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Discussion Starter #1
Hi everybody, so I have this problem for quiet a long time now and unfortunately a couple of shops I have visited can't solve it. When I starting my cold engine, for the first 30-40 seconds I have a very unstable idle. Engine runs like one or two cylinders are out and missfires. This only happens when outside temp is bellow 20 celcious and with cold engine. The lower the temp the wort the operation and from 15 degrees and bellow, operation is even worse . I get no fault code for this and I have change the MAF sensor with no success. I believe it has to do with a sensor but can't figure out which one. Any ideas are welcome. I will upload a video if you like tommorow to see what I mean.
Thomas
 

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We have seen problems with bad coolant temp sensors; cause this type of issue. On cold start up, you will get a rough idle and when revving, the engine can stumble with a rich condition (smoky exhaust and unburnt fuel smell). After the engine gets to normal operating temps; the engine will smooth out, regular idle and hesitation will disappear. Most of the time, a bad coolant temp sensor; will throw a trouble code but not always.

It is a good idea, to keep an eye on the coolant temp light in the speedo and see if it acts "normally". On cold startup, you should see a blue light and when it gets warm, the light should go out. There should not be any other type of modes shown.

Here are the modes of the coolant temp light:

Blue coolant light = engine cold
Flashing blue coolant light = fault in the coolant monitoring system
Flashing red coolant light = low on coolant
Steady red coolant light = engine overheating, pull over and stop engine IMMEDIATELY and do not run until the problem has been identified.

The might be other issues, that are fuel delivery or ignition related; could be a possibility, dirty throttle body (clean and do a throttle body alignment procedure recommended), low fuel pressure, failing coil, old plugs, etc. etc.

It is best to have a scan tool; that can show live data and that way, you can monitor, various things, such as coolant temps, maf readings, fuel trims, pending codes etc.

As for your MAF replacement; why did you replace it? Was there any related trouble codes; that would indicate it was faulty? It is best to monitor the MAF readings and that will indicate, if it is reading in spec. A replacement MAF, should be a oem BOSCH branded part; not a cheaper aftermarket MAF that will not work right, causing the car to run badly. If you have the old maf; you might reinstall it and see if the run any differently.

On these modern cars; a scan tool is crucial to see live data and note how things are running, that way you can see if anything looks off (e.g. fuel trims, maf readings, coolant temps, trouble/pending codes, etc.).

Fuel Trim Info - Ross-Tech Wiki

Start looking at your readings (fuel trims, maf, etc), checking for pending/trouble codes, check for a dirty throttle body, condition of your plugs, swap in your old maf and we can go from there.

A UK based service manual that covers your 1.6L engine; would be a good thing to purchase and that way, you can go over testing, troubleshooting procedures for possible failing parts. We do not have the 1.6L in the North American spec New Beetles; so, we do not have service manual info to refer you to.

The Haynes UK New Beetle service manual; seems to be a good and affordable option.


VW Beetle Petrol & Diesel (Apr 99 - 07) Haynes Repair Manual (Haynes Service and Repair Manuals) Paperback – 13 May 2013

Note: covers your engine: Hatchback, Saloon and Coupe, Petrol: 1.6 litre (1596cc),


ISBN-13: 978-0857336545

https://www.google.com/search?ei=gSD5WajSCIeJ0wKCj5r4Dg&q=VW+Beetle+Service+and+Repair+Manual+978-0857336545&oq=VW+Beetle+Service+and+Repair+Manual+978-0857336545&gs_l=psy-ab.3...26508.27491.0.28459.2.2.0.0.0.0.121.237.0j2.2.0....0...1.1j2.64.psy-ab..0.0.0....0.nXXJoJS2CnQ
 

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Discussion Starter #3
Thank you for the reply, well you have described my problem perfectly at your first lines, this is my case. Since I have installed in my car a scan gauge reader I can monitor live all engine parameters while driving, for the last ten years the blue light goes out exactly at 54 degrees, temp light operation is normal so I guess that my temp sensor operate correct.

''Other issues could be a possibility, that are fuel related or ignition; could be a possibility, dirty throttle body (clean and do a throttle body alignment recommended), low fuel pressure, failing coil, old plugs, etc. etc.''
I have recently replaced the ignition coil since it failed and I got the related fault codes. I have replaced spark plugs with no luck. Not sure about throttle body cleaning or low fuel press but I think that those could give me the same symptoms and above 20 degrees OT. But I will see what I can do about them. What is throttle body alignment?

''As for your MAF replacement; why did you replace it? Was there any related trouble codes; that would indicate it was faulty? It is best to monitor the MAF readings and that will indicate, if it is reading in spec. A replacement MAF, should be a oem BOSCH branded part; not a cheaper aftermarket MAF that will not work right, causing the car to run badly. If you have the old maf; you might reinstall it and see if the run any differently.''
One of the shops I visited he told me that I need to replace the MAF sensor because of the fault codes he had, I think the code was lean mixture or something but I don't remember. So I bought a new original Hitachi one as the one the car initially had but again with no luck. Then I visited another shop, they removed my new original MAF and test it with another one just to be sure but again no luck so my MAF is ok also I guess.
I was told that there is another ''cold'' sensor that read the intake cold air and that maybe this is the problem but I haven't checked that yet. On the other hand since I am able to reed the intake temp. I can tell you that this is stable and operate ok, on a cold day the intake temp is identical with the OT, as the engine gets hotter the intake temp also rises so this one also looks to be ok. I also run my car on LPG but this problem happens only at start up and only at gas operation, LPG operation is possible after 35 degrees water temp anyway.
Haven't checked my HAYNES manual to be honest but I will take a look if there is any ref in there.
Thomas
 

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I haven't worked on a 1.6L or have a manual; that I can look at but on the 1.8T here in the USA, the coolant temp sensors are known to fail. Your service manual; should have testing procedures for the sensor and you could confirm things are ok. The sensors, tend to not be very expensive and if you still are using a 10 year old sensor, it wouldn't' surprise me if it has failed after all those years.

Here is a video showing how the temp sensors fail:

https://www.youtube.com/watch?v=TwQ-2xp_TK4

testing:

https://www.youtube.com/watch?v=eXNBlH0c4_U

For your maf; I would confirm correct operation, using live data from a scan tool. As for using a Hitachi MAF; here we only see BOSCH as the stock oem for these but maybe VW uses Hitachi in the UK/Europe? Again, we don't have that engine; so, I cannot confirm this. If you were having a lean code; you could have other fuel delivery issues, that can cause that. Monitoring your fuel trims; can help you pinpoint if you have a possible weak fuel pump or vacuum leaks. Fuel pressure testing; would be a good way to rule things out, confirming things like the fuel pump/pressure are in spec.

As for LPG; are you referring to https://en.wikipedia.org/wiki/Liquefied_petroleum_gas?
Did you have a conversion added to your car; to run this? That could potentially add a whole other variable to troubleshooting your problem. I don't have a clue; how yours is setup or how your system is adapted to work with your 1.6L. I suppose, a failure or malfunction in that system; could pose a problem as well but maybe a LPG specialist shop, would be needed to check that out? Here is the USA LPG conversions; used to be popular on work trucks for industrial use with ranching, mining and the oil industry.

The throttle body cleaning, is easily done with some appropriate cleaner and then running a procedure with a VW specific scan tool. I usually use a "throttle body cleaner" from CRC and a old tooth brush, to get all the contamination from the assembly. If you don't have a vw scanner; you can try turning the key to "on" position without starting the car, wait a minute or so, until the noises from the throttle body stop. This is considered a "poor man's tba" and while up for debate, many consider this a alternative option to a tba with a vw scan tool.

http://wiki.ross-tech.com/wiki/index.php/Throttle_Body_Alignment_(TBA)

throttle body cleaner (CRC, GumOut, Wurth, Valvoline, Permatex, Liqui Moly, etc)

https://www.google.com/search?q=throttle+body+cleaner&oq=throttle+body+cleaner+&aqs=chrome..69i57.3285j0j7&sourceid=chrome&ie=UTF-8

You might read up in your service manual; how to test your coolant temp sensor and confirm it is ok and then possibly replace it, to see if that is the culprit. The manual, should have the coolant temp specs; when the coolant light goes out, fans kick on and what the "normal" operating temp range is.

How are your fuel trims (normal is usually + or - 10% range) and are there any pending codes?
 

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Discussion Starter #5
I am in a process of testing my water temp sensor and MAG according to manual instructions, so far I have the correct readings regarding the hot range, I just have to make some pins to test it properly. The LPG system is the one you linked, it runs parallel or seperatly from the gas fuel system with its own computer, anyway while engine starting this is disengaged. As for the fuel trims you mention I have no idea about it. Guess I need a diagnostic tool and a computer to test or check it.
I'll report back when I have something new.
 

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Ok, sounds good; a new coolant temp sensor, is probably not that expensive. Let us know, how the testing goes! Thanks! :)

PS: I'm not seeing for sure if the scan gauge II reads fuel trims for VW; you might look at VW specific scan tool. There are many "VAG" scan tools out in the marketplace; you might check out OBDEleven for a affordable option that runs on Android based devices or the Ross Tech VCDS for a mature windows based scanning solution.

https://www.scangauge.com/support/x-gauge-commands/volkswagen/ (you might email tech support and see if long and short term fuel trims are supported)

https://www.google.com/search?q=VAG+scan+tool&oq=VAG+scan+tool&aqs=chrome..69i57.3590j0j9&sourceid=chrome&ie=UTF-8

https://www.google.com/search?q=obdeleven&oq=obdeleven&aqs=chrome..69i57j69i60j69i59l2.1768j0j7&sourceid=chrome&ie=UTF-8

https://www.google.com/search?q=ross+tech+vcds&oq=ross+tech+vcds+&aqs=chrome..69i57j69i60l3j69i59l2.3000j0j9&sourceid=chrome&ie=UTF-8
 

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Discussion Starter #7
I measured today WC temp sensor and found it within limits as per manual (but i have it on the list to replace it anyway) Reading the manual, i found that there is also a cold start valve attached to the fuel injection pump. It is responsible of advancing the the fuel ignition timing during cold starts and a problem of it causes unstable engine idle!! Since the Fuel injection pump has a pulley i guess it is somewhere lower in the engine perhaps under the air conditioning pump. So i guess i have to jack up the car and work underneath. Work for the weekend is scheduled so ill let you guys know.
PS i love working on my 1965 fiat 500 which relaxes me but i hate messing with modern cars because all this little small Satan devices!! The magic is lost here.
Thomas
 

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Hmm, sounds like something unique to the 1.6L; never came in usa spec vw's, let is know how your testing goes, sounds like you may have found the problem! Thanks. :)
 

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Discussion Starter #9
Maybe not, on a second thought fuel injection pump is for the diesel version, I don't think that this engine has it and manual does not specify this. As far as I know this engine is the same with the 2liter 8 valve.
 

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Without a scan tool you are just randomly replacing parts and without data any diagnostic done would be nothing more than a guess. I have a vagcom and an obd eleven. I like the convince of the obd eleven but the vag com has features like graph logs as well as other features that make it a better tool for the more technical diagnostics. First and most obvious would be check and double check for a vacuum leak, If you have a scan tool check your long term fuel. This is a "average" of the fuel added or subracted in the ecu by modulating the injector pulses. When the codes are cleared the long term trims will be reset to zero and you may hear or feel a noticeable change when the engine is at idle. A positive fuel trim indicates un metered air, which could also be restricted fuel so rail pressure should be checked. If the pressure is low take a look at the fuel regulator and the filter. The negative long term fuel trim indicates unburned fuel which could indicate ignition or injectors. High or low trims could indicate problems with the o2 or the maf sensors so these numbers should be observer as well. Then when the engine is warm and the o2 sensor starts to cycle the ecu goes in to closed loop you can check the short term fuel. The trim should be +or- 10 or so negative or positive numbers above 20 will probably trip the mil and set a fuel trim code. The maf should be around 2or3 at idle if the maf readings look off clean the maf and recheck the numbers. The o2 sensor (bank1) should continuously cycle from 0 to 1 volt when the ecu is in closed loop, if the voltage does not change do an ohm check. Check the coolant temp and the ambient intake temp. Sensors and codes will only get you looking in the right direction then you test the components before you replace them. There are good inexpensive scan tools that can help diagnose problems efficiently and save you money that you would have needlessly spent on parts. Log your data before you clear your codes. After the problem is resolved clear the codes otherwise the car will have to be driven a few miles before the stored fuel trim will return to normal. When the codes are cleared the trim is reset. Don't forget the basics fuel, compression, ignition.
 

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Discussion Starter #12
Thank you for the detailed info and your time. I have to add that I changed the water coolant temperature and things are a little better now. Idle is not that rough and no more unburned fuel smell. Backfiring is also reduced and all this unstable condition last for 5-10 secconds. I say that problem is reduced by 50-60% But is still here. I will try and find a diagnostic tool possible from eBay and see what I can catch.
 

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Ok, sounds like your coolant temp sensor was bad; good job on the swap. Another thing that can cause a rough idle is a dirty throttle body; clean it and do an alignment.
Otherwise, as noted a vw specific scan tool that can do live data would be helpful in your troubleshooting process.
 

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For a vw scan tool; there are many "vag" versions on ebay/amazon (make sure they do live data not just read codes);. Just keep in mind, most offshore asian scan tool offer little to no support and if anything goes wrong, your usually on your own. If you go this route; purchasing through amazon, is a good idea with their good return policies.

Another option is obdeleven that is compatible with android devices (phones/tablets); has a downloadable app and a wireless dongle you plug into your obd II port.

https://www.google.com/search?q=vag+scan+tool&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

Lastly, the ross tech company sells vcds that runs on a windows pc; it is a well known, mature solution, that has true usa based support and registered user only forums to back up the tool. While it costs more than many other vw compatible scan tool solutions; it will pay for itself in its after sale support and wide use, familiarity in the world wide vw community. VCDS is compatible with the latest vw/audi cars and they offer free software updates; which is unheard of in the automobile repair industry.

https://www.google.com/search?q=ross+tech+vcds&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
 

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Hi All,
Recently i'm facing a problem When I starting my cold engine, for the first 45 seconds I have a very unstable.

still i couldn't find out the reason why its happening?

Please help from any one end.

Thanks....
 

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The above thread, has a lot of good troubleshooting info; you might start a new thread and discuss your problem more fully and make sure, to put it in the discussion area, related to your engine type. The failed coolant temp sensors; are one of the common, rough idle/cold start issues.
 

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Discussion Starter #17
It's been more than two years since I started this post and finally got my hands on the problem and solve it. Removed the inlet manifold replace all o rings with new (old where hard as plastic) and seems like problem is gone, propably intake was sucking air until seals got hot and became enought soft to seal. Now i have very stable idle. In a case someone facing the same problem maybe you should try this first.
 

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Thanks for the feedback; on the final resolution to the idle problem. I replaced the plastic injector cups with billet aluminum versions and rebuilt injectors and seals, i'm hoping a occasional erratic idle, will be solved, as well. In my case, a 1.8T AWP code engine.
 
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