High Idle

[davemar 16]

Mi16 1.9 engine running on 8v Jetronic ECU with dizzy adapter,etc.

 

I've recently had to do some big jobs on the engine (HG replacement, etc), and have finally got close to getting running properly - ready for it's MOT. There's been a few problems along the way, but have solved them, the most recent was finding a poor earth connection on the ignition module which caused it to stop firing at certain times (a problem but less so before the current work was done).

 

The last (hopefully!) problem is that the idle is sitting around 2000rpm, even when warmed up. I occasionally used to suffer a sticky throttle which caused this, but I've given it a good clean and even grabbing the throttle spindle by hand to ensure it is 'shut' it still hums away at 2k. I've tried adjusting the throttle end-stop screw, but even that doesn't help. I measured the temperature sensor resistance when cold, and it measure about 6kohms, so that's not gone open-circuit. Maybe it is worth checking the voltage across the sensor while the engine is running and warm (anyone know what voltage to expect)?

 

The engine used to idle pretty nicely at around 900-1000rpm before I did all this work, so I'm not sure what else can be causing it?

[yeti-dj 7]

Hello, i recently serviced a friends car and it idled high after and it was due to an air leak at the inlet manifold due to me not refitting a bolt, oops..

 

hope this helps...

Edited January 6, 2008 by yeti-dj

[davemar 16]

Hello, i recently serviced a friends car and it idled high after and it was due to an air leak at the inlet manifold due to me not refitting a bolt, oops..

 

hope this helps...

All the bolts are present and tight, so you haven't been near it!

There weren't any obvious signs of an air leak, but I'll certainly check over again.

I did squeeze the hose feeding the SAD in case that was jammed open, but that made no difference.

[davemar 16]

I had a good check round for air leaks, and certainly couldn't hear anything - though they are quite loud engines so listening for air leaks isn't easy. I removed the throttle housing, AFM and related connecting bits and checked those over and everything seemed fine. I nipped up the inlet manifold nuts/bolts, and tried to inspect the injectors in the manifold if they were blowing, but they all seemed fine. So there doesn't appear to be any air leaks.

 

I couldn't measure the coolant temperature sensor voltage, but when I disconnected it the revs plummeted to stall it; so it's doing something right - whether it is producing the right resistance I can't confirm. I can't see a simple sensor like this being slightly out, it either works or it doesn't?

 

I then tried adjusting the AFM idle screw, but that made no difference. I tried adjusting the coil spring tension in the AFM which can usually tweak the idle a bit when adjusting the mixture, and I did managed to get it to drop to around 1500rpm, but it was running very rough and clearly not the right mixture.

 

Could the fact that I've had the head skimmed and am now running a slightly higher CR have any affect? Would I need to adjust the ignition timing?

 

An hour or so into my faffing around on the engine and having it running several times, it decided to cut out and not give a spark, with the LT side of the coil not having a signal. I thought I cleared this problem up a couple of days ago which was a dodgy earth which I fixed. The earth was now fine, and it restarted again after a few minutes without me doing anything or being able to track the cause down. Very frustrating!! Maybe the new ignition module is a bit flakey?

[yeti-dj 7]

Well at least you now know that all the bolts are there..haha

 

Guessing that you have checked that the throttle position sensor isnt holding the throttle partly open?

 

have seen this before the idel screw was adjusted so much that you didnt notice it.

 

Hope this is more help than my bolt theory...

 

good luck....

[davemar 16]

The throttle snapped totally shut when released, so no air getting through there. The throttle switch also clicked when should too.

[davemar 16]

Just another thought: I've fitted a new exhaust manifold that's a slightly different shape to the old one (and is free of cracks too!), could that affect the idle, or the ignition timing requirements?

[lee-bg 0]

As i understand, you are running mi16 engine on 8v ECU and still using the SAD device from the 8v engine ? Is that correct? How did u connect the SAD to the inlet manifold where the usual IDLE valve for 16V sits ?

i tried doing this in the past, but was unable to achieve proper idle speed. So i just installed a "bolt" which lets small amount of air in and keeps idle always at 1100 rpms...

also, please tell me from what 8v engine is the ECU and AFM ? That may also affect things.

 

ops. i guess i didnt read all your post As you wrote in first message. have to check my files at home how it was for Jetronic. I think idle was controlled by the AFM screw ? not by ECU as on later cars.

 

 

Regads

Edited January 9, 2008 by lee-bg

[kyepan 291]

check that the diaphram in the vacume advance (looks like a bicycle bell) on the back of the distributor has not perforated, as that would lead to an air leak and affect idle.

 

to check take the hose off the other end, leaving the one on the dizzy in place and suck on it.. air should not come out.

 

cheers

 

J

[davemar 16]

As i understand, you are running mi16 engine on 8v ECU and still using the SAD device from the 8v engine ? Is that correct? How did u connect the SAD to the inlet manifold where the usual IDLE valve for 16V sits ?

i tried doing this in the past, but was unable to achieve proper idle speed. So i just installed a "bolt" which lets small amount of air in and keeps idle always at 1100 rpms...

also, please tell me from what 8v engine is the ECU and AFM ? That may also affect things.

 

ops. i guess i didnt read all your post As you wrote in first message. have to check my files at home how it was for Jetronic. I think idle was controlled by the AFM screw ? not by ECU as on later cars.

Regads

Yes, I'm using the SAD from the 8v engine which connects between the duct between the AFM and throttle and the inlet manifold connection.

It's exactly as it was before when it idled correctly.

I also tried squeezing the hose into the SAD to block it off, but that made no difference.

[davemar 16]

check that the diaphram in the vacume advance (looks like a bicycle bell) on the back of the distributor has not perforated, as that would lead to an air leak and affect idle.

 

Good point, I hadn't checked that. I was running out of ideas of where possible leaks could be. Let's hope its that.

 

I did try adjusting the ignition timing to see if that altered things. I could get the idle to drop, but it was more retarded than Jade Goody, and clearly not going run well in that situation (even a throttle blip became laboured).

 

I also stuck a vacuum gauge on there to see if that revealed anything. It sat pretty steady in the 'good' region, so nothing out of the ordinary there.

 

I had noticed when I start the engine it does splutter a little to get going (but it's always been a bit like that), but the idle does seem to start off quite low. It's only when the throttle is blipped does it fail to settle back down to 900-1000rpm and drops only to 2000ish rpm instead. But the throttle isn't sticking, as I'm doing this by hand at the engine and forcing it shut.

[davemar 16]

Good point, I hadn't checked that. I was running out of ideas of where possible leaks could be. Let's hope its that.

Come to think of it, I did remove the vacuum pipe and block it off on the manifold to eliminate that potential leak (as a test), and it made no difference, so it appears the diaphram is probably OK.

[davemar 16]

I've decided to remove all the inlet manifold stuff, and ignition gubbins too and give everything a good going over with the hope that refitting it all will fix it.

 

I decide to pour some water into the inlet manifold with the throttle attached to see if anything leaked out, and all I got was a tiny dribble past the throttle plates, but you would expect that (it was holding back a couple of litres of water).

 

I've also decided to replace the injectors as I have a spare set which look in good nick.

 

Let's hope something shows up or just magically gets fixed in the process....

[davemar 16]

OK, I took all the inlet manifold stuff off, ignition system, injectors and so on; then refitted it all (with different ignition amp and coil), giving it all a good check over. Starter her up and once the engine got a bit of warmth into it, it still idled way too high.

 

I'm now beginning to suspect the valve timing might be dodgy. Could the tension of the cambelt affect the valve timing enough to cause idle problems? I did notice another thread where someone had a 1500rpm which turned out to be a cam timing issue, so I'm beginning to think that. Seeing as I replaced the cambelt as part of the head-gasket replacement it is possible. I did triple-check the cams and crank were all lined up with the various locking holes, but maybe a lop-sided tension could knock things out.

 

Another reason to suspect is that when it starts up the idle is nearly sensible (1200-1300rpm). But when I rev it, and let it settle again the idle only drops back to 2000rpm-ish. I'm thinking the tension on the front run of the cambelt transfers to the back run (one is tighter and one is looser), thus altering the valve timing and changing idle.

 

Would a 0.010" head skim cause this cambelt tensioning problem? I found the long front run of the belt required the tensioner to be in the position you would expect to cause the maximum tension but still gave an easy 90 deg twist. I would expect the tensioner to have enough variation in adjustment to make it a lot tighter than that at it's maximum?

 

Does this sound like a feasible diagnosis?

[davemar 16]

Yet another reply to myself....

 

I refitted the cambelt as I felt it wasn't tensioned correctly as it seemed to flap a bit too much on the long run. It certainly looked and sounded better after refitting it, but it didn't sort the idle problem.

 

I measured the voltage across the coolant temperature sensor, and it gradually dropped as the engine warmed, finally sitting around 1.6v when the fan kicked in. This I assume is normal.

 

I then decided to reconsider the air-leak possibility again, so I removed the air filter (K&N induction unit on the end of the AFM) and while the engine was running I block off the inlet by putting the palm of my hand over it. The revs dropped, but the engine didn't stall. Would you expect it to stall with the inlet blocked off. Certainly I could see the duct between the AFM and throttle body contract when I did this.

 

So the engine still idles anywhere between 1500 and 2500 rpm (usually higher after I given it some revs), and I'm running out of patience here! Any ideas anyone?!!

[Mikey S 29 1 Cars]

I then decided to reconsider the air-leak possibility again, so I removed the air filter (K&N induction unit on the end of the AFM) and while the engine was running I block off the inlet by putting the palm of my hand over it. The revs dropped, but the engine didn't stall. Would you expect it to stall with the inlet blocked off. Certainly I could see the duct between the AFM and throttle body contract when I did this.

 

So the engine still idles anywhere between 1500 and 2500 rpm (usually higher after I given it some revs), and I'm running out of patience here! Any ideas anyone?!!

 

 

i would definately go over the airleak again, it should stall when you block the airfilter. have you tried blocking the air inlet and listening for leaks while it is blocked off. i should imagine if it had an airleak this method would show it up very vividly. i sometimes tend to use wd40 when checking for airleaks. a squirt around pipes, inlet manifolds etc then a sniff of the exhaust can usually give you an pretty accurate way of finding them as it smells funny when its been burnt.

 

have you thought about changing over to motronic?

 

hth

 

mike

[davemar 16]

i would definately go over the airleak again, it should stall when you block the airfilter. have you tried blocking the air inlet and listening for leaks while it is blocked off. i should imagine if it had an airleak this method would show it up very vividly. i sometimes tend to use wd40 when checking for airleaks. a squirt around pipes, inlet manifolds etc then a sniff of the exhaust can usually give you an pretty accurate way of finding them as it smells funny when its been burnt.

I'll have to disconnect the alternator to do this as the sound of it spinning and the breeze it's vanes give off hide any potential air leak type noises. I might aim to gradually block off various parts too. I'll certainly try those things though.

have you thought about changing over to motronic?

I have considered it, and do have some of the gear, including the flywheel having the teeth on it. But I'm keen to get the thing through its MOT and back on the road ASAP, as it's currently stuck 30 miles away from home in a garage I'm renting. Once it's at my home I'm going to start preparing for a Motronic upgrade. Given that my 'back-up' car is off the road too at the moment I'm just desperate to get car that works!

[pug_ham 242 3 Cars]

A simple one for you, have you tried turning the idle speed screw in to bring the idle speed down to a sensible level?

 

If not give it a try to see how it drives & idles then.

 

The vacuum advance shouldn't be connected afaik even when running on injection because the 8v dizzy advance is all wrong for a 16v engine so you can safely block it off imo.

 

Check the routing of your throttle cable to the TB, I've seen these routed badly & catch occasionally so the idl stays high randomly.

 

Graham.

[yeti-dj 7]

I know it will sound daft but do you have the wiring to the temp sensor/temp guage the right way round?

 

seem to remember having a problem ages ago and this was the problem

 

The sensor on mine was also goosed and gave some very funny idling now and again.

 

Thats the good thing about the motronic set up with the ICV, since fitting the correct set up to my mi16 205 the idle is always rock solid, freezing cold or boiling hot and it gets rid of the kangaroo petrol and well

 

Good luck..

[davemar 16]

I know it will sound daft but do you have the wiring to the temp sensor/temp guage the right way round?

The temp sensor is a two pin jobby with a "junior timer" connector, and the temp gauge is a single pin job with a spade connector; so it's pretty difficult to swap them I think. Even so, I ought to give the wiring to the ECU the once over in case something has awry.

[davemar 16]

A simple one for you, have you tried turning the idle speed screw in to bring the idle speed down to a sensible level?

 

If not give it a try to see how it drives & idles then.

 

The vacuum advance shouldn't be connected afaik even when running on injection because the 8v dizzy advance is all wrong for a 16v engine so you can safely block it off imo.

 

Check the routing of your throttle cable to the TB, I've seen these routed badly & catch occasionally so the idl stays high randomly.

 

Graham.

I tried the idle speed screw to its limits, but no joy. Also as thing hasn't got an MOT, driving consists of 10 metres of driveway at the moment!

 

I hadn't realised the vacuum advance should be disconnected for the 16v engine, I'll certainly give it go once things are sorted. I'm sure the hose dropped off occasionally over the years without a huge change to the performance, so it makes sense.

 

The throttle cable did used to occasionally catch, so I fixed that. A quick hard blip often solved it while driving and woke a few old dears up too.

[davemar 16]

I had a bit more of a rummage around last night and disconnected the alternator so I could listen for air leaks. Again I removed the air filter so I could block off the inlet and listen for leaks, and sure enough I could hear one! There was some hissing coming from the throttle body, right out of the spindle which the cable attaches to. This might explain why the idle seemed to settle differently after the engine was revved, so the spindle moved slightly making the air leak a different size.

 

I decided to take apart the throttle body to inspect it further, and the rubber seals in the spindle bearings holes were pretty grotty, and there was quite a bit of play in the holes. I'll probably have to replace the throttle body, but at least it sounds like the cause of my problems!

 

On the downside, the ignition system decided to be on the blob again and failed to fire on one occasion when starting. I've tried swapping both coil and ignition module (all combinations I'm sure), but there's just this occasional non-working. Maybe a dodgy connection somewhere, but it's proved tough to track down.

[James_m 0]

Have you checked the core plug type things on the end of the manifold? Maybe the manifold itself is cracked somewhere leaking air?

Ive never seen an Mi running on an 8v TB, but surely with the throttle shut and the adjustment screw wound down as closed as possible there is not enough air for 1500rpm?

You have you got your oil filler cap on with all the breathers plumbed in?

 

Edit - too late! At least you've finally sorted it by the sound of things!

Edited January 16, 2008 by James_m

[davemar 16]

Have you checked the core plug type things on the end of the manifold? Maybe the manifold itself is cracked somewhere leaking air?

Ive never seen an Mi running on an 8v TB, but surely with the throttle shut and the adjustment screw wound down as closed as possible there is not enough air for 1500rpm?

You have you got your oil filler cap on with all the breathers plumbed in?

 

Edit - too late! At least you've finally sorted it by the sound of things!

I'll let you all know if a replacement TB sorts it out.

 

BTW, it's the Mi16 throttle body, not the 8v unit. Still looks buggered though!

[jim205GTI 3]

Going by previous posts on here the spindles on the mi throttle body are prone to wearing

suprised no one thought of it before

good thats it seems to be sorted though!!