Unstable idle with stalling as a result

I`ve had some strange idle problems before wich spontanously dissapeared, but they are back again !! .

The problem:

Car holds back at bumpy roads or completely random at the highway. Revs drop to 200rpm when driving slowly. Doesn`t respond at throttle, revs won`t go up or anything. Only a clunky noise appears from the exhaust downpipe. Today i parked my car with stable idle but when i closed the door the problem started occuring, so it seems that some kind of bumping the car triggers this.

Also i can head i sharp scratching noise wich seems like a slipping belt mostly heard when i`m stearing on very low speeds, i.e. when parking.

Ive changed spark plugs and refurb`d coilpack connectors to new one (where previous owner use regular connectors with some added glue to hold together !...)

If anyone has a good idea where i should look at to solve this problem i`ll be glad to hear from you.

You obviously have a loose connection somewhere or a bad earth from the battery. Check your battery terminals and clean them before re-connecting. Naturally, the battery might need a top up and it's quite possible that the alternator is faulty or worn out and the battery can't cope on it's own at low speed.

You can run one of these engines on a dead alternator for over an hour with headlamps on so switch off the engine, switch on the headlights and then switch on the engine again, watching for the headlights to brighten a little once the engine is running, indicating a working alternator, as it puts out a slightly higher voltage than the battery, so it can charge it, of course.

Failing the obvious connection checks, particularly for a bad ground to the chassis, without which the ECU can't work properly and if you think the battery and alternator are ok, you might want to check the diagnostic fault codes. It's a bit fiddly but might be worthwhile if you can't find anything obvious.

Here's a link that explains this procedure...

http://www.mkivsupra.net/vbb/showthread.php?35920-How-To-Check-the-diagnostics-codes&highlight=Fault+code

You might 'simply' have a BHG, (blown head gasket), as the symptoms are classic but it's not the most likely cause at this stage, given the intermittent nature of the fault. If you had a MkIII then it would be highly likely, as they were never factory torqued optimally.

However, if you have a badly sealing piston ring or valve, it can cause an intermittent loss of compression, so best get that checked. You can buy a cheap compression testing kit if you're a DIYer.

The scratching will be your power steering pump, (depending on the actual noise, which isn't clear), so you just need to check the fluid level, as a low level lets air into the system. If it's the accessory belt screeching, you just need to re-tension it. If the last change date isn't known and it looks fairly old, you're best replacing it. Same goes for the timing belt but they only break when they're not tensioned correctly and jump teeth or are so badly worn that they fray and snap. If there are no signs of wear, you're probably ok until the next major service.

Really dirty engine oil can also contribute to a poor idle, of course. As always, it helps if you can make a video. Saves all the guesswork and confusion.

I had some very fruity behaviour once because a lot of the pins on the plug that goes into the ECU weren't very tight. Moving the cables would see things like the throttle position sensor or the MAP sensor drop in and out of function. I refurbished all the connections and stopped that odd behaviour. I wrote it up here:

http://www.mkivsupra.net/vbb/showthread.php?35917-How-To-Refurbish-electrical-connectors

It's a fairly quick and easy check, although a dodgy earth is probably more likely.

-Ian

I think these are the most suspect ground points for you to have a look at, in order of likelihood:

ED - ECU and sensor ground

EC - Igniter/ignition ground

EB - EFI main relay ground

BI - Fuel pump ECU ground

ED and EC are both attached to the intake manifold area, so worth having a look down there for loose/missing bolts. I had the bolts holding EC in place work loose and fall out once, and the car didn't start at all.

I don't have access to my electrical manual at them moment (I'm at work on nights) so I can't post up the diagram showing exactly where these earth points are, hopefully someone else can

-Ian

its an mk4, no fault codes. used to have the common nr 42 but thats fixed now. Battery connections could be a good pointer..alternator does give 14.4V when running. On startup you hear a short sharp pitch, could this be due to a low level PAS fluid?

On startup you hear a short sharp pitch, could this be due to a low level PAS fluid?

Quite possibly, yes. Just check it.

Steering pumps make an awful metallic whine when they wear out or run low on fluid.

If it's a squeal or chirp, then your accessory drive belt is worn or loose.

replaced battery and refurbed earth connection at the battery. Problem not solved. It even occured last time on the highway doing 120km/u on cruise control but it needed to struggle so bad that i was making 0.1bar pressure to even keep at 120km/u. Refilled the PAS fluid but i think it`s coming from the accesory belt. Next time it occurs should i try to make a vid of the engine bay to see if some of you guru`s here can help me out?

Next time it occurs should i try to make a vid of the engine bay to see if some of you guru`s here can help me out?

As requested, yes please.

Has this been sorted? You probably checked already but mine had a really low idle the other day and found the cause was the small screw bar on the throttle under the bonnet for adjusting the idle had worked its way out and dissappeared. Replaced it with one from the na and sorted

I haven`t had a look there but that would make me think that the problem would always occur and not randomly? But still, never hurts to double check