Erratic idle on turbo mx5

[Novice1]

For some strange reason my car when decelerating seems to have a spack attack. By that I mean the revs drop down to 500 rpm and if you really give it some stick then decelerate it will sometimes stall.
There have been no changes made to my car recently. I took it back to the tuner, he increased the timing and I notice when you first turn the car on it idles around 1300-1500rpm.
The idle soon settles down to around 1000 rpm. As the car gets warm the stalling, low rpm problem becomes more noticeable. The car also does a lot of gurgling when you turn it off. I have booked it in to have any air removed from the cooling system next week. Not sure if this is contributing to the problem or not.
Turbo cars, BLAH! LOL
Any help appreciated.
Cheers Novice1

[93_Clubman]

I took it back to the tuner, he increased the timing ... The car also does a lot of gurgling when you turn it off.

Ron, if by gurgling when you turn off the ignition you mean the motor doesn't die straightaway, but instead runs on briefly, then timing is slightly too advanced.

[Novice1]

I took it back to the tuner, he increased the timing ... The car also does a lot of gurgling when you turn it off.

Ron, if by gurgling when you turn off the ignition you mean the motor doesn't die straightaway, but instead runs on briefly, then timing is slightly too advanced.

By gurgling I mean you can hear sounds from the cooling system radiator.

I am told its air in the cooling system.
Cheers Novice1

[ampz]

There are a few things you can do with the tune, but from the original post mentioning a tuner, the wise move would be to take him for a drive so he can view your concerns from a real life perspective.

With aftermarket ecu's there are over run settings which can adjust the rate of deceleration and to what revs it disengages (starts firing the injectors again). Tipically (OEM) and for emissions reasons, the injectors are fully shut (all fuel cut) in overrun and to pass emissions this needs to happen within 2 seconds of throttle shut. This is all good for an emissions (and fuel economy) stand point, but can have adverse effects when sudden drops (clutch in) cause a lean condition and the engine has a hard time adjusting.

What has worked for me is to run the lower rpm ranges with a percentage (1-3%) of fuel back in the system. With 'simpler' ecu's this may mean turning overrun off around 2krpm and using a lower than vacuum (around 17kpa) tuning row to drop a little fuel into the tuning map. This has 2 effects, there's a little fuel in the chamber and settles the idle cells earlier (keep the values around idle consistent) and keeps the cylinder chambers cool (racecars use nearly no overrun and is why you see flames shooting out, but that kills mufflers and cat converters in no time). Also adding in a degree or 2 of timing on the lower vacuum cells around idle will help with the dip, but may create oscilations in the idle if too agressive.

If it is a recent event and the car ran fine before, you probably have a vacuum leak. The most common places are any hoses near the IM as they are subject to the most abuse. MY pcv valve on the rocker cover took a dump soon after I started boosting and the idle was affected (as well as the dipstick, it continually blew out and hit the bonnet).

Hope this helps

[Novice1]

There are a few things you can do with the tune, but from the original post mentioning a tuner, the wise move would be to take him for a drive so he can view your concerns from a real life perspective.

With aftermarket ecu's there are over run settings which can adjust the rate of deceleration and to what revs it disengages (starts firing the injectors again). Tipically (OEM) and for emissions reasons, the injectors are fully shut (all fuel cut) in overrun and to pass emissions this needs to happen within 2 seconds of throttle shut. This is all good for an emissions (and fuel economy) stand point, but can have adverse effects when sudden drops (clutch in) cause a lean condition and the engine has a hard time adjusting.

What has worked for me is to run the lower rpm ranges with a percentage (1-3%) of fuel back in the system. With 'simpler' ecu's this may mean turning overrun off around 2krpm and using a lower than vacuum (around 17kpa) tuning row to drop a little fuel into the tuning map. This has 2 effects, there's a little fuel in the chamber and settles the idle cells earlier (keep the values around idle consistent) and keeps the cylinder chambers cool (racecars use nearly no overrun and is why you see flames shooting out, but that kills mufflers and cat converters in no time). Also adding in a degree or 2 of timing on the lower vacuum cells around idle will help with the dip, but may create oscilations in the idle if too agressive.

If it is a recent event and the car ran fine before, you probably have a vacuum leak. The most common places are any hoses near the IM as they are subject to the most abuse. MY pcv valve on the rocker cover took a dump soon after I started boosting and the idle was affected (as well as the dipstick, it continually blew out and hit the bonnet).

Hope this helps

I had the cooling system completely flushed and it made a tremendous difference. I tried to get the car to stall but couldn't duplicate what was the original problem.

The car did run fine before. There is a coolant hose near the turbo that as a slight kink in it which I shall try and fix. Getting the car back tomorrow.....flushing the cooling system seems to have effected the idle....when cold. I took it back to the guy who tuned my car to check the cars idle when hot and cold.

Cheers Novice1

[Novice1]

Car is back to its normal self. Flushing the coolant system without removing the thermostat resulted in it being jammed.
New thermostat and another reflush of cooling system, adjustment of idle and running like a terrorist.
Cheers Novice1

[devski]

Holy bump batman

[zossy1]

Why bump? You have issues too?

The idle control valve on the MX5 is a well-known issue in aftermarket ECU installations. Each ECU has its own "fix" for the various issues you come across. One of the most common fixes is to run the OEM ECU for idle control. However, this is not obligatory. Idle issues can be solved with some patience, research and brain power.

MT.net should be your first stop for info on how to stabilise idle. Suffice to say, the more electric load you pull at idle, and the more accessories you're running (eg. A/C, P/S, etc) then the harder it's going to be for you.

[Hjt]

I have a similar yet different issue. My car runs fine when first turned over and warms up. But after 30 mins or so when I pull up at lights etc to stop my car idled funny at approx. 1500 rpm or 2000rpm.

Running idle whilst warm is set at 1000rpm.

Anyone know how I can test it for basic problem solving?

My cars a stock SP

[zossy1]

I have a similar yet different issue. My car runs fine when first turned over and warms up. But after 30 mins or so when I pull up at lights etc to stop my car idled funny at approx. 1500 rpm or 2000rpm.

Running idle whilst warm is set at 1000rpm.

Anyone know how I can test it for basic problem solving?

My cars a stock SP

Stock ECU?

Could be any number of things, but i'd be checking the idle control valve first. Could also be a blocked vacuum hose somewhere...?

[Hjt]

yeah stock ecu/internals, aftermarket bov (turbosmart by-pass)

i'd be checking the idle control valve first

I'll have a look asap, not to knowledgable at turbo vehicles and would rather sort it prior to letting a $80 an hour person do it.