Iratic Idle Issue

[petemcr 10]

Hey guys, I know this has probably been done to death and I've used the search tool, from what I can guess it's a MAF issue, I have VAGCOM'd the car, as it's OBD1 all I'm getting Is an error with the MAF and the O2 sensor. I suspect the O2 sensor might be due to the MAF being incorrect, am I going down the right route. I've managed to get a MAF which is on its way but this is what I'm seeing at the moment.

 

 

I've so far cleaned the MAF, reset the ECU, cleaned the ISV with carb cleaner and used electrical contact cleaner on the MAF plug.

 

Anyone seen this before or got some ideas what might be causing, it was only doing it when the engine was up to temp

[vw rule 19]

To be honest the VAGCOM scanner / software is pretty reliable, when it detects any errors and brings up a fault code 9 times out of 10 like I say it's normally correct.

For some reason VW / Audi and a few other VAG vehicles tend to have problems with the MAF sensors, they don't seem to last as long as other manufacturers, from what I've seen on different sites / forums.

 

The Air Flow sensor (MAF) can sometimes cause the revs to surge up and down erratically,

it really depends what part of it is damaged or how it's burnt out.

A faulty lambda sensor usually cause the ECU to go into limp mode, and enrich the fuel mixture which is why the engine can feel lumpy and down on power slightly.

But like I say it really depends how the sensor has burnt out, as it can sometimes bring up a secondary error code which is on a similar circuit within ECU.

Also check your main air intake plastic hose from air filter box to throttle body, because if that's split it can sometimes bring up the MAF fault code.

 

I've recently replaced my Mass Air Pressure sensor (MAP) on my later type MK3 Polo, as that was surging from cold, and still once engine was up to temp, I connected up my diagnostic scanner and it showed the fault was my MAP sensor, so replaced it and it's been fine.

 

I know the MAF sensor is usually connected to the air filter box, where as the MAP sensor is fitted into the inlet manifold, but they have similar symptoms when they play up.

 

 

Si

[petemcr 10]

Cheers fella, well just to add to this, the new MAF came today. So I've replaced it and left the battery off for 15 minutes to clear any stored values, started it and sure enough it was still doing it.

 

So I took it up the road to the garage to let them listen and he had said thr same, to check for air leaks, so on the way back I gave it a quick tickle down the road... The idle had now settled, it's still sitting a little high but it's no longer showing any errors with the MAf or O2, it did show a code for 00533 - idle adaption I think it was, not scanned it since though

 

Go figure, need to take it for a long drive and see if she's still bucking and struggling.

 

Thanks again for the info though 😀

[robrado974 1]

I have the same problem at the moment. I removed the MAF and it altered the idle and stalled . So it’s working. The other problem that I’ve never had before is I had a sudden loss of power, I was only a half mile from home when it happened. I put my foot on the throttle and it spluttered and would not pick up, then it was fine again .

[vw rule 19]

Is your battery charging ok via the alternator as well, because Jim whose a member on this Forum has a slight surging idle which I think possibly was down to a weak battery and weak output from alternator, which can flag up strange fault codes when scanning the ECU due to erratic voltage.

Also check vacuum hoses around the throttle body, and idle control valve as again that can cause the engine to surge or have rough idle.

 

Si

[vw rule 19]

Also I think on the 16v and VR6 Corrado's there's a small recirculate valve to help control the emissions, it's on the back of the air filter box or near that area, it's got two vacuum hoses, one from the fuel vapor canister, and then the other goes to I think the throttle body or inlet manifold, again check those vacuum hoses because they can sometimes split, but not enough to bring up a fault code but enough to effect the idle / running.

 

Si

[petemcr 10]

That was the issue mine had not long ago, in low revs it sputtered like it was struggling, then suddenly surged and shot off, also stalled when the revs dropped a couple of times. it's funny the alternator being mentioned as I've suspected mine was on its last legs, the car has been stood for a fair amount of time and it's on my repair list, just the idle was taking priority as it was charging, I didn't know it could effect the idle.

 

Changing the MAF seems to have helped having taken it for a quick spin out, I've had a look and a fair few of the breather pipes look to be missing clips, I'll take a pic but I was sure they didn't have any on them originally.

[vw rule 19]

On my 16v Corrado about 10 years ago it had a rough idle problem, which after a couple of days developed into the engine cutting out, basically my idle control valve (ISV) was shot, I tried cleaning it out which helped only very slightly, so in the end I purchased a new one from VW Main Dealer when they were still available, along with a new coolant temp switch as my engine was flooding with fuel, and that sorted it for me.

But on yours from what you've said, and in your video on YouTube it appears to be surging at idle, when you've checked your vacuum hoses and if they're ok then it could be the throttle body is choked up, or slightly blocked where the bypass breather / vacuum hose to idle control valve goes.

Also a faulty idle control valve (ISV) can sometimes cause the idle speed to sit slightly above 1000RPM, they do get fairly choked up inside and the inner valve can be difficult to clean as you can't really take them apart, you can only try to clean them with carb cleaner or possibly brake cleaner as a last resort, but it's usually hit and miss or if it does work the fault will still return.

 

Si

[a_riot 0]

I was having a sudden high idle a few months ago, but it was steady not fluctuating like yours appears to be doing. No codes, nothing obviously wrong, so I pulled off the ISV and gave it a really good cleaning, as well as the throttle body. Seems to have solved my issue as its been fine for months since.

 

I think the VW MAFs are typically fine, don't need cleaning, and work for decades. It isn't that complicated a device and has no moving parts, so I never understand why techs always suspect it first. Perhaps other manufactures make ones that fail, but its rare I hear of a Corrado with a bad MAF unless the owner start to clean it all the time. It cleans itself with heat, which will burn off pretty much anything so I'd just leave it alone and look elsewhere. A bad O2 sensor won't do that since if it gets weird readings it goes into limp mode.

[petemcr 10]

I've had a look this morning to see if I can spot any air leaks and notice 3 pipes kissing any kind of clips. I don't think it has ever had these so I'm not sure if it needs then so if anyone could let me know.

 

First one is from the ISV to the inlet manifold, this is the one that comes off the silencer and goes to the top of the inlet just below the throttle body, that's just a normal pipe pushed on, all the others have clips on them to clamp them down.

 

The other two are on the pipe from the rocker cover to the inlet boot, seems like it it has a sensor on it from the boot side. also the small pipe from the fpr to the inlet was damaged bit I've already replaced that one.

 

Could anyone let me know if this is right or which I am missing, or even better if anyone has a pic.

 

I drove it last night to get it to temp, seemed a lot better, it's no longer hunting but the idle is still massively high, around 1500k or a little below, helps to stop it stalling but I know it's not right, it uses to sit around 800 or so previously.

 

Thanks everyone for the advice

[petemcr 10]

Sorry to rehash this but I've just noticed something while I was replacing the alternator.

 

I was going round trying to nip up the intake manifold bolts and noticed, the very far right bolt towards the battery has stripped out, I've taken it out and the bolt is fine so it looks like it's the lower inlet.

 

I just wanted to run it by everyone but I'm sure this is where my air leak is going to be coming from, the idle is better but it still sits high, am I right in thinking this will be causing it to idle high and also run rich?

 

I'm debating taking it off and either replacing it, or having the garage up the road run a new thread into it with a slightly bolt just to hold it tight for now until I can find a replacement

[SteveM 10]

Just had an idle issue problem with my Dad's Mk.3 Golf cab (2.0l AGG code engine)

We replaced the MAF as it threw up a fault code when scanned along with a lambda fault, even though the lambda was replaced recently. Both codes cleared after changing the MAF so that sorted that, and it drove better, but the idle was still erratic. In the end we traced it to a faulty plastic pipe for the brake servo, leaking where it meets the servo. Lots of scrap Mk.3's have the same issue so I cut the pipe back an inch, heated it up with a heat gun and pushed the right angle end back into the pipe. Idle is now sorted. Might be worth a look with Corrado's being of a similar vintage?

[1200 bandit 10]

Spray brake cleaner around the manifold if the engine revs go up you have found the air leak

Get a tap,die set and recut the thread in the head ,fit a new bolt you never know it may work

Tap and die set is always handy to have

[a_riot 0]

I just wanted to run it by everyone but I'm sure this is where my air leak is going to be coming from, the idle is better but it still sits high, am I right in thinking this will be causing it to idle high and also run rich?

 

The intake manifold is after the MAF, so would be unmetered air. Typically unmetered air causes the engine to run lean, not rich, since you've got more air than you need, without the fuel to match.

[petemcr 10]

The intake manifold is after the MAF, so would be unmetered air. Typically unmetered air causes the engine to run lean, not rich, since you've got more air than you need, without the fuel to match.

 

That’s what I thought, but I didn’t know if the ecu was detecting it running lean and tried to rich up the mixture.

 

But, she has improved, I took the lower intake off and sure enough the end bolt had stripped out, so I put a new thread in and replaced the bolt so it’s tight on now and also cleaned up the surface as there was old gasket residue on it, new gasket on and sealed it back up, alternator has also been replaced so I took her for a drive, she’s a lot better now, no cutting out, no miss fire round the 1k range, mpg is up from 16mpg to around 26mpg and doesn’t smell rich now, which is a lot better.

 

Just had one occasion where she bucked hard, mrs thought I was doing it on purpose and stared chuckling as I tried to get back driving

 

So a lot better, only thing now is high rpm, not like before just idles at 1k now, but sits at 700rpm on a cold start and rises as the engine heats up, going with the blue temp sensor at a guess