Strange Check Engine Light issue

alexbwang · Postby **alexbwang** » Fri Feb 07, 2014 10:55 pm

Hi guys, the CEL turned on in the morning today and stayed fully illuminated (no blinking, just stayed on) for the entire duration of the 700+ km drive from Melbourne to Batemans Bay. Apart from that, nothing really out of the ordinary: fuel consumption normal, engine revs fine, idles fine, running a little rich occasionally.

The past couple of weeks the engine would sound sluggish on cold cranking (ie. take a few extra turns to get started) - I assumed the upcoming 100k major would resolve this.

I purchased the car about a month ago, since then I did a couple of engine oil changes myself and recently had all fluids / oils changed to synths, as well as the RWC without any issues.

Initially, my gut feeling is sensor going bad, but now I'm thinking perhaps it's a fuel quality issue... the reason I say this is because I've been mixing fuels lately: the most recent fill ups were of Liberty "100 premium" (I believe that's an ethanol mix), BP Ultimate 98, "Premium 95" from an independent country servo. I filled up on Shell V-Power tonight on an almost empty tank, after 5km drive I parked the car and upon restarting it the CEL went away.

Anybody experience this issue before? Any suggestions would be appreciated, cheers!

alexbwang · Postby **alexbwang** » Sat Feb 08, 2014 12:05 pm

Update: so CEL came on again this morning and remained on. Just arrived in Sydney and the engine started to pull fuel and behaving erratically under load (ie down shifting to accelerate or accelerating in 1st gear from the lights). Hopefully it will get to the Mania garage in one piece on Tue haha

speed freak · Postby **speed freak** » Sat Feb 08, 2014 5:28 pm

Have you had the code read to see what it is and why its throwing a CEL?

I wouldnt really drive it too much, too far or too hard until you have had the code read.

alexbwang · Postby **alexbwang** » Sat Feb 08, 2014 6:38 pm

speed freak wrote:Have you had the code read to see what it is and why its throwing a CEL?

I've got the car booked into Mx5 Mania on Tue so will get them to check ODB and repair.

It's now idling rough and sputtering under load, drives like a Hyundai, exhaust note is horrendous, engine burning rich. I'm embarrassed to be driving around Sydney like this; luckily few people will recognise me.

speed freak · Postby **speed freak** » Sat Feb 08, 2014 7:52 pm

alexbwang wrote:
speed freak wrote:Have you had the code read to see what it is and why its throwing a CEL?

I've got the car booked into Mx5 Mania on Tue so will get them to check ODB and repair.

It's now idling rough and sputtering under load, drives like a Hyundai, exhaust note is horrendous, engine burning rich. I'm embarrassed to be driving around Sydney like this; luckily few people will recognise me.

Probably best to limit driving it as much as possible imo until its checked out.

Could be a faulty or dirty air flow meter, or dirty/old spark plugs, maybe even coils or spark plug leads. Could just be something simple but it could be doing all sorts of things to your tune.

alexbwang · Postby **alexbwang** » Sat Feb 08, 2014 8:23 pm

speed freak wrote:
alexbwang wrote:Could be a faulty or dirty air flow meter, or dirty/old spark plugs, maybe even coils or spark plug leads. Could just be something simple but it could be doing all sorts of things to your tune.

One thing I did notice a few weeks prior was that occasionally the engine would pop, bang and crackle under hard acceleration. Initially I thought it might be the inlet hose getting blown off the manifold but everything seemed ok upon visual inspection - everything's tight and there aren't any cracks that I can see. Earlier today it was idling rough until about 3,500 rpm when the engine would jerk into boost and rev normally after that (until the next gear change).

I've experienced a similar problem with my Mk6 Golf which idled roughly and ultimately it was diagnosed as a cylinder that had lost compression, with only 15,000 kms on the clock - needless to say I didn't keep that piece of junk for long!

Thanks for your suggestion - ill baby the car to the garage and let you know what the problem is once fixed, cheerios

project.r.racing · Postby **project.r.racing** » Sat Feb 08, 2014 8:27 pm

sounds like it is overfuelling at low rpm or light load. 75% sure your O2 sensor is on the way out.

alexbwang · Postby **alexbwang** » Sat Feb 08, 2014 10:41 pm

project.r.racing wrote:sounds like it is overfuelling at low rpm or light load. 75% sure your O2 sensor is on the way out.

The car idles all over the place, mainly it feels like it's about to stall (with the AC on it definitely stalls) - revs dip as low as 400rpm.

From what I gather it could be any combination of O2 sensor, Idle Control Valve, Exhaust Gas Recirculation Valve, Bad plugs - anyway, I'll find out soon.

Thanks for your advice!

22Silver · Postby **22Silver** » Sun Feb 09, 2014 12:57 am

alexbwang wrote:
project.r.racing wrote:sounds like it is overfuelling at low rpm or light load. 75% sure your O2 sensor is on the way out.

The car idles all over the place, mainly it feels like it's about to stall (with the AC on it definitely stalls) - revs dip as low as 400rpm.

From what I gather it could be any combination of O2 sensor, Idle Control Valve, Exhaust Gas Recirculation Valve, Bad plugs - anyway, I'll find out soon.

Thanks for your advice!

My car was stalling at lights for no reason (idle drop) and after extensive reading I discovered that a dirty throttle might be the cause. Cleaned it, issue went away. There's a little valve/hole that was dirty with light, pollution and road gunk that wass too fine to be filtered out.

higgimonster · Postby **higgimonster** » Sun Feb 09, 2014 7:09 am

You have a vacuum leak and a poor spark in one or more cylinders.

O2 sensor won't cause a stall. If it is throwing bad data the ecu will go into open loop and the car would run fine.

EGR stuck partially open would definetly cause the problems you describe. Although off idle you wouldn't notice.

Unless you have a code nothing anyone says will be valid.

Sent from my LG-VS980 using Tapatalk

alexbwang · Postby **alexbwang** » Sun Feb 09, 2014 7:26 am

higgimonster wrote:Unless you have a code nothing anyone says will be valid.

Say, is there any way to force the ECU to display the error code through the CEL? I know it can be done on OBD1 systems by shorting two pins, could the same be done with OBD2?

project.r.racing · Postby **project.r.racing** » Sun Feb 09, 2014 8:34 am

alexbwang wrote:
project.r.racing wrote:sounds like it is overfuelling at low rpm or light load. 75% sure your O2 sensor is on the way out.

The car idles all over the place, mainly it feels like it's about to stall (with the AC on it definitely stalls) - revs dip as low as 400rpm.

From what I gather it could be any combination of O2 sensor, Idle Control Valve, Exhaust Gas Recirculation Valve, Bad plugs - anyway, I'll find out soon.

Thanks for your advice!

with that new bit of info. yeah i'd been leaning towards vacuum leak or iac.

project.r.racing · Postby **project.r.racing** » Sun Feb 09, 2014 8:35 am

higgimonster wrote:Unless you have a code nothing anyone says will be valid.

Turn off the forums now. No point to them.

speed freak · Postby **speed freak** » Sun Feb 09, 2014 9:46 am

alexbwang wrote:
I've experienced a similar problem with my Mk6 Golf which idled roughly and ultimately it was diagnosed as a cylinder that had lost compression, with only 15,000 kms on the clock - needless to say I didn't keep that piece of junk for long!

Haha that there is one of many reasons why I very much dislike Euro cars and Chinese and Korean cars. JAP cars all the way!

How does it idle when its cold?

The struggling to idle could be the IAC valve. So under light throttle its very rough and pops and crackles etc but once over say 4000 rpm and on boost its ok? Is fuel consumption the same or worse? Also is it more of a misfire when its rough or just really sluggish and backfiring?