lumpy idle?

[clubman_dan]

ok ok, my car may be perfect, but its still a 480 with 95k so it aint totally perfect!
seriously though, the only issue i have noticed is that the idle is quite lumpy, it sits nicely at about 800 rpm and is rock steady, but it feels very lumpy!
also when coming to a stop, (i.e in neutral or clutch dipped) idle will drop to about 400-500rpm and come back up to a steady 800rpm. where it will stay solid but be lumpy. it never stalls
it also feels lumpy when accelerating from a low speed (e.g from 30 in 4th gear or 40mph in 5th) i am sure these two things are linked!

so far i have:
-checked resistance at the maf, it is 380 ohms
-i have soaked the idle control valve in meths overnight and cleaned it as best i can, then lubricated it. however the problem still remains.
-i have checked resistance across pins 1 and 3 of the idle valve, it was 40ohms which i believe is acceptable?
-i have reset the ecu, this has not made any difference
- i have unplugged the idle control valve, the idle initiall remained unchanged but felt marginally less lumpy, but after blipping the throttle, fell to about 500 rpm, still smooth. is that normal??

i am running out of ideas now, i don't want to go blindly messing about too much as this caar is really too nice to screw up so i am considering taking it to a garage, i wonder if there is anything i have missed which is simple to check?
its not much of an issue, its just a bit irritating you know what i mean!
cheers in advance
DAN

[hjkort]

clean the idle valve properly.

[clubman_dan]

how do you mean? do you think i need something like carb cleaner rather than meths?
cheers
DAN

[clubman_dan]

any other opinions?

[JohnTurbo]

Back in the days of yore the idle valve was victimised for being the source of most idle issues. I'd say this was largely misplaced hatred. If you're called "Mr Homicide" you'd expect suspiction from the neighbours!

Your problem sounds more synonomous with a small air leak...possibly one of the small tubes to the EVAP system from the throttle plate, a bad gasket or a leaking oil rebreather.

I set fire to a small roll of paper and waved it, smoldering, round the engine when running to find my airleaks. Insert disclaimer here.
Beter was to pressurise the whole intake using an old tyre valve, jam jar lid and air compressor, but i reallise most ppl don't have one of those.

Intercooler could also leak.

Assuming your leads/coil/dissy are all ok, that only leaves the flywheel position sensor and airleaks.

[stu chacks]

I set fire to a small roll of paper and waved it, smoldering, round the engine when running to find my airleaks.

Also a great way to check if the fuel injection system has any leaks eh JT!

Stu.

[clubman_dan]

would a jam jar lid, trye valve and a small electric tyre pump be able to do the job (obviously a lot slower!)
i assume, you remove the MAF and jubilee the jam jar lid in that pipe then just pressurise it and listen for air escaping?
i took the idle valve out again this evening, soaked it good and proper in some really evil smelling, injector cleaning stuff. i managed to get some dirty shite out of it, but refiting made no difference at all.
so i guess that your right johnturbo, that poor old idle valve just gets the stick for anything!
cheers
DAN

[JohnTurbo]

Dan, i was blowing air in at 5 bar and it was still tough to find the leaks...so unlikely the pump job'd work. You'd maybe manage better with a decent bike pump actually!

[heavend]

It's not something routine like spark plugs, leads, distributor cap or rotor arm? When were these last replaced? And are the plugs of the correct temperature range and gap?

I think the idle control valve is often blamed. The resistance you quote is OK - provided the rotor is free to move, that beasties OK.

A leak in one of the air/vaccuum lines is possible. Old rubber perishes and cracks, and gives rise to problems you just don't see in newer cars.

My 16v 940 had an annoying intermittant idle problem - turned out to be carbon build up in the combustion chamber causing sticking valves and sooty plugs. Running a combustion chamber cleaner through sorted the carbon build up there, and correct plugs prevented recurrance.

[clubman_dan]

it must be a leak, the boost guage will usually sit at -14psi at idle, however it will fairly regularly float upwards slightly, and drop again. sometimes as much as quarter of the way back up to atmospheric pressure.
now i just need to find the bloody leak! i have checked the little hoses behind the butterfly, going to the dumpvalve etc. i need to check the ones on the other side of the plenum now!

[rapid R5]

Try squirting some brake cleaner, or any other flammable liquid on your intake hoses, if it sucks it in the engine burns it and you can hear the difference.

steve

[clubman_dan]

well i cant seem to find any leaks! my dump valve is still attached with the original clips, and i have also noticed that when i lift off the throttle, it sounds a bit like someone blowing into a bottle. (it doesn't sound right!)
is there any chance a knackered dump valve would cause the problems i have been getting?
also my car cut out this evening, as you accelerated, it would just stop! almost make your head hit the steering wheel! it was like the ecu was cutting everything! i turned the car off and on again and it stopped?! any ideas what could cause that ?!?
cheers
DAN

[guitarcarfanatic]

Thats the ECU hitting safe mode. Was it boosting abnormally high? Some times happens when there is a broken pipe from the boost solenoid(cant's remember which pipe but there are only 3 it could be!) but that ios usually complimented by boost off the scale. Maybe check all the boost solenoid pipes as a break or split may be the cause.

With regard to the lumpy idle, I couldnt see the DV being the problem unless perhaps it has completely died and is stuck open or something. Normally they just lose their springyness so creep open when boosting but it it is proper knackered it might be stuck open constantly causing the car to loose air through the leak...thinking about this though the air would just be leaking back into just before the turbo and therefore it would already be seen by the maf so shouldnt affect the mixture and cause a problem. My money is on a leak. Maybe the intercooler? I think the best way is to take it off and then clamp one hand over one hole and blow in the other. Ylou shouldnt be able to blow. If you are it's leaking! Only takes about 10-15 minutes to bet off though so not too difficult!!!

[clubman_dan]

it wasn't boosting abnormally high at all! it was pretty random really! i don't know if it was just a one off or something. i will keep an eye on that. it seems to hold boost fine, so i am not sure about leaky intercooler. it boosts to the end of the yellow right through the range. i am going to double check alll the vacuum pipes i think and make sure i havent missed anything.

[clubman_dan]

rechecked the pipes, all seem fine, one of the three pipes on the left of the plenum, felt a bit loose, so i removed it an put a jubilee clip in place of the original one, that made no difference..
i really don't want to take it to a garage and suffer the wallet crippling i am likely to recieve but i fear it may be the only way to fix this! there is only so much i can describe via the forum!
the only other thing i thought was a bit odd is the gold disc attached to the inlet for the servo, (one way valve?)
if you feel it while the engine is running you can feel a ticking inside it, as if the valve is opening and closing repeatedly! i have no idea if this is normal coming from a mini background where i made do with non servo assisted drums
i hope i can work this out.
or its off to the garge
sound like its possible?
DAN
p.s cheers for all the help guys, i don't know what i would do with out it!

[clubman_dan]

idle seems to be improved slightly now! pretty random, its still terrible when the engine is cold but once its warm it doesn't seem to bad really. if the heater is on full blast or if you switch on the a/c though it really gets rough!
the juddering remains though, when you accelerate in 4th and 5th gear (doesn't seem to do it in any other!) it really shudders, i thought maybe it was wheel balance but it stops if you lift off, it feels like when you pull away in the wrong gear and the engine judders.
i was thinking if the fuel filter may be a possibility?
cheers
DAN

[clubman_dan]

i have decided to ressurect this thread, my car is still very lumpy at idle and its annoying me now, so its time to fix it!
i am convinced that its due to a leak somewhere, the pressure guage will not sit at -14 on the gauge, it hovers above it, if you lightly touch the throttle it will drop to -14 though. the idle speed is rocksteady at around 800-900 rpm it doesn't move, it is just very lumpy at idle.
the car runs fine throughout the range otherwise and it boosts cleanly to the end of the yellow. the only other thing of note is that when coming up to a stop, and the clutch is dipped, the revs will fall to about 300rpm for a split second before rising to 800-900and staying steady.

i have managed to put up with it for a while now, but its getting annoying and i want to fix it.
has anyone else had a similar problem? any advise?
cheers
Dan
p.s i have changed the spark plugs, replaced the recirc valve (the old one turned out to be fine anyway ) and the idle valve has been cleaned and tested.

[martinholmesuk]

What idle valve you have? T or L shaped?

Want to borrow one of my spares?

[clubman_dan]

its a t shape idle control valve, i am not too sure if it is the problem though. i have cleaned it out and tested the resistance on it, and it tested ok.

[clubman_dan]

ressurectioin! (again)
i think i may have cracked it!
i was looking at the idle control valve today, and i noticed that the wiring plug looked twisted, as though it was on upside down. its always been like that so i never really thought about it.
but today i thought i would try flipping the idle control valve the other way up which meant the plug went on straight with no twists in the wiring.
started the car up. and hey presto! idles smoother than before, and it doesn't drop the revs everytime you come to a stop, it now holds at about 1100 rpm for a split secoind before falling to 800 and staying steady.
I hope this is the end of the problem, it has been doing my head in!