Rough idle when cold - new ideas needed? Wits end!

[cornishkez]

I know this subject has been done to death, believe me I've spent hours trawling forums reading up on the subject! So I appreciate you humouring me and any advice is gratefully received!

I've just bought a mk4 tdi 1.9 2002, 110k on the clock from a local dealer.

From day 1 it has had a rough idle when cold. The car starts on the flick of the key and run perfect for anywhere between 10-20 secs then it starts to play up. It will splutter and sounds for an instant like it's going to stall, then picks itself up again, puffing out a cloud of white smoke. It repeats this continuously for a couple of minutes minutes and eventually stops. The rev counter only moves about 50rpm and it dips rather than rises. It idles at 950rpm. Once it's stopped it runs fine and the issue only happens from cold. It has to sit for 4 hours or so before it will do it again. If you hold the revs above 1200ish it stops it.

The second issue, not sure if it's related or not is that when driving, usually between 1800-2200 and under light acceleration or when maintaining a constant speed but climbing a hill, the engine will hesitate, splitter and clear through (followed by a puff of white smoke). It feels like the momentary drag you get when hitting a deep puddle. This happens every few minutes but there have been times when it has been doing it every 10 secs or so.

I never get black smoke (unless I purposely blow build up out the back), the smoke is always white.

There is no sign of coolant leaking, the exhaust fumes smell like fuel, can't say it smells sweet to me?! Found a air leak coming from the fuel filter, replaced the seals and it's now priming properly. Ran a bottle of comma diesel magic directly from the filter. The garage cleaned the egr, made no difference. Not sure if they touched the throttle body and lower pipe?

The only code I get is an intermitant temp coolant sensor (backed up by an intermittent temp gauge).

Timing belt was done 3 years and 30k miles ago.

Glow plugs don't throw any codes but a couple of odd dash readings suggests they might not be up to scratch. Sticking on when engine is up to temp.

My plan is to replace the cts this weekend and clean the Maf sensor, can do the glow plugs as well. Timing belt will be a job to do in the near future.

Am I on the right track?!

[cornishkez]

New thing happened this evening, the car didn't clear through like it usually does, the splutter got weaker and faster to the point where it sounded like it was pulsing. When I applied gas, the rev reluctantly climbed but bounced up between the splutters. I couldn't drive off as the revs were so slow to respond. I restarted the car and it cleared through, but really limped home. It didn't go into limp mode but was very lacking in power.

idle air control valve?

[herby0001]

My immediate thought (only from what I've read on the forum, not personal experience) was a worn camshaft. From what I remember, the chocolate cams on ARL 150PS engines gave these sort of symptoms of poor running after starting. Changing the CTS is a good start though, especially when it's throwing up a code. I hope it's not a cam issue as it's a pricey fix, especially if you want it done correctly with proper VW parts. Strangely, the coil symbol can mean other things, eg. a flashing one can mean a faulty brake pedal switch. Weird, I know.

[Doctle Odd]

Can you get a scan done with VCDS and post the results?

[cornishkez]

Thanks guys, I hope it isn't a worn camshaft. How would I know if this was the issue? No codes were picked up on the diagnostic, either by the garage or my friend. Not sure what diagnostic he's got, but it does all makes of car's so would that suggest it isn't VAGCOM? I'll find out from him if it has 'logging' capabilities. If not, is there a way of finding someone locally who can? ie is a tuning company likely to? or would I have to go to a dealership?

[Doctle Odd]

It could be any number of things from an injector loom to a crank sensor but you need a people scan. A scanner that works on "all" cars isn't the best for a VAG car, read this link. Ross-Tech: VCDS: DTC Comparison A proper scan with VCDS will rule out sensors timing boost etc. You need 10 posts to contact a member. Here is a link to the members with VCDS page VWAF User Location Map - VCDS - Google Maps someone might contact you or you could ask a mod to contact someone near you on your behalf.

[cornishkez]

Quick update - have changed the CTS, temperature guage now works but made absolutely no difference to the rough idle on cold start. Didn't clean the MAF sensor, got scared!!! Had a nose while the air intake was off, not sure what I am looking at to be honest? Which is the bit that I should spray clean, is it the square mesh? Or is there a wire further inside? The square mesh looked a little bit corroded around the edges?

I think I might have a lead on a local garage with a VW enthusuast mechanic, who has VCDS.

[cornishkez]

Also, it's only 100bhp engine, not the 150bhp. Does that make worm camshafts less likely? I've seen a camshaft kit on ebay for £179.00, is that a fair representation of the cost? I assume it will be a labour intensive job and the labour will cost as much as parts?!

[Doctle Odd]

Cleaning a MAF sensor is likely to either do nothing or ruin it. Get the VCDS scan 1st

[cornishkez]

I'm glad I just logged in on the off chance someone had replied...I was just geeing myself up to go out and have a go at the maf. I'll leave well alone and get on the phone to the local dealer I bought it from first thing in the morning. Will try and track down the elusive vw guy with VCDC as well. I have zero faith in the local dealer now, but seeing as I've had the car less than 2 weeks, don't feel like I should be having to replace sensors or seals myself. Especially when they told me it was code clear, but when I run my own it's not.

Thankyou!!!