Technical Still not luck to get the idle to work properly

[dumbledore]

Trying to fix an idle issue on my car for while now with no luck. Played around with replacing the stepper motor and the throttle potentiometer wih no effect. The idle is consistent high at around 1.3K. Only occasionally it drops below 1K but then it goes back to 1.3K. There is a stop on the throttle body that can be adjusted to control the closing possition of the throttle. Is there a point playing with this to try to sort the idle?

 

[fingers99]

No. Unless some twerp has played with it before.

Chances are, you have an air leak.

 

[blu73]

has the throttle body been off? high idle is nearly always a vac leak somewhere..

but does pulling the vac line off the map sensor while running make it run different, better or worse - it should make a difference basically one way or another.

Is the TB nice and clean?

If you suspect something on the TB you could just go get a couple from scrappies, only £5 a pop at my local yard and try swapping the whole thing over.

 

[dumbledore]

Cheers,
I have looked to check for any leaks but seen none. I have removed the vac sensor line in the past and usually it made thing worse. One thing I tried is remove the small vacuum line that goes from to back of the throttle body to the top plastic cover where the main rocker cover breather pipe fits. When removed, at idle this line sucks in air. If I block the air getting in, the idle goes down.

I never removed the throttle body. I removed it togetther with the inlet manifold to replace the head gasket i nthe past, so the inlet manifold gasket I assume is also OK. Not to keen to remove the throttle body as there are quite a bit of pipes to be disconnected and put back on. I did get a throttle body the other day though but it was the wrong one from an automatic car.

Any tips to confirn a possible vacuum leak will be nice to hear from you.

My next step is to sort the exhaust as the rear box appears to be internally damaged. I also have an O2 sensor that I want to fit.

 

[fingers99]

Get some small bore tubing, -- like windscreen washer tubing, listen for a hiss. There's a diagram of where the hoses go on the TB in the cinq/sei guides.

Take nothing for granted -- usually the inlet manifold gaskets -- they're cheap enough, anyway -- can be re-used with sealant. Without, they'd be suspect.

 

[dumbledore]

OK today, I went and replaced the exhaust from the CAT (one piece) and also replaced the O2 sensor. The effect was smaller exhaust noise but idle still bad. I decided to have another look at the vacuum lines. Did not see anything again, but decided to replace the steper idle motor with the one from my spare throttle body. Initially it started hunting, then the revs shot up to 4K, at which point I stopped the engine. I then restarted the engine and things started improving. I managed to see the idle to go down to 1K and stay there for longer. I will need to test this more.
However, my main problem is that the exhaust has not fixed the vibrations in the engine that I have noticed since my recent clutch replacement. The vibration is definetelly not right as it already caused one of my downpipe bolts to come loose.
I am going to re-adjust the rear engine mount and move it to some other position and see if that has any effect. DO you think this is a good idea?

 

[fingers99]

One of the mounts might be an issue, but usually the rear one will produce a pronounced clunk if nackered.

Idle should be 850 or so, so I still suspect an air leak (or maybe an overtight throttle cable -- there should be discernable slack in it).

 

[dumbledore]

Cheers, I will need to do some more testing with the idle. The cable is not tight as the battefly control rod leaver is sitting on the stop. This is why I was tempted to adjust the stop.

The vibration is my main worry though at the moment which I need sort out. I can leave with the vibration but not happy the nuts and bolts come loose in time as a result of the engine vibrating more then it should.

 

[dumbledore]

Update, OK idle seem to hold up OK. Although is not getting below 1K, the idle is steady and there is no hunting. However, engine vibration and higher then normal exhaust noise is still somthing that I cannot explain. I replaced the exhaust from the cat back, I inspected the CAT and looked at the downpipe that looked OK. However the flexi side of the downpipe cannot be inspected properly as there is a mesh above it. As I run out of ideas I am suspecting that the flexi side may have started to deteriorate, and hence the higher exhaust noise then normal. Any ideas how I can diagnose the flexi.

 

[blu73]

its cheap and easy to replace if you suspect it. leaky exhaust can sometimes result in funny running and poor emissions, particularly if its leaking near the lambda sensor for example.

 

[dumbledore]

its cheap and easy to replace if you suspect it. leaky exhaust can sometimes result in funny running and poor emissions, particularly if its leaking near the lambda sensor for example.

Did not replace this, but done the following test: Started the engine, went to the side of the car and from there grabbed the exhaust and tried to pull it forward and backward. Could not hear any change in exhaust noise so assume the flexi downpipe must be OK.

I still don't know the cause of the extra noise and vibration. I assume the new engine mount is too stiff while the others are still tired originals. Some sort of inbalance in the mounting can have caused this? Looked around and appart of the mount that I managed to get, the other 2 don't seem to be available from the usual shops, ebay, etc.

The idle though is now still behaving. I can see 900 rpm now with all electrics on. However, when I switch off the lights the idle goes back to 1K. So from my experience, I can assume that the idle stepper motor was the likely culprit. Before this fix the idle would do 1K but will not be able to stay there for more then 10seconds and then will hunt to about 1.3K. Occasionally going back down to 1K and then again hunt up.

 

[dumbledore]

Decided to give my car the MOT test and am happy it passed. So the vibration and noise can't be that bad.

The emission test was better then my last MOT.
Idle Speed: 995, CO=0.27%.
Fast Idle: 2815, CO=0.11%, HC=31ppm, Lammda=1.012

Also looked at the test and it appears that idle speed can be between 450-1500 rpm to pass, so a hunting idle may pass if CO is still below the 0.3%.