Erratic Idle

[MiraOwner]

Hi Guys,

Can anyone help me on an erratic idle issue.. recently cleaned up the TB by spraying some cleaning solvent while running the engine (ABRO product made for the purpose) car starts up and moves to a higher RPM than usual and gradually slows down to a crappy idle, and i notice that the idle is erratic, at a Red light. one moment it gets better, next moment my teeth rattles , what the heck is wrong with her?

i tried to clean the TB coz the good old people at the service station has put the air filter flip-side after blowing compressed air to clean it up. inside of the Air Box was having a film of black dust due to poor filtration and improper positioning of the filter. car was idling a little rough earlier now its erratic and still bad..

Thanks in advance!

[GTAm]

Did you clean the MAF or Air Flow sensor as well? Could have got contaminated with the poor filtration.

Fuel pump pressure ok?

[MiraOwner]

didnt clean the MAF dont know where it is.. but there is an IAC valve i didn't clean that. makes sense to clean that but is it safe to clean? will it screw up if i spary the same solvent or some other stuff. whats the right way to do this.. any other thoughts are welcome!

[jdnet]

didnt clean the MAF dont know where it is.. but there is an IAC valve i didn't clean that. makes sense to clean that but is it safe to clean? will it screw up if i spary the same solvent or some other stuff. whats the right way to do this.. any other thoughts are welcome!

It's safe to clean the IAC. Use carb cleaner. Do not use carb cleaner or any strong solvents on the MAF. Contact cleaner would do.

Edited September 5, 2012 by jdnet

[MiraOwner]

Thanks JD, i was reading up on the erratic idle. can this be caused by compression issues or misfiring of the engine at low RPM? i'm seeing in some internet forums people discussing this possibility.

[jdnet]

well it can be a number of things. When were the plugs and wires changed last?

[MiraOwner]

Plugs were changed around 10,000 Kms ago, i took them out and cleaned them 2000Km's ago, they were not fouled (no unusual wear patterns). 1 of the ignition coils is different from the others (not the compatible part). (this was installed by the previous owner i guess) i observed that this "black-sheep" ignition coil is having an oxidized connection (the spring that sits on the spark plug)will this be contributing to the cause as well?

[jdnet]

a bad coil would be a cause for concern. I would start there if I were you. How bad is the oxidation? The booth may not be seating correctly and letting moisture in. Either way if it's not the correct part, you should swap it. Does the plug that's in the cylinder with the bad coil look any different from the others (in terms of color/wear and tear)? Also with the car running and running rough pull the coil out of that cylinder, if it runs fine then you found your problem.

[MiraOwner]

All plugs looked the same.. nothing different on the one with the different ignition coil. oxidization is not bad. but its not as clean as the other one's (comparing) i will start by cleaning the IAC valve first, and then change the Ignition Coil, i've done the "pulling the ignition plug on cylinder test" earlier, engine reacts to each plug so i guess all cylinders are getting the voltage only concern is whether the voltage is weak on the one with the different coil. i guess i have no choice but to change it with the right one and see.

[MiraOwner]

and BTW is there a place i can do a proper cylinder compression test without blowing a hole on my pocket?

[The Don]

I think bad compression is probably the least likely problem, at least until you eliminate all the other usual suspects. The most probably culprit here is the MAF.

Usually erratic idle in fuel injected cars are caused by the following, so eliminate them before you do anybody else. It might also help to do a diagnosis before you start as the ECU might already indicate the problem.

1. Faulty Idle control valve (ICV) and the first cause of action is to clean it and see if it makes a difference.

2. Faulty mass air flow sensor and again the first cause of action is to clean it

3. Throttle position sensor (less likely)

4. Throttle body (particularly if the butterfly valve is not closing properly)

5. Map sensor (the sensor that measures air pressure inside the throttle body)

Bad coils plugs or cylinders does not usually result in erratic idle (idle is too high, too low, does not settle properly or goes up and down erratically when you are sitting in traffic), but rather an engine knock which is there all the time and this is accompanied by a loss of power. But with erratic idle the car will perform normally under acceleration but behave strangely only when idling.

[terrabytetango]

+! for iffy MAF

[MiraOwner]

Thanks Don for the input, i will get my hands dirty once i get the time and let all of you know what the outcome is.

[The Don]

Thanks Don for the input, i will get my hands dirty once i get the time and let all of you know what the outcome is.

Be careful when you clean the MAF. As JDNet mentioned don't use solvents like carb cleaner.

[MiraOwner]

Hi Guys,

Just now popped the hood and did some cleaning of the IAC valve and did a few rounds of testing... this is what i found out...

-IAC valve has no effect in the idle! i observed this by removing the hose and letting the air pass freely without the IAC valve controlling it the engine has absolutely no effect ( i did this while the engine is running) and throttle bypass goes through the IAC and ends up in a box like thing which i'm guessing is a charcoal canister the other end of the outlet hose of the canister goes into the maze of things and i cannot figure out where it ends.

and one more thing. i even held my thumb on the air inlet to the canister which i presume should technically feed the engine with air. and the engine still strangely has no effect and idle is rough and does'nt change.

BTW there is no MAF or any other AIR related sensors in this car. that i found out by reading the manual. ok now the question is is the charcoal canister the culprit?

[MiraOwner]

This is the actual EFI schematics that i took from the manual. thanks for all your help in advance. i'm counting on you guys to help me sort this one out. as if i go to the maka baas garage they will start with the usual suspects like spark plugs fuel injectors etc. etc. which i have already checked up.

and i'm guessing what they mean by ISC is the IAC? am i right?

[MiraOwner]

Another interesting thing i found, there is a hose that goes straight to the engine from the Air Cleaner. what is that for can that be clogged up? i see that as the first line to leave from the main Air Cleaner line in the above diagram..

[kelum_wj]

Another interesting thing i found, there is a hose that goes straight to the engine from the Air Cleaner. what is that for can that be clogged up? i see that as the first line to leave from the main Air Cleaner line in the above diagram..

Could be a breather hose Does the engine rev as it used to or is there a hesitation? Also is it with A/C on or off?

[MiraOwner]

I've made a sheepish mistake! the hose that goes to the canister has no effect of course..! coz its the other end that has the effect. i removed the IAC completely from the system and the car revs up pretty high then.. looks like the IAC is bust! i will need to replace it.

[MiraOwner]

Hi Everyone,

Sorry for bumping this one up again... i called up a parts store in panchikawatta where they sell parts for my car. effin IAC is 15900Rs.. is it me or isn't it too steep for a simple magnetic coil or / step motor driven tiny device? this is ridiculous...

[The Don]

Hi Everyone,

Sorry for bumping this one up again... i called up a parts store in panchikawatta where they sell parts for my car. effin IAC is 15900Rs.. is it me or isn't it too steep for a simple magnetic coil or / step motor driven tiny device? this is ridiculous...

After I read your first post on your diagnosis that the idle control valve was at fault. And the method you used to diagnose it in the end is the standard method as well (the revs going up when the ICV is disconnected if the ICV is faulty) so well done.

Is that price for a brand new or used one? To be honest if its brand new 15900 does not sound too bad. I recently replaced mine which cost 7000 for a used one!

[MiraOwner]

Thanks Don,

That's the price of a brand new one.. looks like i will have to pay for it.. would you advice on buying a used part for this? was that a temporary measure for you or are you planning on keeping your car for long?

[The Don]

Thanks Don,

That's the price of a brand new one.. looks like i will have to pay for it.. would you advice on buying a used part for this? was that a temporary measure for you or are you planning on keeping your car for long?

For my car you can't really get brand news ones in SL (you will have to order from the agents and wait) as my car was built in 1993. If brought brand new it is about 20K so price was not the issue. I just had to get it working. I have since picked up 2 more used ones from Ebay for the future In my car and all other vehicles who used this ICV this tend to be an Achilles heal (they fail). This is the second time I replaced in my car. Last time it only cost me 4500 but this time I think I was taken for a ride.

[MiraOwner]

additional question on this.. the car does not die when i seal the throttle bypass valve (ICV removed) although it slows down pretty low, but does not die. does it mean that the engine is getting air from else where which it not suppose to ? technically the car to remain in operation it needs air to burn the fuel so does it indicate a vacuum leak (also) apart from the ICV issue? i disassembled the ICV and cleaned it inside out. looks pretty neat. i want to diagnose the entire range of things before i go changing stuff. so any more advice on the above question will help me nail it down.

[The Don]

additional question on this.. the car does not die when i seal the throttle bypass valve (ICV removed) although it slows down pretty low, but does not die. does it mean that the engine is getting air from else where which it not suppose to ? technically the car to remain in operation it needs air to burn the fuel so does it indicate a vacuum leak (also) apart from the ICV issue? i disassembled the ICV and cleaned it inside out. looks pretty neat. i want to diagnose the entire range of things before i go changing stuff. so any more advice on the above question will help me nail it down.

This is a little baffling as well. The problem is the implementation of the ICV is exactly the same in every vehicle. But I am still reasonably confident that the ICV is faulty because of the test you did (the rpm goes up as soon as you disconnect the existing ICV). I think even a trained technician will go about fixing this issue through a process of elimination (fix the obvious issues and move to the next). Now it would be handy if you could borrow an ICV to test but other than that it is a bit tricky. Maybe you can do a deal with the dealer to return it if you don't need it.

The other problem issue might be the throttle body......... but its easier to test the more obvious problems first.