MX5 - Lost coolant, now idle drops/stalls when releasing throttle

Hexa-dB

Member
The other day a pipe snapped on my water pump inlet causing all my coolant to leak out. I pulled over pretty sharpish, as soon as the temp guage started moving up, and got driven home on a recovery truck.

The engine bay looks like coolant sprayed around a bit and it's been sat in the damp & cold for a few days. I replaced the broken bit yesterday and refilled with coolant but couldn't get it to start. It would turn over and almost catch but not quite. Tried a different battery & jump starting which didn't work. We did eventually get it going this morning after drying anything we could see with kitchen roll and then giving it a bit of throttle as it caught.

The alternator belt squeaked as it started so I think it was still a bit damp but otherwise, while revving it sounded ok. As soon as I came off the throttle though the idle dropped right down, almost to a stall, then hunted up & down for a couple of seconds before settling down.

I took it for a drive for half an hour or so, up & down dual carriageways mostly, and it still does it and did stall at pretty much every junction where I had to stop. It restarted each time, but sometimes needed a bit of throttle to get going. Apart from that, when driving along it feels fine, there's no smoke or anything, the heaters blow nice & hot, the temp guage stays dead centre.

Could it be related to dampness somewhere (alternator maybe)? I drove it for a while to try and dry it out but it's chucking it down and the roads were all pretty wet. Is there any way an air lock in the coolant could cause it? (seems unlikely)
 
Coolant temp sensor, the one on the back of the block should be a green sensor underneath your coil pack!
 
Hmmm. From what I've read shorting GND and TEN in the diagnostic port will cause it to idle without using any inputs from temp sensor or TPS.
I wonder if that would help diagnose it?

Hope it's not that because it looks like a swine to get at!!
 
Doh! Looks like it was just a massive air lock. Bled it for a while and it took in loads of water. Seems pretty much normal now.
 
Doh! Looks like it was just a massive air lock. Bled it for a while and it took in loads of water. Seems pretty much normal now.

I was gonna say this , you probably had a massive air lock and the sensor wasn't reading right , as it might be reading a bubble of air!
 
Spoke too soon. Idle problem fixed but it still struggles to start (needs a lot of throttle pumping until it catches and idles like a tractor for a few minutes - revs and drives fine then).

Decided to try a compression test to eliminate head gasket problems and one if the HT leads was stuck. Tried the usual twisting/pulling to free it and it snapped, leaving a broken plastic shaft firmly attached to the spark plug.

Right now I just want to scrap the heap of crap!!
 
FFS!!!!

brokenhtlead.jpg
 
Still can't get the broken bit of lead out. It's coming out tonight even if I have to smash the hell out of it with a hammer.

I last started it up on Saturday and (once it started) it was a bit rough for a minute then ok. Took it out for a run and it was absolutely fine. Tried starting again from cold and it was hard to start and ran like a dog. Also smoked a fair bit (white smoke) which I'm sure it didn't when I took it out earlier. I was going to do a compression test but the HT lead broke in there so I couldn't.

Something else interesting - I noticed the coolant had specks of copper in it the other day, apparently a sign that K-Seal has been used. Maybe it had a suspected head gasket failure before..

Preparing myself for a blown head gasket now - if that happens I'll be breaking it for parts.
 
Why? You can get a new engine for not too much moola. I got me a 1.8 NB with gearbox, PPF, Diff and loom for like £200 or something.

Also for the record, I HAD to start my MX with the throttle down to get it to catch or it wouldnt start. Still drove fine and shit but was low in one of the cylinders.
 
Looking on ebay I can see more mk 2.5 engines which look like a nightmare to put in a mk2 (different loom/fuelling/lighting). The mk2 ones seem to be about £400, then I'd need to get it fitted - I can't even get a broken HT lead out, I'd never cope with an engine swap :wack:

I suppose should wait and see what happens when I get the stuck lead out & do a compression test.

Also - I did the LED diagnostic thing last night and there are no error codes logged. I was hoping to see a coolant temp / o2 sensor fault logged or something. :(
 
Its really easy to swap the engine. It was a mk2.5 engine we fitted to our mk1. So included the VICS setup on the intake chamber. You wouldnt be changing fueling or lighting or even the loom dude :S you just swap the engine ..

Also how come you cant get the broken lead out? Get some pliers on it and pull the bugger out! :p It'll be tight but man up and do it. :)
 
Everytime I yanked it with pliers, the plastic just broke (see pic above)

I'm going to pick up some longer nosed pliers in a minute and try again. If it doesn't come out I'll try splitting the plastic so I can get at the connector. It's ridiculous - I was pulling it enough to rock the car. It's also ridiculous that it spins freely but won't come out.

By the way - Did I see on Nutz that you had a broken HT lead? A yellow one from Autolink? Mine were from there too.

I basing the mk2.5/mk2 differences on this thread:
Naturally Aspirated 1.8 Build - Forced Induction & N/A Power Mods - MX5Nutz Forum
But then again my old mx5 mk2 is now driving around with a mk2.5 engine in it so it can't be that much of a problem
 
Yeh man snap all the plastic crap and find some metal and go from there. It'll just be stuck had it happen a dozen times now, A couple of them were autolink ones and yes they fell apart on me.

Trust me. I had next to no engine swap know how prior to swapping my mk1 to a mk2.5.. it was easy. Bolts and plugs. It all works a treat bar the VICs not being plummed in because we blanked it off until we can get an RPM controller. However the only work needed done with getting an EGR blank plate fabbed up.

Its do-able man.
 
Got the broken ht lead out and felt quite chuffed until I did the compression test.
It used to be nearly dead-on 190psi on all cylinders. It now has 95 / 64 / 55 / 82
:(
Now deciding whether to break it, mend it or get a new engine.
 
Depends on what you want most? I mean going by your avatar.. it looks like a UK NB1? Hows the rot on it? My girlfriend has a Mk2.5 and it just failed its MOT due to rotton arms. The whole underside is a MESS and its a 2.5! If the shell isnt too clean with a duff engine it wont be worth selling like it is imo, unless u want rid.

If it were me personally, Id put another engine in as I know its relatively cheap and straight forward if you have the space / tools / help. Get someone over who has a bit of know how if you go down that route.

To repair it.. I dont know how much it'll cost man. When I did a compression test.. I went on ebay and bought an engine for £200. Drove south and put it in my clio, was in and working within a day :p We just did an all nighter on it, and neither of us had ever done a swap before haha :D
 
Hmmm I've got space (outdoors, not much good in dark/rain) but also have 2 kids and a full time job so not much spare time.

First priority I guess is to SORN it and get some tax refunded! And get a cheap runabout.
 
Hmmm I've got space (outdoors, not much good in dark/rain) but also have 2 kids and a full time job so not much spare time.

First priority I guess is to SORN it and get some tax refunded! And get a cheap runabout.

:/ sucks man.

2004 Mazda MX5 VT Sport 1.8 16v Engine 23'000 Miles! | eBay

MAZDA MX5 MK 2.5 ENGINE 1.8, 69,000 MILES ONLY GOOD | eBay

2004 mazda mx5 1800cc engine mk 2.5 vgc | eBay

MAZDA MX5 EUNOS (MK2.5 2001- 2005) 1.8 VVTi ENGINE ASSEMBLY - GREAT RUNNER | eBay

MAZDA MX5 1.8 MK2 COMPLETE ENGINE 1998-'01 CLEAN +SWEET RUNNER, 79K MILES | eBay

Your right though, almost double what I paid.. :(

Mazda MX5 Mk2.5- 1.8 VVT Engine 2001 - 2005.breaking. | eBay

Just some I found.
 
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