MK4 Golf Startting issues

[fergusfp]

Hello everyone, I have a MK4 1.6 golf. It has a problem when it is started, every 6 out of 7 starts (on average) has an extended crank period before it fires up and when it does, the idle is rough. If I drive it in this state the car will surge all the way up to 60mph and then be (OKAY) at crusing until there is a sudden drop in power and a jolt through the car.

I have taken it to the garage and they have replaced a spark plug, checked work they did on the throttle body and replaced the timing belt that we thought might of stretched, and replaced the crank sensor.

When you get to that magic start (one in sevenish) the car will run great.

Does anyone have any ideas where I can start diagnosing this problem. The garage said not to ring them again, they will ring me but that was over a week ago now.

Any help would be really appreciated

Thanks

[Oscar011]

fergusfp said:

Hello everyone, I have a MK4 1.6 golf. It has a problem when it is started, every 6 out of 7 starts (on average) has an extended crank period before it fires up and when it does, the idle is rough. If I drive it in this state the car will surge all the way up to 60mph and then be (OKAY) at crusing until there is a sudden drop in power and a jolt through the car.

I have taken it to the garage and they have replaced a spark plug, checked work they did on the throttle body and replaced the timing belt that we thought might of stretched, and replaced the crank sensor.

When you get to that magic start (one in sevenish) the car will run great.

Does anyone have any ideas where I can start diagnosing this problem. The garage said not to ring them again, they will ring me but that was over a week ago now.

Any help would be really appreciated

Thanks

Have you scanned the car for any codes? Even if no warning lights are on usually there will be something stored. You say they have also changed the throttle body?

[colin_p]

What engine is it?

The 1.6 came in two main types; an eight valve and a sixteen valve.

[fergusfp]

Colin and Oscar thank you get getting back to me. It is the 1.6 sr which I assume is the 8 valve.

The garage checked the codes and said there were no logged faults. However I should double check myself. Unfortunately my machine is with a friend who is a bit of a dive away so I will see if my neighbour has got one I can use after work.

I bought the Golf a month ago from the local Garage. They did work on the throttle body for its MOT, before they sold it to me. That was the first thing they checked, but apparently all in good shape.

Thanks

[Mr2Mike]

A dying cam sensor can cause these symptoms. If the ECU doesn't see a pulse from the cam sensor it takes longer for it to sync itself to the crank during starting, idle is rougher and power will likely be down a bit as well.

[colin_p]

When doing anything on the throttle bodies on these, mainly cleaning, an electronic alignment needs to be carried out afterwards. And not only that the previous learnt values need to be erased prior to the alignment unlike on many other cars where the alignment process can be done straight away.

But as above, some code logging and or live data runs would be best to diagnose this type of fault.

[Oscar011]

colin_p said:

When doing anything on the throttle bodies on these, mainly cleaning, an electronic alignment needs to be carried out afterwards. And not only that the previous learnt values need to be erased prior to the alignment unlike on many other cars where the alignment process can be done straight away.

But as above, some code logging and or live data runs would be best to diagnose this type of fault.

Throttle position sensor?

[colin_p]

Oscar011 said:

Throttle position sensor?

It has been a long time since I worked on one but I recall the 8v's having a cable throttle. That said, I recall the position sensor is part of the throttle body assembly.

If the ECU doesn't know the base value / angle, it can play havoc with all sorts of running and driving issues.

As with any online armchair diagnostics, they are always a best guess.

[Oscar011]

colin_p said:

Oscar011 said:

Throttle position sensor?

It has been a long time since I worked on one but I recall the 8v's having a cable throttle. That said, I recall the position sensor is part of the throttle body assembly.

If the ECU doesn't know the base value / angle, it can play havoc with all sorts of running and driving issues.

As with any online armchair diagnostics, they are always a best guess.

Hi Colin, let’s say it does have a throttle position sensor. Even know I’m pretty sure you’re correct it has a throttle cable. If the throttle position sensor was at fault would you replace it with a new sensor or would it be a whole new throttle body due to the sensor being part of the throttle body or even adapting the sensor so that the ECU knows the correct values (like vcds)?

[colin_p]

If you have access to VCDS then I'd start by checking for fault codes, then;

Electronically aligning the throttle body (after erasing the previous learnt values).

Then if no better, I'd then go on and do some live data logging.

Do not buy anything until you have diagnosed the fault.

[fergusfp]

Hi Guys

There is defiantly a cable on the throttle body. Thank you very much for your help so far. I will try get ahold of a diagnostics machine over the weekend and see what I can figure out. Will keep this thread updated.