Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[wingman]

Having now spent all day replacing the emission control valve on my 3.2 DBW mig (what a barsteward of a job!! Plenum off - Scuttle off and tore hands to ribbons) I have now gone back to an original problem that I had after the car was converted to LPG when I was getting 0441, and fuel trim codes on (both banks) which made me suspect purge valve was faulty or leak in vent pipe to valve.
On LPG or petrol (doesn't matter which) the idling speed will gradually increase to about 1500 - 2000 rpm when the engine is hot and the auto box is in N or P. (when in drive will revert to normal ie 600-650 rpm). When this happens a click can be heard from something at the rear of the engine. Blipping the throttle will sometimes revert back to normal idle which will then gradually increase again. Have had plenum off twice to check for air leaks, checked all plugs and vacuum pipes are connected and have blocked off the purge valve breather port to check that for air leak as well - all to no avail. Cannot see what I could have disturbed to make this happen. Car has been running/idling fine on LPG and petrol for last 4 months with purge valve breather port sealed off while waiting for purge valve to be changed. No codes stored - Help please!!!!!!

[Marks DTM Calib]

Well high idle must be an air leak.

So check all the breathers are ok and conencted correctly (no gearbox breather connected up by mistake for example)

[wingman]

OK will check tomorrow but am pretty sure that the gearbox breather is not connected. Just to check there are two large pipes which go to the outer breather connect stubs, one small tube from crankase breather adjacent to other end of large split pipe and lastly one from purge valve. Is that right??

[wingman]

Have now rechecked all breather pipes are connected and are in right place on breather box (auto box vent is not connected) and all pipes seem airtight (ie no splits/holes etc). Cannot hear any sound of air leak from around plenum but idling speed still climbs to 1500 - 2000 rpm gradually whether on LPG or petrol. Have again looked over all work carried out yesterday but cannot see anything wrong. No codes stored. Anybody any ideas before I give up and have to go to stealers.

[wingman]

Still struggling with this - anyone???

[Kevin Wood]

Does the idling still return to normal when the purge valve feed from the plastic breather bridge is blocked off?

Other possibilities are a loose or split brake servo hose (did you remember to tighten the union onthe plenum?) or an "O"ring under the plenum that has gone adrift as you replaced the plenum.

Kevin

[RobG]

Have you tried spraying carb cleaner around area of plenum and vac pipes. with engine running. If engine sound/revs change you will have found an air leak :question

[wingman]

Kev/RobG
Thanks for replies - Kev I did try blocking the purge valve breather yesterday but didn't seem to have any effect this time (unlike before) but will try again. If this is causing the problem will the fuel trims which would be all over the place as they try to correct the mixture take a little while to recover or will they instantly come right. I will recheck the servo union on the plenum but this was my first suspect that I checked and seemed fine.
RobG - I will try spraying around the plenum but will have to do this when engine is cold and not revving at 1500 - 2000 rpm as any note change is hard to tell then.

[wingman]

Kev  - sorry forgot to say that also have checked O rings were not displaced and when put back second time greased them to keep in place

[Marks DTM Calib]

Consider that to get high idle revs on a drive by wire throttle setup there must be one of 2 things

1) An air leak

2) The throttle butterflies are not abe to regulate the idle properly.

So it may be worthwhile removing the throttle body assembly and cleaning the throttle butterflies.

[ians]

I seem to recall when I removed my 3.2 plenum that there was a vacuum pipe attaching underneath the front of the plenum  - probably onto the throttle body itself - can't exactly recall - but it struck me that it would be easy to dislodge and not be easily visible with the plenum in situ..

[Marks DTM Calib]

I seem to recall when I removed my 3.2 plenum that there was a vacuum pipe attaching underneath the front of the plenum  - probably onto the throttle body itself - can't exactly recall - but it struck me that it would be easy to dislodge and not be easily visible with the plenum in situ..

Correct, from the pre throttle side though so wont affect idle. It connects to the injector rail pressure relief valve

[wingman]

OK have blocked off purge valve breather again and have checked servo pipe/union for leaks and sprayed carb cleaner liberally around plenum and pipes. Carb cleaner seemed to have no effect on engine revs so would seem that there are no airleaks around plenum. I seem to recall that when I originally had this problem and suspected the purge valve and blanked off the breather that it did not immediately cure the problem then but seemed to settle down after a while. Could this be as the trims correct themselves?
MarksDTM - yes I will have a look at that but will see if action above has any effect first. However not sure exactly where the butterflys you mean are. Looking into the front of the throttle body there are two large butterfly flaps but I thought these were operated by the vacuum pipe underneath and were the front air ram butterflys or are they what you mean and are connected to the small servo motor on the left of ther body which presumably is driven from the position of the accelerator pedal. These can be pushed open slightly and seem to snap back into position OK. Are there other butterflys behind these or have I got it completely wrong!!

The reason I am panicking about this is that MOT is due on 23rd and I am not sure whether a blocked off breather and/or a high idle would be a failure on emissions checks.

Kevin - will PM you on a separate but related matter to do with LPG calibration

[wingman]

Thanks to Kevin and Marks DTM I eventually found out what was causing idling to hunt. When removing old purge valve vacuum pipe had been dislodged from brake servo pipe T piece causing idling to hunt between 1000 - 2500 when hot on petrol (higher on LPG?)and lumpy when cold. Reconnected and now seems back to normal but took a few days to settle down for some reason. Moral is check everything after disturbing apparently unrelated parts. As a bonus passed its MOT today. Thanks guys, this forum is invaluable to all mig owners!!