Hi,
This has been an ongoing issue since I bought the car 2 weeks ago. Symptoms as follows starting up from cold:
First 5 seconds - Idles fine on a fast idle, about 1100rpm
Drops down to 500rpm ish and dies in a second or two
Can restart and will run if I hold it a 2k rpm or above. Between 1k and 2k it splutters and misfires and threatens to cut out.
Once warmed up (3 mins driving at 22degC ambient), it runs/idles like a dream.
Ive gone through most of the EFI components, cleaning and checking, there are no error codes except 26, because theres no evap canister relay/valve or associated plumbing fitted. Following has been checked:
Plugs (replaced)
Air filter
Thermostat
Timing set to 14 deg
Leads check out ok (resistance and sparking in the dark test)
Both coil’s primary and secondary resistances tested
AV removed cleaned temperature tested
ISC removed cleaned, solenoid tested 12ohm, shutter rotating freely against spring, no codes (how to test in operation…)
Coolant hoses to above blown clean
Air bypass screw channel cleaned and warm idle readjusted with diag link in.
Clutch switch working, picks up idle 200rpm
Reset throttle sensor/switch
AFM range of movement, 2200ohm on 5-7 (i think) at 22degC, missing pinouts (see other thread) for full test.
Im running out of ideas, suspecting air temp sensor although no codes reported, battery was a bit flat too, but that shouldnt make a difference?
Any suggestions gratefully accepted,
Thanks
Mark
Yes, once warmed up. Link pin removal makes no change to rpm so that good I guess. Pressing clutch in changes rpm by about 200.
Thinking maybe the water temp thermistor out of spec, although an open/closed circuit code (09?) was not generated.
Cheers
Mark
Well,
Last night I checked the AFM at the connector using the diagram that Geoff pointed me to. I got the following results:
Resistance between pins per diagram @ about 24C ambient in Ohms at various flap positions:
C-D: 2006 Regardless
C-F: 50 Open - 270 Closed
F-D: 1980 Open - 2250 Closed
E-G: 280 Regardless
I noticed the values quite jumpy (not linear) on C-F and F-D as the flap was progressively opened. I would think that this would give a jerky acceleration, but it doesnt. Maybe the pot under the cover needs a clean. For those of you without the diagram in from of you, EG is supposed to be across the thermistor, the value looks a bit low, its supposed to be around 2k Ohm or so? CD is the flap pot with the pickup either from the CF or FD side. Did I read that right? EG needs to have the same value as CD according to the manual, maybe I got the pin sets swapped, im no electrician!! Is the thermistor in the AFM a user serviceable/replacable item?
Also, I started on a fully charged battery, still getting 5 mins of rich running (burbling and cutting below 2krpm) have to hold the idle above 2k for 3-5 mins before running normally. So its not the battery (long shot but Im getting desparate). Wondering if maybe the ISC valve is not operating smoothly under load or the AV is sticking (although seemed ok under test). The solenoid is within spec and the shutter rotates freely, but theres no way to know for sure in operation. I was thinking of addining a diagnostic pointer to the end of the shaft! The coolant pipes to the AV and ISC do heat up quickly so its not a blockage. If I could get spares, I’d swap them out, but were at the end of the world here on the Cape Tip, so cleaning and checking is the best I can do.
Any ideas please guys, Im at the end of my tether here!!
Thanks
MArk
PS interestingly, I went for a test drive forgetting to reconnect the AFM, and the car went very sprightly although I detected a bit of pinking so took it easy. With the AFM re-connected it dips a bit on acceleration and runs slightly less ‘cleanly’ (all when warm, no change on the cold running issue)
Try using this for about 4 tanks full of petrol. I had the same problem as you and tried lots of the things you have tried. During the use of 3 or 4 tanks of petrol it stopped the idle fluctuation.
A mechanic told me later that it could have been dirty.gummed up injectors. If you shop around you should be able to get it with the extra on special offers. This photo is about 2 years old so the price is not current. I use it all the time and have never had in more trouble in two years of using it.
Hi Pollyana
Thanks, thats the first thing I did on getting the car, keeping the fuel tank contents low, so the strength of the mix was high enough to make an inpact on the carbon deposits. I used the Wynns product here, a 350ml tin for about R35 (about 2 quid at current exchange rates I think.) Theres a good injector refurbisher here as well, I used for another car which had clogged injectors, they do a postal service, but the cars off the road for a week or so
Im thinking though, that its not the issue, as after the 5 min warmup, its almost as if someone hits a switch and the engine runs sweetly! (like an AV, or ISC solenoid-shutter coming unstuck!) Clogged injectors would give you a constant lumpyness surely?
Went on a run with the local club yesterday. Got 45mpg over 250 miles! so I guess its not running rich (or Im driving like a granddad). Im still suspecting the AV or ISCV, even though they appeared to operate in ‘lab’ conditions, im not sure that one of them is sticking intermittently or incorrectly adjusted in the warmup phase.
Thinking of testing the AV by cracking it away from the manifold to allow additional air in, once the engine dies, to see if its stuck closed. Does that sound like a valid test? I know it will go lean if I allow too much air in but at least it should fast idle rather than stall. I see that the standard test requires a blanking gasket to eliminate the AV in hot running problems, but I need to do the opposite for the cold running problem.
Also need to do this ‘click’ test on the ISCV as although the solenoid resistence is ok at 12 ohm, maybe its not being activated and remains in its limp home mode opening setting…
Any comments?
Thanks
Mark
Sorry to bring this up again guys, but I still have this problem and its stopping me driving the car as m not keen on running the engine cold to 2,5k rpm for 5 mins every time I want to go for a drive. Getting desparate, so I reread this guide: http://www.miata.net/garage/isc.html Let me recap on where I am, focussing of the problem area so maybe someone can contribute something to help me…
1) From cold, engine starts and runs 5 seconds, idling up to about 1200rpm, then dies off to 0 without touching the throttle.
2) On restarting, engine wont run unless I hold rpms over 2200 or so, otherwise they drop to 0.
3) After 3-5 mins at 2500rpm, temp comes up to normal and I can back off the throttle to idle and all is well.
Relevant steps taken so far:
With warm engine, diagnostic connector in place, set the timing to 14 degress BTDC and the idle to 850rpm.
2) Cleaned the throttle body, ISC and AV.
Tested the AV in cold and hot conditions
Tested the ISC shutter movement (manually) and solenoid resistance.
Conditions and thoughts:
Now, with the diag connector in, the ECU and sensors dont come into play at idle, so I can ignore those. The ISC default shutter position is important though. It was seen to be about 20% open as indicated in the isc guide when inspected. The AV should be open as I checked when it was removed, in the cold condition. (although it may have jammed closed subsequently after a run).
What I dont know is, is it going lean or rich on the warmup. I dont have a CO tester but I guess I could pull the plugs say 1 minute into the warmup, or alternatively, crack open the AV letting air into the joint, and seeing if that increases or decreases the problem, additionally spraying combustible fluid into the AV/ISC feed air intake and seeing if that increases the idle. These are difficult to do when having to massage the throttle to keep the engine running at 2500rpm though.
Please let me know if my assumptions are incorrect in any way and where I could be looking next.
Thanks
Mark
To be honest i cant contribute from a technical stand point as you have already visited everything I would have done and more with my limited knowledge.
However, one think i picked up on was that mpg figure. In nearly 10 years ive never heard of a MX-5 which was able to get near that figure.
These cars are known to not be that efficient. Even if you drive at 56 constantly during the middle of the night during cold spring time, with eco contact tyres and no other traffic or junctions id be surprised if you cracked more the 42mpg. certianly you couldnt have accelerated in a healthy manner.
So either you measured it wrong or you could look at the fuel supply.
Now im waiting for the flood of people claiming great mpg - none of which ill believe.
'preciate the input anyway! My figures were probably out on the mpg, esp since I had to convert miles to km to ltres per 100km and back to mpg! Anyway getting back to the subject at hand, help, anybody please?!!
Thanks
MArk
Well, after suspecting a faulty fuel pressure regulator (cold idle improved with the regulator output clamped), the actual problem was a small air leak via a cracked pipe from the cam cover to the throttle body. I hadnt picked it up even pressurising the intake manifold, but the pros did, and after taping up the hose, problem is 99% better.
