I've cross posted this from the 328 section to broaden the request for help Original Post Car is an 88.5 Euro non cat car and it's just recently developed a fault where the idle surges and drops between 500RPM and 900RPM continuously, settling a bit but not completely after 30 seconds or so, it's very much more noticable after about 5 to 10 minutes running from cold and as it gets hot it is much better, there is a very slight variation detectable when hot but that could be normal. I've cleaned up the coils,amps, distie caps, leads and extenders, greased the throttle linkage and generally checked all connections are tight. It also smells a bit rich? ------------------------------------------------------------------------------------------------------------------- Follow Up Post Well I thought I'd made progress but I'm getting intermittent results. The problem, when cold I'm getting no warm up cycle ie it tries to idle at around 500rpm not 1500, as it warms the idle slowly increase and if you drive the car you get a situation where the idle revs will drop to 500 when coming to a stop and the idle surges and falls between around 500 and 900 then eventually settles to 900, car during all this smells like it is running rich, once warm it idles OK at around 950rpm although there is still a slightly detectable rise and fall in rpm perhaps only 75 or so, the car also seems to be down on power and there is also a detectable misfire particularly it seems around 5,500rpm So far I have Set idle with piece of paper and air jet as advised on here Checked AAV in Freezer and Oven and it works to spec Checked there is 12v to AAV Replaced all vacuum hoses and clips Checked for vacuum leaks with carb cleaner and WD40 (none found) Cleaned all connectors Stripped and cleaned Throttle body Checked 12v at WUR Checked and Cleaned ECU earth Hot HC was checked at MOT last Week and was just slightly high, specialist advised not worth adjusting Yesterday I was trying to find the problem just after start up and wiggled (technical term ) the WUR and the revs shot up to around 1400 stable, it then over time dropped to the correct 950 idle. I drove the car 70 Miles over 2 journeys and it behaved impeccably. The connections to the WUR were very corroded and I cleaned these up So I thought I'd found the problem with the WUR not heating up due to poor connections but this morning the problem is the same only wiggling the WUR makes no difference. Am I right to suspect he WUR?, if so I'll get it rebuilt Thanks, all contributions gratefully received
Mark, as you know I had the exact same symptoms & it turned out to be a hole in the vac hose that goes back to the ignition module in the boot. However, based on what you have said I would suspect the WUR because I can't see what else it can be. The only thing that rings a bell is that it seems to be running a bit rich - which is what my car was like & that points towards an air leak What I had was that with a small air leak in the warm up system/vaccum hoses/ manifold or plenum gaskets or seals then at idle you need to fatten the mixure up to get the CO right. You then manage the revs down with the air bleed/idle screw - so it would appear to idle correctly when hot. But if you do this you then have the throttle body/air screw closed down so far such that the thing won't idle properly when cold and you get the hunting thing you described. Also further up the rev range the air leak becomes pretty irrelevant (because there is so much air coming in the intake) & so means the mixture is then too rich (because you have adjusted it to cope with the extra air coming in at idle). As I found out, the system just will not work unless its sealed & you end up compensating with the mixture which shows the right kind of CO level at idle but that same adjustment then means its running too rich at higher engine speeds. The only other thing (and I'm not sure why it might be an issue!) is have you checked that big spring loaded plate thing (just after the air filter) is lining up properly? I seem to remember reading somewhere that it can screw things up if its not dead level. Maybe give Phil at QV a call & see if he has a spare WUR on the shelf you could try. I.
Mark, Based on your description...and if the car were in my shop, the very first thing I would check would be the cold and hot control pressures, as I believe that the problem does indeed point to the warm-up regulator. Regards, David
Thanks Iain, David I checked the plate and it appears to be level, I've cleaned up the area to ensure no grime has got in there. I'll go searching for vacuum leaks again although I'd pretty much eliminated the pipes by disconnecting/ blocking off. I'm struggling to understand the relevance but it has only misbehaved since I collected it from it's bare metal respray?
Too much Welsh air mate !! Maybe ask Al if he disconnected anything - but I can't see why he would have. A leak round the plenum/inlet manifold would do it. Have you checked that the vacuum advance on the digiplex is OK? AFAIK there is a membrane inside the box. If that was torn then the thing would just be sucking air up the vacuum tube (much the same as mine was effectively although mine was caused by a hole/gash in the tube). More of a problem though would be you'd have no VA higher up the rev range. I read somewhere recently about someone with a knackered VA membrane in the ignition box. Disconnect the tube from the plenum & suck on it gently & make sure air is not coming in that way.
