over revvvving mk1 golf gti

[new_gti_owner]

can anyone one help recently bought a mk1 golf 1800  8v gti y reg with immobiliser on start up revs up to 5000 revs then for a few seconds drops down to a 1000 revs popping and banging then up to 5000 revs again and back down to 1000 again popping and bagging this happens 7 or 8 times then pops and bangs at around 1000 revs if i then touch the trottle its straight back up to 5000 to 6000 revs I have fitted new spark plugs leads and dizzy cap rotor arm and air filter the air filter box has 6 to 8 2p size holes in the bottom please help

[harr1s]

welcome to the site .
the holes sounds like someone has drilled the box to improve air flow, some people say it makes an improvement some say it dont. this shouldnt effect the car on start up like youve explained .might be something to do with the warm up valve richandhazel will proberly know  he'll reply when he see's the post

 cheers...

                harr1s

[new_gti_owner]

thanks any advice will be much appreciated    thanks andy

[richandhazel]

Hi 'new_gti_owner', welcome to the forum.
Thanks for the vote of confidence there Mark, I'll do my best to help, although this sounds like an odd one :-/
I think the first thing I would be tempted to look for is a vacuum leak somewhere, possibly a bad one. Check the condition of all those vacuum hoses and pipes, if they're drawing in air they could be messing up the rest of the system which is in turn attempting to compensate.
Also, have a quick check and make sure all the injectors are seated correctly. I had an injector that, for some reason, had pulled out and the car behaved almost exactly the way you just described only it was very difficult to get it to idle at all!
I'll have a look in my books later and see if I can find anything else that might help.
As Mark says, those holes in the box are a common mod to improve airflow and shouldn't be causing the problem.  
Good Luck, you don't need that thing revving up like that on a cold engine

[richandhazel]

I dug this out:-

http://members.lycos.co.uk/richandhazel/K-jetronic%20injection/index.htm

I think its a better illustration than what you'll find in the Haynes manual. I think you have an air leak downstream of the sensor plate somewhere.
If you can't find an airleak then maybe its worth testing some of the auxillary components, as Mark suggested. I think the haynes manual does cover the tests but if you need more info give me a shout.

[new_gti_owner]

cheers I will have a mess thanks   andy

[new_gti_owner]

had a good look round the engine bay,it feels that one of the injectors castings on the manifold that there may be a piece missing.When I pulled that injector out the engine seems to run a little smoother on 3 cylinders.will the 1600 and the 1800 manifold be interchangable.many thanks andy P.S It may take me alittle longer to reply as I am using my sisters computer and she is passing on your replys  

[richandhazel]

The injectors push in to plastic inserts that are screwed into the cylinder head. You should simply be able to unscrew the old insert (I think its a large allan key you'll need) and replace it with a new one. The injector should have been a pig to remove so if it came out quite easily, thats almost certainly where your problem is.
This diagram shows what I mean:-

http://members.lycos.co.uk/richandhazel/Injector.htm

Don't forget to get a new O-ring for the injector too

[new_gti_owner]

cheers for help will past on to my bro and he will get back to u thanks again  amanda x

[richandhazel]

Anything to try and help, BTDT helps everyone, thats what its all about.