Agree with ICV.. dirty air filter lets dirt through.

Carburettor cleaner and a very gentle hand is best.

As far as electronic testing, you can buy a tester to read fault codes and plug into the OBD socket.. But if you have to ask, the learning process is likely to be long and expensive..

Try ICV first.. with great care.

Then also the MAF sensor (I assume it has a MAF sensor)

Edited by madf on 08/11/2011 at 09:51

Hi m_loades
My Jazz has an Electronic Throttle Control System (ETCS) and hence no Idle Air Control Valve (IACV) - but thanks for the suggestion.

Hi madf
I have changed the air filter - surprisingly dirty, but it made no difference to the idle rpm.

I am looking at code readers - Drapers do one for around £200 - ouch! But my local parts shop will do a read out for £10, so I can use that. But I want the engine set up software to do my own tuning. This is difficult to find.

I don’t seem to have a MAF (?) sensor, but there is a Manifold Absolute Pressure (MAP) sensor. When I adjusted the tappets I noted the inside of the inlet manifold was coated with what appeared to be old mineral sump oil - I think this Jazz has had oil with a mineral content. So it is very probable that the MAP sensor is coated with old oil. If the sensor is reading a low pressure then I assume the Engine Control Module (ECM) will reduce the fuel, and hence slow the idle. I’ll clean it tomorrow and see if it is the problem. Thanks for your help and suggestion, which is much appreciated.

Hi lkirk Bairn
Yes, I am using the higher octane fuel with the additives and giving it a work out regularly. I’m also using Redox for a while to clean the engine and injectors as it was standing for around 10 months on dealers forecourts.

Thanks chaps for your replies.

Edited by FirstHonda on 08/11/2011 at 20:10

Hi madf -

Too late, I brought a RAC OBD2 code reader for £80 from Argos - made in China, so I know it's good! But seeing what a bargain you got, I'll set up a Paypal account so I can buy from the internet in future. But thanks for the advice and link. Much appreciated.

The MAP sensor is nearly £400 from Honda, and around £130 from my parts shop!! So, yes, I will be cleaning this precious object with great care. If I need a new one I'll try to see what I can find on the net. Cotton buds are a great idea!

When I've cleaned the sensor I'll post on here with the results, as a low idle seems to be a common fault.

Many thanks for your advice.

Today I tried the following -

Cleaned the Manifold Air Pressure (MAP) valve
Checked the open/close function of the positive crankcase ventilation (PCV) valve
Checked the On Board Diagnostic Two (OBD2) codes - no faults

Cleaning the MAP did improve things but it still dropped eventually to around 450 rpm. I'll give it another clean tomorrow.

Thanks for the help

Edited by FirstHonda on 10/11/2011 at 17:53

Hi madf

The throttle position sensor/valve are something I've not yet tried. I'll check them out tomorrow - thanks for the link

You cannot adjust those as they are set by the ECU>

Hi elekie&a/c doctor

Yes - I checked and cleaned the throttle body and butterfly valve, it looks as new with no sign of wear or damage. Although I cleaned a lot of black stuff off and cleared the edges of the valve, it made no difference to the idle at all, but improved the very low revs characteristics noticeably.

Thanks for the suggestion though - much appreciated

A Honda dealer maybe able to make some adjustments to the ECU but he will not be able to reprogramme fuel and ignition.

If you were able to access the software and cables and get the necessary unlocking codes the likelyhood is you would make it worse. Even if it idled faster it may fail the MOT after your tinkering. Without gas analysing kit and years of training and experience this type of tuning is not for the DIY'er.

Add to that the link in the post above is really useful to a guy with a Honda Jazz with issues. They the fek do these idiots come on here posting adverts for tablets and phones etc in the USA.

Edited by thunderbird on 23/01/2013 at 13:40