GTI MkV missing (misfire) at low speed and revs

Hello All,

I've got a problem with my GTI. The engine is missing (misfire) at low revs (from a start) and also missing when driving the car normally at say 20-70ks per hour. For example if I'm just cruising/driving along at 50km per hour and just feathering on the accelerator, if I give the accelerator pedal just a little more juice the car misses.

Just a note: if i drive it flat out, there is the initial hesitation (misfire) but the car does not misfire through the rev range.

The car was initially diagnosed with some emission problems, the charcoal filter and a turbo valve was replaced. This didn't fix it. It been into the authorised VW dealers three times now and because the car dos not record any errors codes on the diagnostics computer, as far as they are concerned. It doesn't exist nor have any answers. I think the are of being a mechanic is now lost.

Any suggestions on possible causes? Coils, plugs, injectors?

Many thanks

John

How many miles since last plug and or coil pack change?

I have/ had the exact same issue and I've replaced all the easy, obvious stuff recently. I'm pretty sure in my case that it's a failing in-tank low pressure fuel pump. I have an R32 pump on the way. I'll let you know if that fixes my issues. I might already have fixed it though. I replaced my spark plugs last night with NGK Laser Platinums gapped at .026 and that instantly smoothed out my idle and made my car run smoothly for the 5 miles or so I drove it. So, time will tell if the issue was plug-related, or if the issues will return and maybe be fixed with the replacement lpfp.

I'm basically a Stage 2+ K04 car, so the source of my symptoms may be different from yours. It'd help if you included your mods (if any), mileage, recent maintenance, etc. to make it easier for us to try to pinpoint your issue.

Hi All,

Few details on the car. No mods, stock standard, 98 Model, 72,000ks on the clock, was serviced in July and apparently had the spark plugs done then. Next service due at 75,000.

lagomatic said:

Hi All,

Few details on the car. No mods, stock standard, 98 Model, 72,000ks on the clock, was serviced in July and apparently had the spark plugs done then. Next service due at 75,000.

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The car is too young to have major carbon buildup, so that's probably not a factor. Might be an issue with the coil packs, but you'd need a VAGCOM cable to know for sure, or you can replace them as preventative maintenance and see if that helps.

It could be a plug issue. I doubt they're worn out if you got them done at the dealership recently, but I'd check to make sure they are gapped correctly and consistently across all plugs. There's a good chance the dealership tossed them in right out of the box, and some of your gaps could be way off. That might be what's causing your car to miss.

You might also have moisture in your tank. Can't hurt to try a bottle of HEET Marine formula in your tank to help get rid of any excess water that can cause drivability issues.

Thanks for the tips, will try the HEET Marine formula. Dealership hasn't been overly helpful, hence why I'm here, anything involving "thought" and not the computer has got them stumped. I am covered by an extended warrantee so the car is covered. Just wondering if its anything a little more expensive than the norm and they are holding off doing the work.

Considering I'm about to buy another car, they've just lost my business and the next 5 years servicing. I'm sure the sales department will love them when I tell them that.

Bunnspeed said:

The car is too young to have major carbon buildup, so that's probably not a factor. Might be an issue with the coil packs, but you'd need a VAGCOM cable to know for sure, or you can replace them as preventative maintenance and see if that helps.

It could be a plug issue. I doubt they're worn out if you got them done at the dealership recently, but I'd check to make sure they are gapped correctly and consistently across all plugs. There's a good chance the dealership tossed them in right out of the box, and some of your gaps could be way off. That might be what's causing your car to miss.

You might also have moisture in your tank. Can't hurt to try a bottle of HEET Marine formula in your tank to help get rid of any excess water that can cause drivability issues.

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What is this HEET stuff you speak of?

Nitrorea said:

What is this HEET stuff you speak of?

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It's an inexpensive fuel treatment which you add to the tank if you have moisture buildup in your gas tank. Helps absorb or dissipate water.

You need to clarify....

If it's a misfire, the ECU will record the counts, and post a CEL, and engine could produce misfire like symptons, such as 'bucking'.

If it's a lack of power, the ECU is applying fuel trims, and may NOT post a CEL

I just finished diagnosing my MK5 TFSI on lack of power. My fuel trims were really high, adding like 17% to 20% more fuel.
Turned out my air filter was absolutely plugged. Replaced it.... good as new;
"Warp 10 --- Engage"

Had same issue with this after I did stage 2. Went and did sparks, coils and MAF. Got it diagnosed at a shop and they found one of my injectors with some carbon on it not allowing it to fully spray. After a nice penny, my car runs with out misfire.

brmcm15 said:

Had same issue with this after I did stage 2. Went and did sparks, coils and MAF. Got it diagnosed at a shop and they found one of my injectors with some carbon on it not allowing it to fully spray. After a nice penny, my car runs with out misfire.

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Did they replace the injector(s) or just clean it/them?

In my case changing the lpfp didn't help so my issues are probably due to a faulty S3 injector.