Idle dip, be gone!

satanoperca · Postby **satanoperca** » Sat Jul 12, 2008 9:35 pm

Hi,

Went to my mechanic the other day who rang diagnostics on my MX5 NB8A which had been experiencing idle dip and crap mileage, no error codes but +.01V reading out of the 02 Sensor - should be around 05v. After reading about the problem I went and picked up a 4 wire 02 Sensor (generic) for $60 from MX5 Factory in Ringwood. The OEM 02 sensor was $360 but comes with the right plug.
Went back to my mechanics shop (Brunswick Garage) which belongs to a mate, crimped the old plug onto the new 02 sensor and installed it in the car. The wire colors of the OEM sensor and the generic sensor are not the same, check on miata.net for the correct wire sequence. Ran diagnostics again and correct voltage detected, it was working. Took it for a drive and finally no more idle dip.

Car ran smoother, revved freer, no idle dip and will have to see if mileage is better over the next few weeks.

Cheers

Benjamin

gobsmax · Postby **gobsmax** » Sun Jul 13, 2008 1:20 am

Hi Benjamin,

What were the symptoms?

I have a similar problem when I down shift (usually in the lower gear 3rd to 2nd) and there is a drop in revs, as low as 200rpm. It's never stalled, but comes pretty close.

I've also notice a drop in revs when in neutral and you tap the accelerator.

The 80K service (oil, plugs, air+oil filters) has just been completed, but no change.

Thanks,
Alan

MX5CHIC · Postby **MX5CHIC** » Sun Jul 13, 2008 10:45 am

I'm interested to see if your mileage improves, I have had the exact same problem but it has strangely dissapeared since changing my petrol from BP Premium to Shell Premium ???? go figure.

My mechanic told me that he often cleans O2 sensors by leaving them soaking in white vinegar for a few hours, he swears that it works 9 out of 10 times.
He used to work at Mercedes so his advice has always been sound.

I have been checking my mileage carefully, when my car had the idle problem I got 410km to a tank - combined city and highway 50/50.

With the change to shell premium ($1.82 litre) I have travelled 530km to a tank on the first measurement. It also caused the idling problem to dissapear. I gave thought to fuel contamination but I purchased the BP fuel at 2 different stations.

Any thoughts? :roll:

satanoperca · Postby **satanoperca** » Sun Jul 13, 2008 12:05 pm

The symptoms of my idle dip problem was when I pulled up at a set of lights and my idle would drop down to 400rpms and then come back to 850rpms. I had cleaned the throttle body and cleaned the gunk around the idle set screw in the past and reset the idle.

I generally put in 34lts of petrol everytime I fill up and in the past was getting about 380Km, that in the last few weeks had dropped down to 300Kms and less. The car had been idling a bit rough and not revving freely when going up the rev range. Overall power had reduced slightly.
The exhaust was bit oily black, it does not blow smoke and compression on all cylinders is excellent, however if you rev the engine or sit idling for a minute or two there was a strong smell of petrol.

I had also notice small surges when accelerating in first and second gear after about 2500rpms.

I had tried several types of petrol but made little difference.

For the cost of the 02 sensor, it was easier just to replace it than to try and clean it. Today I have also fitted new leads as I am unaware of how old the current ones were. Spark plugs were replaced several months ago with irridium plugs.

I will be able to determine the milage over the next few weeks as I do both city and highway driving.

Will be going for a drive today.

Cheers

Benjamin

Postby **Okibi** » Sun Jul 13, 2008 9:47 pm

Good news,

Do you know the part number of the O2 sensor you bought?

RG.net · Postby **RG.net** » Sun Jul 13, 2008 10:39 pm

Okibi wrote:Good news,

Do you know the part number of the O2 sensor you bought?

X2

TieNN89 · Postby **TieNN89** » Sun Jul 13, 2008 10:58 pm

MXHEVN wrote:
Okibi wrote:Good news,

Do you know the part number of the O2 sensor you bought?

X2

X3

mr_rotary · Postby **mr_rotary** » Mon Jul 14, 2008 12:36 am

I had the same problems with my NA6 and wish I had replaced the O2 sensor a lot sooner. What a difference it makes and quite easy to do!

http://www.boschautoparts.com/Resources/VehiclePartFinder/

Postby **Okibi** » Mon Jul 14, 2008 12:56 am

1999 MAZDA MIATA L4 1.8 GAS

Part Number Description
13551 Oxygen Sensor - OE Type After Catalyst Calif.; Check / Replace Interval: 100,000 Miles

13551 Oxygen Sensor - OE Type Before Catalyst exc. Calif.; Check / Replace Interval: 100,000 Miles

13857 Oxygen Sensor - OE Type After Catalyst exc. Calif.; Check / Replace Interval: 100,000 Miles

13863 Oxygen Sensor - OE Type Before Catalyst Calif.; Check / Replace Interval: 100,000 Miles

15733 Oxygen Sensor - Univ Type After Catalyst Calif.; Check / Replace Interval: 100,000 Miles

15733 Oxygen Sensor - Univ Type After Catalyst exc. Calif.; Check / Replace Interval: 100,000 Miles

15733 Oxygen Sensor - Univ Type Before Catalyst Calif.; Check / Replace Interval: 100,000 Miles