Quick question (I think…) - am planning to clean the ISC valve, and will need to take the throttle body off in order to remove the ISC valve. I have a new gasket for the ISC valve (as recommended in the workship manual), but should I also get a new gasket for the throttle body itself? Or should it be fine to re-use the old one as long as it’s not visibly damaged?
The old one should be ok to re-use as long as your careful.
M-m
I just took mine of yesterday to have a clean up…I’m waiting for the postman to bring me another as it was less a matter of inspecting it, as sweeping it up off the floor.
I’ve always found the old plastic/paper gasket to be stuck fast to the throttle body on removal, or that it comes off in pieces. If removing it, you need to use a razor blade (can’t you actually buy these anymore??), to avoid scratching the faces.
Totally agree - just spent at least 10 mins with a razor blade gently removing the old gasket from one I am cleaning up.
You will probably find that the gaskets from the auxilary bits are more likely to stay in one piece.
As I recall (and its going back a while) the throttle body gaskets come as a set; the ISC valve screws are both very tight, and very soft, so in retrospect, removal of this for cleaning is not something I would undertake again lightly (chewing up of the screw heads). The rubber gasket was deformed, so you may as well replace it if doing so. Last time I ordered a set, it took a Mazda parts guy quite a while to identify it, as it doesn’t have an obvious name.
Thanks for replies - sounds like I’m not really going to know until I open it up whether a new gasket’s required or not - wish I’d ordered one when I ordered the ISC gasket, P&P costs more than the part… I am starting to wonder if cleaning it is really such a good idea though, especially after what AT said about the screws etc.
Reason I was planning to clean it is I’m still having problems with low idle (but only for a minute or less after starting engine) so am gradually working my way through anything that could be the cause… It’s a odd because the idle only droops immediately after starting, then after revving it a bit it’s absolutely fine.
I’ve done a lot of research on this now, and there’s a ton of stuff that could affect the idle - makes sense that the way I could narrow down my search is to eliminate anything that would affect the idle it at all times, not just after startup. eg I’ve ruled out spark plugs/HT leads for this reason.
Have so far replaced air filter, checked for air leaks, re-connected the O2 sensor (error code check alerted me that it’s wire had melted thru!), cleaned throttle body - cleaning ISC valve seems logical next step, but if anyone reckons I can rule this out as the cause of the problem, then I’ll happily skip it!
It sound like the Air Valve and/or ISC valve to me. You can test them on the car:
When the engine is cold, bridge TEN and GND in the diagnostic box and then start the engine. If the revs start around 1500 and gradually decrease to 850 when warm, then they’re both ok. If not:
When the engine is warm, disconnect the jumper and let the engine idle (should be 850 revs) and disconnect the ISC valve connector (it’s a pig to get at!) and the engine revs should immediately rise to 1500 revs. If not, the ISC valve is stuffed. If it does, then it’s probably the Air Valve.
Many thanks for that info victormeldrew, will do these tests at weekend, sounds simple enough and definitely makes sense to do this before taking anything apart.
Alternatively, if you have an led rig to interrogate the diagnostics, you can check the ISC valve. Error code is 36.
There is no code for the idle air valve.
Just checked the fault codes with LED, none came up. Then removed the LED, started the engine with TEN and GND still connected, and it was no different to any usual start - idle too low, engine shaking about a bit, slight squeal from belts (presumably from belts anyway - tension definitely fine, only ever get this noise on startup before idle settles).
So it’s failed the first test, and the fact there’s no error code would point to the air valve being the problem (thanks rhino666 for the info about the air valve not having an error code - hadn’t realised this).
I will try the second test anyway (disconnecting ISC valve) at the weekend when I’ve more time and hopefully better weather - but looks like I can probably pinpoint this problem to the airvalve?
Oh, and to test the airvalve, it’s the freezing it then warming it up thing, right? Any tips on removing the airvalve - looks like I should be able to get it out without having to remove the entire throttle body?
May end up taking it to a mechanic, but want try everything I can to fix this myself first. I’m not necessarily saving money this way though, I’ve now bought 3 parts I didn’t need… O2 sensor (turned out the old one was just unplugged!), HT leads (decided this wasn’t the problem, although they’ll of course be useful for next service) & ISC valve gasket (now looks like the air valve is the culprit!). Anyway, if I can at least diagnose the problem as definitely being the airvalve, I will be very pleased.
When was the fuel filter changed last?
This is very similar to problems that I have been having.
Very poor cold starting and a massive idle droop just after start up, unfortunately I had adjusted the idle screw to compensate for an ongoing idle droop problem, this it seems was caused by the blocked filter reducing flow and pressure, replaced filter and readjusted the idle and things are back to almost normal. I just have to adjust the throttle butterfly to compensate for wear and hopefully happy days are here again.
If you have a/c you can check if the the ISCV is working but switching it on . if the engine is warm revs should rise to 1200 due to parasitic load if it’s working, and if you have Power steering ther should be a slight rise as you put lock on.
Hope this helps
‘Any tips on removing the airvalve - looks like I should be able to get it out without having to remove the entire throttle body?’
I assume you are talking about the idle air valve which is totally separate from the throttle body - it’s the ISC valve that is connected to the throttle body.
Very easy to remove - its bolted to the top righthand side of the inlet manifold. Carefully clamp the 2 coolant hoses and make sure you don’t crush the metal pipes inside. Then slide two hose clips away from hoses, undo 4 x 8mm? bolts, carefully twist to break seal on coolant pipes and remove. I did this job on my girlfriends Eunos a while back - the whole process of removing the IAV and refitting replacment took a less than 10 mins.
Found all the bits now, air valve at least looks very easy to get at - how on earth do you disconnect the ISC valve wiring connector though!!! Probably don’t need to do this part of the testing as no error codes came up, but I guess it’s worth making sure. Still trying various implements to get at it, not given up yet…
As for the fuel filter, this certainly hasn’t been changed in a while (and wasn’t really on my radar till now tbh) - if it turns out not to be the air valve, I’ll probably take it to a mechanic, will get the fuel filter changed then.
Finally figured out how to remove connector - it failed this test too - rev’s didn’t change, no clicking. I should probably mention there is a constant clicking coming from somewhere round there, but last time I visited Autolink they diagnosed this as just noisy injectors. Anyway, no new clicking occured, no change in revs.
So I’m concluding ISC valve definitely at least part of the problem. Haven’t done the freezing-then-warming-up test on the airvalve yet, mainly becaue I’m worried I might take it off and find its rubber gasket needs replacing, then not be able to drive the car at all.
As for no error code coming up for the ISC valve, can I infer anything from this? eg could this suggest it’s just a bit clogged up as opposed to being completely knackered? Might be time for a trip to a mechanic…
Do you have a multimeter? With the electrical plug off the ISC solenoid you should be able to measure the resistance of the coil. It’s not unknown for them to fail open-circuit. Can’t remember what the typical resistance should be, but something in the tens of ohms sounds likely whereas megohms is obviously borked.
I just checked mine and measured 12 ohms.
No multimeter, though might be able to borrow one - thanks for checking the correct resistance. No air-con either (as someone else suggested).
Anyway, looks like there definitely is some kind of problem with the ISC and possible airvalve too. I’ve still got water thermosensor and air intake thermosensor on my list of things to check, but no error codes coming up for these.
You won’t necessarily get an error code for the thermosensors if they are staying in range but reading incorrectly. If the temp is reading 15c but the actual temp is 25c the ECU won’t know that this is wrong so wil fuell incorrectly and will not throw a fault code.
You can either replace or test of the car with a multimeter, pan of water and a thermometer.
Hope this helps
Johnners
Just to report back on this, problem quite possibly sorted now - took it to a mechanic to get a new fuel filter and O2 sensor installed (would have done this myself ages ago, but I don’t have the right size spanner for the sensor, and no way of going under the car to get at the filter) and the difference is instantly noticeable. Don’t know what’s responsible for the change, the sensor or the new filter, but the car now feels much more powerful and responsive at low revs - really felt like I was driving home a faster car than I’d gone there in! Engine has started perfectly too so far, though time will tell if the occasional low-idle-immediately-after-startup problem is gone for good.
If not, I’m now armed with a multimeter, so will carry out some more tests on isc valve, water thermosensor etc. Also have new gaskets for isc valve, idle air valve and throttle body, so will take these apart if necessary.
Fingers crossed it’s fixed though - thanks for all the advice, and particularly to lrjohn for the fuel filter suggestion! I really hadn’t seen that mentioned anywhere else, or in the Grainger handbook where problems with the engine management system are discussed.