WG erratic idle on startup

[JimmyJ]

Hi all,

I know this has a bit of discussion already but did anyone sort out the culprit?
I have an 04 WG which literally gives me a panic attack thinking about starting it every morning wondering whether or not I get to work or stuck on the highway in limp mode yet again! When it's on its game and the planets line up I still love driving it so I persevere. Plus it owes me a fortune lol

This months problem is a quite erratic up and down idle on start up. If left alone takes 30seconds to a minute to sort itself out, if I just touch the accelerator and hold it steady at about 850RPM it levels out within a few seconds then runs fine for the rest of the day, except once a while when it decided to increase the revs when I was pulling into a parking spot. Not ideal, but thankuflly has not done that again.

To possibly eliminate some of the suspects this is what has been done in the last 50,000ks

New injectors, rebuilt fuel pump, all fuel lines replaced (mechanic changed the set up to "something less troblesome" than the original.
New MAF, MAP. gearbox PCB, and multiple other bits and pieces that probably don't matter for this issue.

I'm wondering if possibly the TPS or IAC might be it. ??? IF that sounds logical does anybody have the part numbers or(at the risk of sounding silly) where they are positioned so I can see what I'm looking at when the 100 parts that "don't fit this vehicle" come up on google.

Many thanks

[JeanLuke]

Diesel? If so, the behaviour is fairly common because even at zero throttle the Injection Quantity is not zero. This is to give a soft return to idle speed. To check if this is the problem, repeat the experiment in low range. In low range the diesel uses a different fuel map which is zero IQ at zero throttle.

[JimmyJ]

Thank you for your reply.

Yes, diesel. So if it doesn't do it then what do you think would the problem be?

[JeanLuke]

It's a little normal. Does it do it in drive, or only in neutral?

You can remap the fuel to put in less IQ at zero throttle, but that's advanced tinkering. There is a thread on that.

Sent from my motorola edge 20 fusion using Tapatalk

[JimmyJ]

It only does it in neutral on start up. Then you can stop and start it all day and won't do it until it's sat overnight again

[JimmyJ]

I tried the starting in low range and interestingly enough it still did it but only very minimal (half a tacho needle width) and only lasted about 10 seconds.
Restarted in normal range, didt it worse than low but no where near as bad as normal. ????



OK scratch that I tried it again to show hubby and its gone back to doing it on 4L and normal. Must have been a fluke the first time

[JeanLuke]

Your "new injectors" and seeing this worries me a little. How much did you pay for the new injectors? Did the mechanic cut holes above injectors 4 & 5 to get access? If you are not seeing holes cut above these injectors and you were not charged for an engine removal, then I doubt new injectors were really fitted. How much do you trust this mechanic?

In H4 on the transfer case, the IQ is not zero at zero throttle. This is okay with new injectors. As they wear, they will let through a little more fuel. The non-zero IQ at 0% throttle position in H4 is enough with worn injectors to cause the revs to "hang" above idle. It's not a serious problem, though, if the revs return to idle in drive.

A few things to check. You need to set yourself up with WJ Diag Pro and a good quality ELM327 adaptor first. It's not expensive and very useful:

• Check the mechanic correctly programmed the injectors. WJ Diag does this. Look on the top of each injector for a 1, 2 or 3 in a circle and check the ECU setting matches this for each injector.
• Carefully look for evidence of holes having been cut above injectors 4 & 5. You might need to remove the wiper arms and the cowl grill to see. (While in there, replace the cabin filter on the left side.)
• Using WJ Diag, confirm the throttle position sensor is reporting zero at zero throttle. Sometimes the cable connection at the TPS can slip out and not let it return fully to idle. It's a simple fix. Put it back in.
• Using WJ Diag do the injector balance check (under engine tests). Do this both hot and stone cold and see if there is much difference.