Rough starting/running when warm

Right, hoping the wizards on here can shed some light on a frustrating issue I've been battling with for the last month or so in my 1.9 TDI BXE Golf.

Symptoms are:

When cold in the morning, car will start 1st turn of the key, idles fine, drives nicely, gets up to temperature reasonably quickly, minimal black smoke at start, no issues.

When warm however, it shudders quite badly when starting, sometimes taking 3 or 4 turns of the key and cranking before it will catch. Also when warm (ie: after a reasonable drive) and tackling a hill and changing down to 4th so as not to "lug" the engine, I have what I can only describe as a stutter, feels as though as though the engine has a small misfire and loss of power and then it picks up and carries on driving normally.

So far I have:

Checked for errors with VCDS, got a steering wheel malfunction, intermittent fault in ignition switch. New switch was ordered and duly installed, now no more errors but the issue persists.

Checked the torsion value, sitting on -0.5

Checked the in tank fuel pump for any blockages in the pickup, checked fuel pump wiring, ran the pump using VCDS, all looks to be in good working order.

Serviced the car, replaced all filters and changed oil.

Checked the injection quantity deviation, all OK, ranging from 0.34 to 0.17, seem to balance OK.

Had the battery tested, guys at the local battery place reckon it's fine. Swapped with a loan battery just in case, issue persists.

Removed and stripped the starter motor, cleaned the commutator, checked the brushes & planetary gears & wiring, all looked OK so re-installed it.

Changed the coolant temperature sensor.

Checked the intake manifold flap for operation, seems to be working fine.

Removed, cleaned and reinstalled the camshaft position sensor (I read they are magnetic and can pick up dirt).

Ran a can of Liqui Moly Diesel Purge through it.


Despite all of the above, I'm still battling with warm rough starting & occassional "stutter".


DMF and cambelt were done less than 10,000km ago, gears engage fine, clutch action is smooth, clutch bites nicely. Zero noise from the DMF.

Camshaft and lifters were replaced 40,000km ago, have been using Liqui Moly 4100 oil ever since - it's 505.01


Is there anything else I should be looking at? I did read about wiring harness chafing and checking the MAF but surely if there was a fault there it would battle to start & run regardless of hot or cold temperature?


Would appreciate any advice before I take a rag and a match to it!

Thanks
Craig.

CraigZA said:

Is there anything else I should be looking at?

Click to expand...

Wouldn't hurt to check fuel temps, and compare readings between hot and cold starts. Maybe you have a flaky fuel temp sensor? I'm just guessing, since I didn't see it on your list.

This is a well-known "hot start problem" on VW engines.
An ECU reflash is needed. Visit a local tune shop and ask them for that.

At above certain coolant temperature, the fuel isn't being injected below 240-280 RPM range ( I don't remember exact RPM).
The fuelling map needs to be amended in such way so that the fuel is injected at lower RPMs even with warm coolant.

OK - will check the temps, supposedly coolant and fuel should be similar?

Any idea what the certain coolant temp is where fuel is not injected?

I don't remember.
To confirm that my facts are true, you can disconnect the coolant temperature sensor which is on the flange near the cylinder head, at the air filter side and try to start the engine. It will start instantly.
Don't waste you time and money futher, visit a local tune shop and ask if they can do that. If they are professionals, the'll know what you are talking about.

I have been having a similar problem with my 2005.5 PD TDI. When starting hot it shudders and rattles like it is running on 1 cylinder. It then stalls out after 1-2 seconds. Usually on the second attempt it starts and runs fine. One mechanic said it was the balance shaft. Then the dealer said to replace the fuel filter (it was only 5K miles old) and that did not fix it. They suggested a $1400 intake cleaning which I have not tried. I did remove the temperature sensor at the intake side and the problem still occurred. When it is running it is great with no issues. This only happens when it is hot.

Sounds similar to my problem starting and stuttering on highway, but mine doesnt always start first time cold, very similar symptoms(my post is the intermitent hard starting one) i'll be keeping an eye on this thread to see what fixes yours. Did yours just start recently?

Sorry i missed that you said a month ago, besides what youve done already i was told leaking injector seals could be a possibility

markweber said:

I have been having a similar problem with my 2005.5 PD TDI. When starting hot it shudders and rattles like it is running on 1 cylinder. It then stalls out after 1-2 seconds. Usually on the second attempt it starts and runs fine. One mechanic said it was the balance shaft. Then the dealer said to replace the fuel filter (it was only 5K miles old) and that did not fix it. They suggested a $1400 intake cleaning which I have not tried. I did remove the temperature sensor at the intake side and the problem still occurred. When it is running it is great with no issues. This only happens when it is hot.

Click to expand...

It's not the intake so definitely don't give the dealer $1400 & then have the same problem. Most likely issue is the engine wiring harness. 2nd check would be the cam.

"Starts OK when cold but struggles when hot" is a common sign of a malfunctioning crank sensor, if memory serves.

May or may not throw a code... and sometimes it's the wiring to the crank sensor that's the issue.

But if it's really temperature-dependent... my money's on the crank sensor.