Hot starting problem

[Jez]

Morning all

I haven't been around much, v busy with my new job and buying a new house etc. I had no idea how stressfull buying a house could be!

Hope you guys can chip in with some ideas/solutions regarding an occasional hot starting problem with my 2000 S4. Since late last year there has been an occasional hot starting issue. Basically if the car has not fully cooled down after a run and I try to start the car again it will only just fire and requires a blip of the throttle to spring into life. It's almost as if it wants to idle at 300rpm.

A couple of times it's required a second cranking to get it started. This is only occasional, i.e perhaps 1 out of 10 hot starts.

Over past couple of weeks I've noticed the car is particularly jerky when lifting off the gas after a hot start. Pulls well, just 'bucks' when I lift off. After a couple of minutes this clears and it'll idle slightly high - 900 to 1000rpm.

I changed the spark plugs and did an oil change 2000 miles ago. The hot starting problem was apparant before I changed the plugs.

Other than that the car goes well... all a bit odd.

Sorry for the essay. Thanks in advance guys

[nickb834]

Have a look for the Idle Stabilisation Valve - not sure where this is on the S4, but I heard of something similar on an S2 that was down to the ISV

[dodgydave]

Have a look for the Idle Stabilisation Valve - not sure where this is on the S4, but I heard of something similar on an S2 that was down to the ISV

DBW (Drive By Wire) doesn't need or have such a valve!

[dodgydave]

Morning all

I haven't been around much, v busy with my new job and buying a new house etc. I had no idea how stressfull buying a house could be!

Hope you guys can chip in with some ideas/solutions regarding an occasional hot starting problem with my 2000 S4. Since late last year there has been an occasional hot starting issue. Basically if the car has not fully cooled down after a run and I try to start the car again it will only just fire and requires a blip of the throttle to spring into life. It's almost as if it wants to idle at 300rpm.

A couple of times it's required a second cranking to get it started. This is only occasional, i.e perhaps 1 out of 10 hot starts.

Over past couple of weeks I've noticed the car is particularly jerky when lifting off the gas after a hot start. Pulls well, just 'bucks' when I lift off. After a couple of minutes this clears and it'll idle slightly high - 900 to 1000rpm.

I changed the spark plugs and did an oil change 2000 miles ago. The hot starting problem was apparant before I changed the plugs.

Other than that the car goes well... all a bit odd.

Sorry for the essay. Thanks in advance guys

Sounds like gas building up in you fuel-lines because of the heat. Used to be a big problem on the old 10V Turbos. Something wrong along your tank venting system. I'd guess.

[SimonS4MTM]

Maybe a collant temp sensor and running rich

[Jez]

Thanks for the replies

Ever since I've had the car there's been a coolant temp sensor error in VAGCOM reported as intermittent. This remained post after-run pump mod, so must be another temp sensor or the wiring.

I used to have the same issue on one of my old digifart golf GTIs. A quick blip of the throttle round to 5k rpm used to sort it. Cleaning out the ISV, throttle body and idle screw would normally sort the high revving on the golfs, but does the S4 have an ISV (it is DWB btw)?

Will investigate the tank venting and sensors.

[yorkie]

Looks like you could have answered your own question, my money would be on the sensor which sits at the back of the block on the left side as you look at the engine from the front. It sends a signal to the temp gauge and the ecu.

[kevinw]

mine did exactly the same..... it was the coolant temp sensor. get it changed.

[Philws4]

IMHO this is a part that should be changed on any S4 that still has the 'older black' sensor still fitted but double check which part/terminal shape you need first as there are 2 that i know of: 059 919 501 & 059 919 501 A

Jez i reckon that you will need the 059 919 501 A sensor,which was the same as mine due to the fact that the car is a 2000 MY.

[Philws4]

IMHO this is a part that should be changed on any S4 that still has the 'older black' sensor still fitted but double check which part/terminal shape you need first as there are 2 that i know of: 059 919 501 & 059 919 501 A

Jez i reckon that you will need the 059 919 501 A sensor,which was the same as mine due to the fact that the car is a 2000 MY.

[Philws4]

IMHO this is a part that should be changed on any S4 that still has the 'older black' sensor still fitted but double check which part/terminal shape you need first as there are 2 that i know of: 059 919 501 & 059 919 501 A

Jez i reckon that you will need the 059 919 501 A sensor,which was the same as mine due to the fact that the car is a 2000 MY.

[Jez]

Picked up a new sensor this afternoon from the stealers... £27! I haven't changed it over yet, so couldn't comment on the colour of the old sensor, but the new one is green. Finger's crossed, but this could possibly cure that intermittent temp sensor fault in VAGCOM as well as the starting problems

Thanks for the input and I'll report back with my findings.

Jez

[Philws4]

Oops sorry about the triple posting!!!

[Jez]

Evening all

Had a productive afternoon after work and fitted the new temp sensor as well as the DTS I had lying around. The old temp sensor was a git to get out...positively welded in place, but once replaced the car starts as it should when hot and the idle appears smoother too! Time will tell if it's sorted the slight jerkiness.

And for the DTS... marked improvement and compliments the short shifter well. Well worth lying on my back for an hour and a half grazing my hands

Cheers all.

[mad-for-tar]

I changed the coolant temp sensor on mine the same time I did the after run mod. Coming home from work the odd evening, used to see the coolant temp gauge drop from 80 degrees back to 60 and then slowly climb back to operating temperature. Also noticed a cut in power when I opened the throttle. After changing this sensor, the problem disappeared completely, runs sweet now!