Air/Fuel/Sensor problem mk3 16V ABF

[Splinter]

Doing some general work on my ABF 16v engine last night, put it all back together now 'small' problem.

Idle's perfectly, but when revved, it gets to about 3,500 apx. and cuts back down to idle again. So if you Hold the throttle open it sound as if you're constantly revving it up and down. Pulled the very small pipe off top of manifold which helped it free rev, but injected through twice as much fuel then and popped through the exhaust.   

What sensor/pipe/valve's causing my problem? Any help much appreciated, hopefully I've not broken anything!

Are there any general engine diagrams available on the net. I really should get a Haynes manual 

[Overseer]

hayne's is utter wank for a mk3 valver mate


first obvious question.. exactly what did you work on?

and second.. i'm not quite sure of your symptoms.. you say if you have it WOT it fluctuates?


did you take off the throttle body or mess with that kind of sh!t in any way?

[Splinter]

I was only replacing the leaking rocker cover gaskets, spark plugs, oil change, engine clean up. One of the rear bolts rounded which I've sorted so that stressed me out at the time. Don't think they'd ever been removed before.

I removed everything from the inlet manifold, didn't open up the throttle body, but did unscrew the little plastic part from the front of it held on by two philips torx screws. (sorry I'm vague about the engine parts, not had it that long) Could it be this not quite fitted back correctly or something. Would help if I had a basic diagram.

Like I say, it idles smooth, but when throttle opened it's cutting the revs back, (then they go back up again, then cut back again), so it sound like I'm just revving it on & off, when it should be constant revs.

[Overseer]

ok. i'm pretty sure what you removed from the throttle body was the throttle position sensor so my money is on that.



the only way to get a decent diagram is to get as dodgy copy of the ETKA.

there are no good resources for the mk3 16v

[Splinter]

Thanks, I wasn't wiv it yesterday as my girlfriend went to hospital through the night and I've not slept! but she okay now. 

Thinking about it today, it must be the throttle switch/sensor. Thought I put it back right but maybe not. I'll have a look when I get home.

Think I've ordered the ETKA (or something similar) for PC, but it hasn't arrived yet. Hopefully that'll help me out in future!! Try not to use garages, can't afford it!

[Splinter]

Right try again  -  throttle position control/switch definatly seems to be fitted okay.

I tried it unscrewed (but plugged in) and gently manually turning the position of the contol with a small screwdriver while revving. It seems to make no difference, but it does feel a little lose inside the plastic housing, could it be broken? 

The microswitch throttle sensor behind the throttle body/manifold is clicking on and off with the throttle okay.

[mk1]

OK, there are three wires going to the throttle sensor, brown white is -ve, red white is 5volt from ECU and red blue is the signal to the ECU. Check the earth and 5v then check that when you open and close the throttle the red/blue value changes between .6v closed and 4.1v fully open.
Hope this helps.
Steve.

[Splinter]

The front throttle sensor is okay electrically. Its actually 1500 rpm it wont rev above. ECU just seems to cut power out -  back to idle speed.

[Splinter]

found it!    with help of multimeter.
 Got some bad wiring going to the rear throttle sensor (that runs along back of manifold)