Rough idle on cold start

chmarshall81 · Post by **chmarshall81** » Wed Apr 05, 2023 7:00 am

Hi guys

I have a 2015 Polo TSI. Took it for a cam belt service, which they messed up. Had to take it back 5x before they improved the problem. Each time I got my car back, they claimed the timing was perfect, and that it might be something else causing the engine to randomly run rough (coils, mountings, wiring to coils). Eventually had to pay someone else to get it perfect a couple of months later. In the meantime, water pump went, which had to be replaced.

Only one problem remains: a rough idle at cold start with a huge consumption increase (4,7l/100km) and revs up to 1100 for a few seconds before it settles down.

Sometimes the cold start was normal (smooth idle, up to 1,5l/100km and revs up to 900), but those times are very few and far between.

Spark plugs were obviously fouled during timing out period, so got them replaced. Replaced air filter, petrol filter, coils, Map sensor, Wynns O2 sensor and CC cleaner, a few bottles of injector cleaner). Use CRC intake valve cleaner and dis another oil change (7 months later). But cold start rough idle persists. Engine runs smooth when warm.

Took it to 4 different workshops for diagnostics, but no joy. The last one told me it was carbon build up on inside of injectors, causing one or more to not close properly and leak a tiny bit, hence the surge on cold start.

Any advice before I fork out even more money?

I can imagine the injectors were fouled during that time, but the 3 bottles of injector cleaner should have done the job and I’m not paying R3000 to clean them as was quoted.

Any advice would be much appreciate!

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PapaJo · Post by **PapaJo** » Sun Apr 16, 2023 10:08 am

Was the rough idle present before the initial cambelt service?

Check the pcv circuit piping for any leaks and cracks.

chmarshall81 · Post by **chmarshall81** » Sun Apr 16, 2023 1:00 pm

No it was only after the timing belt. I am suspecting carbon build up on intake valves after doing a bit of research, but will check out the pcv valve. Thanks for responding!

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Kenz_0 · Post by **Kenz_0** » Mon Apr 17, 2023 5:15 pm

Man, I have the same symptoms, I checked everything you checked and did the walnut blasting and injector recon, everything passed the tests but the problem remained. If you have a rough idle on cold start with a whistling type sound which settles after the first minute or 2, then it's most likely a bad PCV valve

chmarshall81 · Post by **chmarshall81** » Tue Apr 18, 2023 4:33 am

Thanks very much! I will definitely check that out and get back to you!

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chmarshall81 · Post by **chmarshall81** » Tue Apr 18, 2023 5:58 pm

So I just need to make sure that I’m on the right track… so you’re talking about the non-return valve as shown here? Is there a trick to removing it?

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chmarshall81 · Post by **chmarshall81** » Wed Apr 19, 2023 5:18 pm

Also, when I removed the pipe and placed my finger in front of valve opening, I could feel it sucking in air. When I closed the valve with my finger, I could hear a nasty whistling noise. Is it supposed to suck in air from the air filter box?

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PapaJo · Post by **PapaJo** » Thu Apr 20, 2023 10:36 pm

Find that whistle and fix it.

Jeffery+1 · Post by **Jeffery+1** » Sun Apr 23, 2023 10:01 pm

Good evening guys, I am new to the advise chat...I am having the similar issues, also just had the cam belt, tensioner changed by an RMI approved workshop. Took it back they advised that the coil packs need replacing as it is a common issue on the Polo Tsi 1.2, never had an issue before have the service and cambelt change done.
My main issue is the pulsing idle, and jerk at low RPM.

chmarshall81 · Post by **chmarshall81** » Mon Apr 24, 2023 4:28 am

Hi Jeffery
Rev it up to 2000 while stationary, if it jerks heavily then the timing is off. That’s what happened to me.
If that’s the case, then the mechanic didn’t use the locking tool to set timing. I don’t recommend taking it back to the people that couldn’t get it right the first time. There’s plenty of vw specialists that can do it as they have the tool. I got mine reset for R700. Just make sure they have the timing set including that locking tool.

Don’t buy any parts yet.

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chmarshall81 · Post by **chmarshall81** » Mon Apr 24, 2023 4:34 am

Also, don’t bother going to the VW dealership. They wanted R6K to reset the timing

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Jeffery+1 · Post by **Jeffery+1** » Mon Apr 24, 2023 12:57 pm

Thank you

chmarshall81 · Post by **chmarshall81** » Sat Jun 17, 2023 9:25 am

Update. Some few thousands of dollars that I had stuffed under my couch later…

Did the carbon cleaning of intake valves and ultrasonic injector cleaning (although not with the workshop that quoted me that time). Turns out the oil separator’s vacuum pipe connector was broken (I assume by the people that took off the manifold to inspect the injectors, could be wrong). Got it fixed. Problem not solved.

The “RMI” guy who did my timing a second time overtensioned the tensioner that time. It was loosened but bearings were messed up already.
The tensioner was making a noise and was a worry for me, so decided to go to my new favourite technician and redo the timing completely. He discovered that there was a lot of play on the camshaft pulley and found that where the camshaft touched the head, it was worn. Replaced that (a few more dollars from the couch). Problem still not f@!$ng solved.

Found a faulty spark plug in between, problem NOT solved. The replacement ignition coils (2nd hand) started giving me consumption and misfire issues, so I’ve ordered new Beru ones. Also ordered a new MAP sensor. I found that when I remove the MAP sensor, my cold start issues are not there. Whether MAP is the cause or it’s readings a symptom remains to be seen. I bought a secondhand one, worked perfectly for a week, then problems.

Bought a scantool and low and behold, my O2 sensor 2 is following sensor 1 up and down. So all this running rich has now clogged my converter I deduce. At this point I’m fed up and broke. New coils and map better solve my cold start issues. I have an idea of what to do with cat, but it’s not going to be nice…

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Mike2 · Post by **Mike2** » Thu Dec 21, 2023 10:00 pm

Hi sir good day any feedback with regards to rough idle on cold have you sorted it out yet? Would like to know thanks you

chmarshall81 · Post by **chmarshall81** » Fri Dec 22, 2023 5:17 am

Hi. It was the coolant temperature switch on radiator outlet. Was reading -40.

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