bizarre high revs at start-up

[RobC]

afternoon to my bx homies. judging by recent posts, it's AFM trouble time for many of us!

recently upon starting up i've been alarmed to be subjected to the car immediately racing up to 3000 rpm at idle, and refusing to come down.

- the throttle position switch is clicking fine and the accelerator cable is not caught on anything
- the idle control valve on the manifold seems to be working ok

to cure the problem i unplug the airflow meter and the car gets very upset, but carries on running at normal (albeit very stuttery) revs (i guess this is the 'emergency' ECU readings kicking in?). then if i turn off the engine, plug the AFM back in, and restart the engine it runs ok. the K light stays on for a while after this, but eventually goes out and the idle is smooth again.

strange or what? i guess it's a problem with the AFM but what? any ideas most appreciated.

[thanuttiscotsman]

hi there rob,
it is not your afm that is cuasing the stay at 300rpm. if you have read some of my recent threads you'll see my car does the same revving up stuff every time i start it. thats the afm not getting clear readings. if your car fly's up to 3000 rpm that is your tps sticking, it prolly doesnt always do it to you. the easy way to stop this is to turn the ign on then push the accelorator down a couple times then take your foot back off it this ensures the connection in the tps is better. try this next time and you will find the car no longer sits at a 3k rpm tickover. my car used to do it a fair bit but now im in the habit of tapping the throttle everytime before i start it and it never does it, mind you i should just change the tb as i have another.

cheers rossco

[jayw]

to cure the problem i unplug the airflow meter and the car gets very upset, but carries on running at normal (albeit very stuttery) revs (i guess this is the 'emergency' ECU readings kicking in?).

If i unplug the AFM with the engine running it dies! Is that not normal?

[thanuttiscotsman]

hi jay,
well it doesnt do that on mine if that helps. mine just starts revving around the place as i assume its trying to get a reading. if your dies then i imadgine whatever it rely's on when it cant get an afm reading is prolly fecked but im not sure what else it gets that info from.

rossco

[RobC]

hi rossco

i already think that my throttle position sensor is fine - because the acc blipping trick you mention (in which i'm well versed...!) is ineffective - hence my saying in the post that the TPS is working ok

so it must be something else...

jayw: don't worry i *think* you're perfectly normal - when my cars running fine, unplugging the AFM also makes it die.

[Anonymous]

Try removing the pipe from the idle valve to the inlet manifold, and block the resultant hole on the inlet manifold. Then start it up. If you can get a reasonable idle by allowing a small amount of air to bleed into manifold (engine warm) through the hole, the I suggest a problem with the idle valve, or wiring, or its piping. Thanks Tobytronicstereophonic.

[thanuttiscotsman]

hi there,
i think toby must be right as its either tps or icv. if its intermittent then prolly wireing prob. i also found previously that only on occasion did the tps not click back to idle. made it look like it was working when i was fooled cos it didnt. i just loosened the acc cable a little to allow more room for switch to close. as for icv's from what ive found in the past re-cons are pretty expensive but im sure someone here will part with one they dont currently need/use.

cheers rossco

[iain a]

.....have you tried the air bleed screw in hole around the back of the throttle?

[tim leech]

K light? I havent got one of them.

[Mike E (uk)]

I once knew of an intermittantly faulty microswitch on the throttle body.
it may click, but that does not mean it is working.
That may well give the symptoms you describe.

A quick check with a Ohmeter should rule this out.

Mike

[jayw]

K light? I havent got one of them.

We don't have them on our early phase 2's. I do have one on the H plate one tho.

Not sure of the reason for the difference, but the same later ones also have the Engine loom connected by a single large connector on the o/s wing by the top mount.

Anyonr know why there's a difference?

[RobC]

i think the k light came along with the ECU change from ML4.1 to M1.3 (in 1991, mid H-plate).

although i used to have an H plate phase 1.5 (i.e. the one with original interior and ECU but later bodystyle) which i swear had a k light, but maybe my memory's going...

[kriskarrera]

My G reg ML4.1 405 has a K light.

[thanuttiscotsman]

hi folks,
you must remember that registrations dont mean much! the orga should tell you more about the age of the car and its systems! ie my car is an h plate but the orga says it sat around for i think 10 months before being registered. oh and its a h plate ml4.1 without k light.

rossco

[kriskarrera]

According to Peugeot the UK mi16 got m1.3 motronic from chassis number 7000000(which was 1991 H reg), I know that's no help to you bx folk but I assume Citroen started on 1.3 around the same time.