Mx5 MK1 1.8 - Idle problem

[rossyl]

Hi

Recently had the CAS O-Ring and Cam Cover gasket changed. Whilst doing that the garage reset the timing.

This was done by an MX5 Specialist garage.

The timing was previously very advanced, around 14. Also the Idle Adjuster Screw was turned up to maximum idle.

Spark plugs were changed.
Timing was reset to normal
Idle Adjuster Screw, adjusted idle to idle around 800-900rpm

But, the car then OCCASIONALLY started to randomly search at idle. Going to 1,200 RPM, then dropping to stalling.

This is intermittent, happens when the engine is hot or cold.

Drove for a few hours, including a few "Italian Time Up's"

But it's still happening. Any suggestions for a fix?

Thanks

[finishing touch]

Mine did that.

I changed the MAF sensor for a s/h one for a tenner (just to test) and it now runs so well I didn't bother with a new one.

Paul G

[rossyl]

I used an Mx5 Tech ECU Fault Code reader.

It showed no faults.

I think that's rules out anything the ECU would show a fault code for? So, number 8, rules out the MAF.



1

Ignition pulse

2

Ne signal

3

G signal

4

SGT signal (1.8L)

8

Airflow meter

9

Water thermistor

10

Intake air thermistor in airflow meter

12

Throttle position sensor

14

Atmospheric pressure sensor

15

Oxygen sensor (output too low)

16

EGR function sensor (1.8L)

17

Oxygen sensor (output not changing)

25

PRC solenoid valve (1.8L)

26

Solenoid valve (Evaporative canister purge)

27

EGR solenoid valve (vacuum)(1.8L)

28

EGR solenoid valve (vent)(1.8L)

34

34 Idle air control (1.8L)

36

Idle speed control valve

[finishing touch]

Sorry. Only trying to help. (shrug)


I did use an OBDII reader.

Code reader said:- code "P0172 Fuel rich Bank 1"


Paul G

[rossyl]

Thanks Paul. I appreciate the help.

Good that you also used a code reader. Strange yours didn't trigger Fault 8. But it did at least trigger a fault that directed you to the MAF.

With mine showing nothing, it makes it more of a question mark.

I am guessing mine may not be the same issue then.

No idea what it could be!

[anonymous-user]

A common mk1 problem is called Idle Droop, so maybe try this fix (it worked on a 1.6 I had a few years ago):

https://www.miata.net/garage/KnowYourCar/S7_Idle.h...

BTW 12 to 14 degrees is a common mod on a mk1, it makes the engine less peaky and gives more torque lower down. With the timing reset to normal it will give the power higher up so you'll have to rev it more and there will be a noticeable power "step" higher up the rev range.

My 1.8 has been set to around 12 degrees since I got it as I feel it makes it more driveable without needing the higher revs all the time, same with a 1.6 I had for a few years before.
If you Google "mx5 14 degree timing" you'll find info about it.

Edited by anonymous-user on Monday 20th May 09:07

[mrciarano]

Drive it in traffic and put the car in neutral when you're about to coast or stop - does it stay at 1200 consistently or hunt? If so might be a good idea to check the vacuum system. Had the exact same symptoms but more pronounced when in traffic/more idling.