Cold Start Miss And Poor Mpg

[happygoron 2]

Hi all,

 

My 205 always used to idle and drive spot on. However I had some starting issues a few months ago resulting in me replacing the starter solenoid wire, motor and battery. At around the same time she developed a misfire when starting from stone cold, idle is steady but rarely where it should be and MPG has been geting steadilly worse (low 200 miles to a tank down from 300).

 

When started from stone cold she sounds and feels like she's missfiring for a bit but is driveable. Idle will then slowly rise to 2kish as the misfire clears and drop to 1.5k when fully warmed up. However if restart the car the idle will then be around 1k and will take a while to get back up to 1.5k if it does. Also if the car gets very hot (fan always kicks in and she's never overheated) such as sat in traffic for a while the idle will steadilly drop and drop till she'll want to stall. Hence I don't want to lower the idle screw any lower at the moment.

 

I have done a lot of reading about similar problems on here and have:

• Checked for air leaks.
  
• Replaced and set up TPS
  
• Replaced ECU temp sensor (though connector pug is past it's best, where could I get a replacement)?
  
• Checked mixture (Was MOTed the week before last) - 2% CO at hot idle, a little high but not bad.
  

 

I have a SAD to change but I can't see how this would cause a misfire from cold as she still spluts and judders when throttle is applied when there should be plenty of air.

 

Any suggestions?

[welshpug 1,657]

AFM

 

plug for the CTS you could get from a scrappy, or VWP, Simtekuk polevolt maplins etc.

[pug_ham 244 3 Cars]

How old are the leads, dizzy cap & rotor arm?

 

205's are particularly prone to this kind of thing (imo) when they are getting worn or cheap (intermotor) parts have been used before.

 

I might have a spare CTS plug or at least one suitable for it.

 

I'll have a look & let you know asap.

 

Graham.

[happygoron 2]

Hmm, will try and get hold of another afm to see.

 

Plugs are new and ngk, leads are about a year old and bosch, cap and arm are getting on a bit. What brands should I look for for them? Can't see how they would affect the idle speed much though? If you do have a plug would be great cheers.

[pug_ham 244 3 Cars]

I should've made it clear I was only suggesting these parts for the misfire.

 

Best brand you can find (which I suspect will be Bosch) although not for leads because the Bosch sets of leads I've had always left the end on the plug when removed.

 

Graham.

[happygoron 2]

Right, dizzy cap and arm set ordered from gsf.

 

MPG has improved with the new ECU temp sensor, looks like I'll get around 30 on this tank after a drive to west wales and back used less than half, though I know the guage can have a mind of its own around the halfway mark!

 

Still have the odd idle speed dropping over time (especially in traffic) problem, got back to swansea yesterday and she was idling around 1000 after a 60 mile drive, after battling through the swansea traffic she was around 6-700 with the fan kicking in fine and nothing untoward on the temperature gauges. Will try and source an AFM to see if WPs suggestion is right.

Edited February 28, 2011 by happygoron

[Tom Fenton 1,542]

Remember that there is no idle speed compensation for load, so with heavy electrical load, e.g. rad fan, heater fan, headlights, the extra electrical load on the alternator does drag the idle speed down a touch.

[happygoron 2]

Remember that there is no idle speed compensation for load, so with heavy electrical load, e.g. rad fan, heater fan, headlights, the extra electrical load on the alternator does drag the idle speed down a touch.

 

Am aware of that, not causing the issue in this case, at least nothing I'm switching on or the main fan. My only theory is a componant is heating up causing a change in it's resistance that isn't compensated for? Bit of a long shot.

[happygoron 2]

Update: Changed Cap and Arm, definately needed changing as old cap looked post its best. Didn't fix the misfire though did seem to help a little. Havn't driven it enough to see it's effect on the idle but I can't see how it would help. Double checked for airleaks, she stalled as soon as I covered the afm intake.

 

One thing I noticed is the SAD seems slow to have an effect, When she first starts she'll miss and I need to idle her myself, then she'll struggle to idle and still miss a litle (I can squeeze the sad hose here with no effect), when she warms a little (looking at about a minute) she idles fine at about 1400 and the sad is open, squeezing the tube results in a drop in revs. Should the SAD be open immediently?

 

Also when driving to get the dizzy the other day I payed attention to the way she behaves when restarted hot. By the time I got to GSF she was up to temperature idling steady at 1100ish. When I restarted the car she would idle steady but a bit low at 700ish all the way home. This is common, each time I restart the car she seems to idle a little lower. Surely these issues are linked?!

 

My next step is to try and get hold of an AFM to try and maybe look at new plugs and leads, though they arn't old.

[pug_ham 244 3 Cars]

Should the SAD be open immediently?

Imo on a cold car the sad should be open as that is the normal position, its only powered closed when the ignition feed is there.

 

Any I've got off the car have always been open when I've loked at them.

 

Finding a good quality set of leads might make a big difference, most sets I've fitted recently have been lucky to last 18 months. Basically find the best set you can (not Bosch though imo).

 

Any car would or should stall when you cover the afm intake, it's like covering your mouth so you can't breathe.

 

Experienced the varying idle when warm but never got it sorted (wasn't my car) but it never stalled even when idling this low so wasn't a major issue & the car didn't suffer from kangarooing so they was happy.

 

Graham.

[happygoron 2]

Imo on a cold car the sad should be open as that is the normal position, its only powered closed when the ignition feed is there.

 

Any I've got off the car have always been open when I've loked at them.

 

Finding a good quality set of leads might make a big difference, most sets I've fitted recently have been lucky to last 18 months. Basically find the best set you can (not Bosch though imo).

 

Any car would or should stall when you cover the afm intake, it's like covering your mouth so you can't breathe.

 

Experienced the varying idle when warm but never got it sorted (wasn't my car) but it never stalled even when idling this low so wasn't a major issue & the car didn't suffer from kangarooing so they was happy.

 

Graham.

 

This is why I find it strange that squeezing the pipe has no effect when she's missing + cold but does when she's settled and the idle has risen. My understanding of the sad is that it can only close itself, it can't open without relaxing. Now I'm sure my cold misfire and the idle getting lower with sucessive starts is linked but I can't pin it down.

 

Changed plugs again and leads. Helped the misfire when cold but it's still there. Then had to do 3 short hops (not ideal I know) and first was fine, idle at about 1400 as I would expect when cold. next one it had dropped to 1000ish, next was struggling at 6-700. Odd. So I'm sure basic ignition componants are in good order and I can't see it not getting enough air so i'm leaning to afm/coil/amp/fuel related?

 

I know about the leak test result being good, didn't make myself clear sorry.

[Collier 0]

everything you have said happens to me every time.. i cannot find my sad to replace it? i have an afm ordered so when i have replaced it i will let you know the results.

[Anthony 1,003]

Depending how short the hops are, that lowering idle speed could be expected to a degree.

 

The SAD is closed by heat, primarily by the heater coil inside, but residual heat from the engine and engine bay will do it as well. If the hop is long enough to get the engine and bay warm, and then you park up for a short time, the heatsoak into the SAD will likely cause it to partly close, lowering the idle speed. If it were to fully close whilst the engine is still not upto temperature, it will likely idle low and potentially try and cut out.

 

Also, lean off the AFM mixture screw a couple of turns or so anti-clockwise. Despite being well inside MOT test regulations, 2% CO is too rich and won't be helping matters at all in my experience - I normally set them to run 1% or leaner.