1.6 petrol - bad starting, huge flatspot, no error codes

[kevina4]

Hi, my '02 1.6 petrol B6, just under 100,000 miles, has become very hard to start from cold. I turn the key and it fires and then dies. Have to do this about 4 times before it starts, then it hunts around 500-1,500 RPM for a few seconds before going to a smooth idle. If I let it run for about 1 or 2 min and turn off it will start first turn of the key. Fully warmed start is also OK.

Then on the road, it (sometimes) does not want to run below 3,000 RPM, push the throttle and it just hesitates for 2/3 seconds, like you ran out of petrol. At other times it will rev a lot more freely, but still some small hesitations. Once I get to 3k it goes well and sounds 'on song'. TBH, I'm not sure is this is a flat spot or a misfire, I'm not really sure of the difference (but more on that later).

There is no check engine light and a scan shows no codes (but my scanner is a really cheap one, 20 quid job).

I had a good look around visually and can't find anything. I did see a possible loose vacuum line going into the MAF and replaced that but no difference.

Background

Car has a history of running badly when it gets hot. Backfires and smoke. Always OK after it cools down. I learned to avoid this by turning on the heating when stuck in traffic - that keeps the temp down. That said the temp never goes above half way, but maybe a problem with the gauge.

Anyway, 3 weeks ago I was on my way to the NCT (our MOT in Ireland) and was stuck in traffic but I did my heater trick and thought it will be OK and it was fine when I left it in. It failed on emissions, off the scale bad. Got in and CEL was on, managed to limp home. Did a scan and got a misfire on cyl 1 (0301 IIRC). Plug was badly fouled (see pic).

I replaced the plugs and have had the problems I describe ever since. It did pass the NCT and emissions were well within limits.

To me, it's like it's not getting fuel, but if that was the case, it would be worse, not better at high revs?

Thanks!

 

[kevina4]

Sorry, could not figure out the image, here's a link to it:

https://i.postimg.cc/Ssn1X7wf/plug.jpg

 

[pauldazzle]

Coolant temp sensor would be my 1st suspect followed the MAF sensor, & finally the camshaft position sensor. All of these can be at fault without throwing a fault code. Use genuine parts too as "buy cheap buy twice" is normal for VAG engine sensors.

 

[kevina4]

Thanks Paul for your suggestions, I will look into that.

Temp sensor a good call, as I said I never see it go more than half way.

Is there any quick checks I can make before just throwing parts and money at it? I'll of course have a look myself, but if you have any links handy I'd appreciate it!

 

[pauldazzle]

It's worth investing inVagcom/VCDS if you are intending to keep the car. Saved me a small fortune over the years with the many VAG cars that I've owned, & several members of this forum too. Coolant Temp Sensor has 2 seperate outputs i.e, one for the gauge & one for the ECU. It's a very common failure & often only one output fails. Can cause chaos if the ECU side fails. Failing Camshaft Position Sensor is often effected by engine temp. With VAGCOM/VCDS it's easy to see if all the Engine sensors are working correctly.

 

[kevina4]

Thanks again. I really don't know how long I'll have the car. Here in Ireland it's hard and expensive to insure cars over 15 years old, but I did go again in Dec so I guess I'll have it till then. My laptop only works off the mains so getting a battery, plus VCDS may work out expensive for 1 year.

Anyway, I'll see if any garage can do a scan. Or, maybe I can find some simple checks I can do with a multi-meter.

 

[RAF_S7]

Thanks again. I really don't know how long I'll have the car. Here in Ireland it's hard and expensive to insure cars over 15 years old, but I did go again in Dec so I guess I'll have it till then. My laptop only works off the mains so getting a battery, plus VCDS may work out expensive for 1 year.

Anyway, I'll see if any garage can do a scan. Or, maybe I can find some simple checks I can do with a multi-meter.

Have a look at the VCDS Map (tab, top of the page) You may find someone close to you who can help with getting a scan.

 

[Retroman]

My guess would be an ignition coil (s). They typical "play up" when hot (heat soak) and cause starting problems. Commonly they do not present themselves on a code reader apart from a generic misfire code. Sensors would normally throw some sort of code and wouldn't usually limit a problem to just one plug/cylinder. This would also account for a plug being fouled by incomplete combustion in that cylinder and high HC at an MOT test.

 

[kevina4]

Have a look at the VCDS Map (tab, top of the page) You may find someone close to you who can help with getting a scan.

Thanks. I had a look there seems to be no one near me.

 

[kevina4]

My guess would be an ignition coil (s). They typical "play up" when hot (heat soak) and cause starting problems. Commonly they do not present themselves on a code reader apart from a generic misfire code. Sensors would normally throw some sort of code and wouldn't usually limit a problem to just one plug/cylinder. This would also account for a plug being fouled by incomplete combustion in that cylinder and high HC at an MOT test.

That was actually replaced about 3 years ago with a new one. Could I be needing one so soon?

 

[Retroman]

That was actually replaced about 3 years ago with a new one. Could I be needing one so soon?

Does your car have a single "coil pack" with HT leads between the pack and the plugs or the more modern individual coil packs on top of each plug? I thought it was probably the latter? You would expect one to last more than 3-years but I do not know the background i.e. was a 2nd hand one or budget aftermarket one put in?

Again, backfiring ONLY when hot tends to make me suspect an ignition coil. If the coil fails to operate properly (when hot) you will have unburned fuel being pushed down the hot exhaust.

 

[kevina4]

Hi, it's the coil pack at the back of the engine, single unit with the 4 leads coming out. It was replaced by an indy garage that I trust in that they said it was a new unit so trust that. Not sure if OEM though. I took it to the garage with the backfiring issue so t never fixed it. I suspect they just threw common parts at it.

From all helpful replies here, is seems clear to me I need a VSDS scan since my scanner shows nothing wrong. I'll try to check out as many suggestions as I can without it though, if it's not too cold this weekend!!!

 

[kevina4]

Hi, just to update you all on this.

So, I decided to wait till the weekend to have a more detailed look. I researched some YT videos on how to check the parts suggested here without VCDS, I decided to start with the MAF sensor, simply because it's easy to get at. One video suggested a first step is to unplug it and see what difference it makes.

So, I tried that Friday morning before leaving for work. Amazingly, car started and drove fine, with CEL on! I then reconnected it in the evening, expecting the problem to return. I cleared the CEL and started the car, again it was fine, and has been since then.

I am pretty sure the connection was not loose so I don't think re-seating it did it. Another unlikely possibility is, I got petrol on the way into work on Friday at my usual garage. My previous fill was at a garage I don't normally use at around the time this problem started. But it's a popular brand of petrol so doubt that.

Anyway, thanks everyone for your help. I may be back soon