

I'm just about to pick up an NA6 that has these same symptoms described to me .

I was also told that the culprit was diagnosed as the 02 sensor but the owner then went on to say it is a single wire sensor, could anyone confirm that the 02 is a single wire sensor on an NA6 ?

He went on to say that the car reved up on its own when pushed over 3000rpm until it warmed up then it ran fine.

I'm not hyjacking all these cars seem to have the same / similar problem

please help someone.

Cold rough idle problem is usally due to the green topped coolant temp sensor at the rear of the motor failing. This is the sensor the ECU gets it's info from on engine temp, hence the poor running when cold as the ECU thinks engine is warm.

Yeah, NA6 originally had a single wire O2 sensor.

Basho wrote:He went on to say that the car reved up on its own when pushed over 3000rpm until it warmed up then it ran fine.

Are you saying no throttle application was required over 3k RPM as revs increased automatically?

93_Clubman wrote:Cold rough idle problem is usally due to the green topped coolant temp sensor at the rear of the motor failing. This is the sensor the ECU gets it's info from on engine temp, hence the poor running when cold as the ECU thinks engine is warm.

Yeah, NA6 originally had a single wire O2 sensor.

Basho wrote:He went on to say that the car reved up on its own when pushed over 3000rpm until it warmed up then it ran fine.

Are you saying no throttle application was required over 3k RPM as revs increased automatically?

Thanks for the eply

My understanding is that there was some throttle application and when taken to 3000 the revs then increased to about 5000 on thier own, he also said there was a lack of power.

The car has 80000 genuine klms on it and it's services are up to date-with the 80k service due-.

OK - ECU reset by disconnecting battery & pumping brake pedal can help when revs are a little temperamental, but this sounds like it could be a combination of things. Possibles are ECU temp sensor & ISC problem - this is worth a look for latter:
http://www.miata.net/garage/isc.html

From memory some years ago, there was a very basic bypass kit, but can't remember how much it bypassed - will post info if found.

93_Clubman wrote:OK - ECU reset by disconnecting battery & pumping brake pedal can help when revs are a little temperamental, but this sounds like it could be a combination of things. Possibles are ECU temp sensor & ISC problem - this is worth a look for latter:
http://www.miata.net/garage/isc.html

From memory some years ago, there was a very basic bypass kit, but can't remember how much it bypassed - will post info if found.

Thanks for that I'm picking up the car tomorrow and won't be very happy if it runs like a hairy goat if you can find the bypass post it would be most appreciated.

It was actually a bypass kit that I'd seen on US ebay in 'cars' etc under 'miata', but I don't believe it will help with your problem. It was one of those many & varied kits that claim to make you more power, but doesn't, not that that's the point in your case. Not sure if it's still being sold but here are a few refs to it on other forums:
http://forum.miata.net/vb/showthread.php?t=51796

www.miataturbo.net/archive/index.php?t-17036.html

http://forum.miata.net/vb/showthread.php?t=368388