Sparks at start-up.. immediately dies.. HELP :(

[sharki786]

is your air filter not blocked by any chance? try starting it without the airbox attached. if still same problem i would try a differnt thottle body.

[xAntiVenxm]

is your air filter not blocked by any chance? try starting it without the airbox attached. if still same problem i would try a differnt thottle body.

yeah air filter is clean, checked the induction hose and its not blocked, the air feed into the throttle body is also clean..

i didn't put the box back on when i started it just before, the induction hose was detached as i also wondered about the airflow..

whats the thinking, throttle body is somehow faulty? or potentiometer? or the other sensor on the back?

should i also replace the throttle cable mounting?

[sharki786]

take the big pipe off going to the throttle body and get someone to turn the ignition on and see if the throttle body flap moves, if not then try starting it without touching the pedal if it still dont move then do what you do to get it to start. if the flap doesnt move at all the best thing to do is replace the throttle body and do what i told you in my 1st post, turn ign on for 30-60 seconds DO NOT TOUCH THE PEDAL, turn the ign off, take key out, put key back in turn ign on wait for the lights to go out then start it. let us know what happens

[itavaltalainen]

If you have vcds then you can use measuring blocks to look at various engine parameters - so go in there with igntion on but engine not running. Then look for the correct measuring block (for a mk3 pretty much all should be labelled) and see if the potentiometer (throttle) values goes up and down smoothly and if the idle switch is detected OK.

[Len]

Have you checked ALL the vacuum hoses? inc. the one up to the ecu? Making sure none of them are pinched

[xAntiVenxm]

Have you checked ALL the vacuum hoses? inc. the one up to the ecu? Making sure none of them are pinched

Yeah I replaced the long one that is on the back of the throttle body which goes through a rubber grommet to behind the engine back under the windscreen where there is a large box-shaped object (presuming it's the ECU) as it was cracked and dead - No change

Throttle body seems to be working fine as well..

When I get it to start up by hitting the pedal, it fires up no issues and goes all the way through the rev range.. and is sensitive enough to changes in accelerator position to make me believe the potentiometer is functioning properly..

NO error codes on VCDS still..

getting really annoying.

Thing I have noticed - Where the Accelerator cable connects to the throttle body, the plastic body it's connected to has what looks like a tiny button on the back.. Which I thought would make the engine go into idle when the accelerator is released, and the cable mount relaxes back to push it.

Seems as soon as that happens, the engine dies.

Could the Idle control valve at the front of the intake pipes be broken?

It looked totally clean when looking at it, no hoses blocked..


but I am seriously out of ideas

[xAntiVenxm]

Going to give it another thorough look over..

found a link on another website with common issues and it says the ECU can get locked, or disabled due to poor earth contacts.

being that my golf sat in a barn for a year before I got her, and then a garage after I did, I wouldn't be surprised if she has corroded contacts somewhere or everywhere.

There's a big black earth wire, wide and flat, coming down from behind the bonnet carpet.. it's been snapped off.

Anyone know if that's the ECU ground? might be my issue!

Will get home and connect it back up and see if that fixes it this evening.

[itavaltalainen]

When I get it to start up by hitting the pedal, it fires up no issues and goes all the way through the rev range.. and is sensitive enough to changes in accelerator position to make me believe the potentiometer is functioning properly..

NO error codes on VCDS still..

Have you finally checked the measuring blocks in VCDS??

Only because engine reacts to throttle does not mean potentiometer is working correctly in all positions.
The potentiometer has a conductive layer and a brush.... now they are permanently mating, so you have friction and wear. Over time the conductive layer (often carbon) will wear away and leave bald patches, which result in open loop.... The ECU may not pick this up on a fault (Mk3 OBD is very basic) hence check measuring blocks and see if the response from potentiometer is OK. GND fault is not very likely if it communicates with VCDS OK.

[xAntiVenxm]

When I get it to start up by hitting the pedal, it fires up no issues and goes all the way through the rev range.. and is sensitive enough to changes in accelerator position to make me believe the potentiometer is functioning properly..

NO error codes on VCDS still..

Have you finally checked the measuring blocks in VCDS??

Only because engine reacts to throttle does not mean potentiometer is working correctly in all positions.
The potentiometer has a conductive layer and a brush.... now they are permanently mating, so you have friction and wear. Over time the conductive layer (often carbon) will wear away and leave bald patches, which result in open loop.... The ECU may not pick this up on a fault (Mk3 OBD is very basic) hence check measuring blocks and see if the response from potentiometer is OK. GND fault is not very likely if it communicates with VCDS OK.

do you have any sort of guide on how to use vcds to test this??

[Len]

That strap you mention is only the bonnet earth mine snapped years ago and has never caused any issues.

You could try disconnecting the battery, which will reset the ecu, leave it off for at least 5 minutes with both terminals off and away.