Engine Hunts when warm :O(

[EvilScotsman]

Hi,
I just bought a MK3 2L 8v GTi, 1995, and I love it, after driving japs for years.

It has a few minor niggles but one of them I'd like to get some ideas on..

When it starts from cold OR hot, it barely catches, then creeps up to 1000rpm, once its there it revs OK.

When cold it idles smoothly at 1k, but when warm (oil temp 74 on the MFA) it 'hunts' up and down between 900 and 1000, sometimes blipping the throttle will cause it to stall here but not always. It pulls OK, I never abuse it, and it returns 28 - 29mpg ave (MFA 2).

The previous owner fitted plugs, dizzy cap, rotor arm, and timing belt (fitted by a fairly large local garage) so i guess they are out of the loop but what else can it be? I suspect an air leak or idle valve but don't want to dive in without some pointers.

I'm an electronics engineer and confident working on my cars but new to GTi's (or vw's in general)

Thanks in advance for any replies :O)

[patch900]

Had problem like this with mine - trouble starting, once started is fine.

Guys on here suggested ECU temp sensor. Guy at the garage ran diagnostic on it and it was ECU temp sensor.

The relays only cost ~£12 apparently but of course had to pay for them to run it as well but was getting the timing done at the same time.

Hope this helps

[boneybradley]

I would start at the ecu temp sensor as they are cheap and easy to fix (and work the gauge and ecu and cause problem's like you list)..... Next thing to check is all breather hoses as even the slightest air leak here can cause funny starting and running.....There are 2 relay's one for the ecu and another for the fuel pump and these can start to fail

Maybe this will help... it show's my ady simos injection model but most 95 onward are similar






On another note  don't take your car to a garage for the fault code's to be read as you can buy a reader from ebay etc for about £30 (just make sure it read's and clear's all codes from ecu,abs and airbag)

[EvilScotsman]

Thanks for the quick and excellent replies guys, especially the pics and diagrams.

That gives me good starting point. Someone else suggested cleaning the throttle body and butterfly as the egr valve dumps into the TB before the butterfly and gums it up wi crap?

Cheers again :O)

[boneybradley]

yeah the throttle body get's full of crap and sometimes can't fully close making the engine run bad.....again quite an easy job and not only solves idling problem's but also power issue's...I would normally say they idle badly with bad throttle bodie's rather then poor starting but they can also be a fix all!!!! and they are worth doing any how... I clean mine yearly

[patch900]

BTW, I think it was bradley who diagnosed my problem as ECU sensor  , so he knows what he is on about

[Len]

All the relays can be easily checked.

Warm up the car then turn off and remove ECU and Fuel relays if warm they are fine if cold to touch then replace.

Relays dont show up on fault code checks!

[EvilScotsman]

Cheers, i'll have a look at all that stuff tomorrow. Its bloody cold out at the moment tho an i hate workin outside in the cold but it has to be done!

btw what do you all get on MFA 2 for average fuel consumption? (I dont do long motorway cruising, maybe 15 miles at most but quite a bit of 2 - 6 mile journeys) - mine almost never reaches 30mpg :O( usually hits about 27

[boneybradley]

for fuel economy check out this thread  http://www.golfgtiforum.co.uk/index.php?topic=51764.0   and please let us know youre finding's with your fault.....

[EvilScotsman]

Cheers Boney, will do.

I'm also going to fit a full set of silicone hoses like samco or similar to get rid of any leaky old rubber problems now and in the future, plus they will make the engine look good! - (its not a very pretty engine anyway lol)