Hi all.

I posted a couple of years ago about my wife's 2002 Polo, AZQ engine 1.2 3cyl 65bph.

It failed the MOT on emissions. We took it to an expert in Warrington who found the cat had disintegrated.

A year later, the MIL lamp came on, with catalyst below efficiency. It still passed the MOT that year, and again last year.

I think there's an issue with one injector that causes it to run rich at idle, but only at idle. The MOT centre ran the fast idle 1st, and the emissions were perfect - HC and CO on the floor. They then ran the slow idle, and you could see the HC and CO increasing slowly as it idled and blew rich out of the exhaust, but the test was over before it hit the fail limit, so they had to pass it.

If you use it for a long run, the MIL lamp goes out, so it's only idling and short runs that have this particular issue.

Last Friday, my wife was on the school run, and the oil light came on. Just orange, which signals oil getting low. The oil was close to minimum, so she topped it up with the correct quanity of the correct standard oil. This is one concern as it's not obviously leaking oil, which means it's burned quite a bit - but a lot less than is "normal" (1l/600 miles) for this engine. It's never burned oil before though.

When she then came to start it, it refused to idle. The RPM would drop from 750 to 500, then it would just stall.

I came home, assuming she'd overfilled it (she said she couldn't see the markings on the dip stick), or the filler cap wasn't on. Oil was perfect. Oil cap was screwed down tight.

I confirmed the poor running. When the revs dropped, it sounded quite "boomy", as though the exhaust was blowing slightly.

I put my code reader on it, saw there was a P0106 (MAP sensor range problem), and bought a new one (pattern part) off ebay. I couldn't spend a long time trawling the internet looking for symptoms etc, and had to order it there and then to get it on Monday.

Once I'd had a chance to look further, it turned out that the P0106 code isn't always caused by the MAP sensor, but "other things".

I've just driven to the post office (they couldn't get the box through the letter box on Monday), with the MAF disconnected, as this causes the car to run better than with it connected. I got home (having stalled the car a couple of times on the way), swapped it out, to have it no better than before (as I'd feared).

There were error codes before I swapped it, as I expected: MAP sensor reading low, and air temperature reading low (caused by the lack of sensor). I also had a pending P0303 (misfire on 3), but this was only pending. This is the first time I've seen this.

Specific Symptoms

The car's power level is not overly bad (with the MAP off). It's got no problem reaching 4/5K rpm. It's not a punchy engine (with me sitting in it anyway!), but can keep up with traffic.

There is no problem revving the car. It doesn't go dead after 2k or 3krpm. Above idle, it revs smoothly with no obvious judder or misfire.

Idle is very poor for the 1st 30 seconds - you've got to keep the revs up manually. After 30 seconds, there's a 25% chance of it stalling. If the engine revs settle at 750, it's happy. If not, they drop to 500, cycle up to 1000, and back down, and so on. Once it starts this, there's a fair chance of it stalling.

Smells quite petrolly, but has done for years, at idle.

MIL on with P0106 fault almost immediately. There's no sign (apart from the pending one) about a misfire on any cylinders.

(Worrying symptom). Immediately after it's started, for the 1st 60 seconds or so, if you take the revs up slowly, and then slide your foot off the throttle, the revs dip quickly, and there's a metallic clack (which TBH sounds like someone flailing a timing chain inside an aluminium biscuit tin). After 60 seconds, it doesn't do this.

Plugs are a little sooty, but not fouled or oily.

At this stage, my list of suspects are (ordered by expense and aggro :-) I can fix 1-3 myself with 2nd hand/pattern parts bought off ebay.

1) If I have a leaky injector causing overfuelling at idle, this has now gone south good & proper, and has now gone so far it can't idle any more.

2) Idle control valve issue. I've heard they could be an issue on this engine. Holding an idle above 750 with the throttle isn't an issue. It's just the car can't do it itself.

3) EGR. It's the metal body version, not the finned plastic. I've seen a thread somewhere where someone suggested sucking on the small pipe from the air intake to the EGR. If you can suck and blow, then the valve's not in great shape. Can I blank it off on this engine? Even if it's a piece of shaped baked-bean tin lid, replaced with a proper steel blanking plate £2 off ebay). One thread had someone having the timing chain replaced, followed 400 miles later by exactly these symptoms. They reset the EGR, and that fixed the issue. Why would the EGR have lost its settings now though? I don't have the necessary software for this. I think you need VAG COM (Rosstech?) for this level.

4) I've got an air leak somewhere causing all the readings to be thrown out (in the past this has not shown to be an issue, as our friendly local mechanic went over it with a can of easy start, checking for leaks).

5) My real fear 1: Stretched and/or jumped timing chain. If the oil level was low, the hydraulic tensioner could have "failed", and the chain jumped a tooth. From what I've seen though, this isn't the typical "jumped timing chain" symptom, as the performance gets poor at high rpm. This may tally with the metallic clack noise. (Test: check timing alignment marks)

6) My real fear 2: Burned out valve. (Test: Compression test)

What do you think my next steps should be? The car's 12 years old, and I don't want to spend dead money on it. It's a bit of a money pit already, having had various sensor failures, cat failure, door lock issues, coil packs failing, entire CAN bus controller burning out.

We're going on holiday on Thursday (in my car, thankfully!), so I'd like to get some idea of what I can do with the damn thing, even if it's take it to a local garage and say "Bad idle - check these things...". An option is a local chav, bung him a fiver for a gallon of petrol and a tenner for his trouble and a pack of matches (<JOKE - I'm not encouraging arson or anything. Just a little fantasy!)

Any advice or suggestions are welcome! Have I missed something?

Many thanks.

Pete.