Poor idle/stall on start up

[philip600]

Hi,

I've just replaced the exhaust & O2 sensor on my S4S.

Now when I start the car although it starts ok the idle soon becomes erratic, hunting between 400rpm & 1200rpm. Sometimes it stalls.

It will start again ok but within a few seconds will do the same again.

It will do this whether cold or even after been stood for 30 mins from hot.

Within a couple of minutes it settles down & is ok ?

I have re-set the IAC as described in Freescan manual but still the same.

With ignition on the IAC is showing as 170, once started this goes up to 240 before eventually settling down to 40.

I presume it is the IAC that is causing the problem but what can be done with it ?

Any help appreciated.

Regards, Phil.

[Bibs]

They're cheap and easy to fix but first take it out and give it a clean. I assume you've reset the ECU too?

[philip600]

Hi Bibs,

Yes I reset the ECU.

Where is the IAC located ?

Phil.

[Bibs]

They're about £25 I think in case you're is knackered (and it won't be the first!)

[philip600]

Thanks again,

Took it out & found the 'o' ring was persished & split. Cleaned the valve & replaced 'o' ring but still the same, looks like a replacement is required.

Phil.

[lotus4s]

Are you using an OEM O2 sensor or a cross reference?

Edited September 28, 2011 by lotus4s

[Vulcan Grey]

The IAC sounds like it is working correctly, if it is stable between 20-40 at idle when fully warm...

You could have another air leak from the one of the hoses connected to the intake manifold, or possibly one of the gaskets.

Which O2 sensor did you get?

I recently replaced mine with a BOSCH 13030 and it fit's and works perfect.

Edited September 28, 2011 by Vulcan Grey

[philip600]

The IAC sounds like it is working correctly, if it is stable between 20-40 at idle when fully warm...

You could have another air leak from the one of the hoses connected to the intake manifold, or possibly one of the gaskets.

Which O2 sensor did you get?

I recently replaced mine with a BOSCH 13030 and it fit's and works perfect.

Hi,

The reading was stable once warm but it was up to 240 when initially started & it states maximum 170 in Freescan book ?

This is why i thought it was the IAC.

I have noticed tonight though that the exhaust looks a bit sooty ? don't think it was this bad before, could this be linked ?

Once warm the car is running fine.

The O2 sensor was from SJS ( £ 50.00 one ? )

Another thought is that I recently removed the plemnum cover to access the charge cooler but I made sure It was re-sealed well & I did drive it after this work was done & this fault was not apparent, it appears to have only occured since the exhaust / lambda sensor were changed although this could be coincidence.

I'm open to anymore suggestions but will check for air leaks as well.

Thanks, Phil.

[Vulcan Grey]

The EMH manual says that the IAC typically starts at 170 when the car is cold, before you start it.

In my experience it can go up to 240, but then it will come down as the engine warms up and should be between 20-40 when the engine is at idle and fully warm.

I have data where it started at 168, went quickly up to 240, and then down to ~35, and the car was running great that day!

If you aren't sure your IAC is ok, then you should follow the steps for "code 35" in the EMH manual. That procedure will also help determine if it is an air leak as well.

Edited September 28, 2011 by Vulcan Grey

[philip600]

Hi,

Excuse my ignorance but whats the EMH manual ?

If it was an air leak would it not do this all the time or could it improve once warm ?

Is there an easy way to check for air leaks ?

Could this cause exhaust to be sooty ?

Many thanks, Phil.

Edited September 28, 2011 by philip600

[Vulcan Grey]

the parameters for the engine running are different between cold and warm, and also between idle and driving. A small air leak may not hurt the engine while driving, but it can cause stalling at idle.

The EMH manual is a part of the Lotus Esprit shop manual, but it didn't always come with the shop manual. You often have to buy it separately. The EMH manual is the Engine Management Section for all of the chargecooled cars, SE, S4, S4s, GT3, Sport 300, X180-R.

If you are a member of this site, then you can download all the manuals, including parts and EMH manuals.

Here is the Code 35 page for example

[DanR]

Check your TPS voltages too. If it's outside .45 to .7v but you're getting the proper IAC count your base throttle plate stop could be out.

In closed loop is the o2 swinging either way above and below .5v. If so your o2 sensor should be fine.

With Tech 1 there's a fuel interpreter which if over 128 is adding fuel and if under 128 is leaning. If freescan has something similar that shows fuel is being added you could also suspect an air leak.

Your spark at idle (hot) should be around 5-11degs.

[philip600]

Thanks Dan,

I'll get Freescan plugged back in tonight & check a few more things.

You say if over 128 is adding fuel & under is leaning but in my Freescan book it states the opposite ? ( BLM contents )

It says ideal is 128, values less are ok ( presume this is rich ? ) but above this it is running lean, seek advice ?

With the exhaust being sooty I'm now thinking it may be an air leak.

Will let you know how I get on.

Regards, Phil.

[philip600]

Check your TPS voltages too. If it's outside .45 to .7v but you're getting the proper IAC count your base throttle plate stop could be out.

TPS voltage seems fine with values as above when the throttle is pressed.

In closed loop is the o2 swinging either way above and below .5v. If so your o2 sensor should be fine.

Again, this seems fine & swings form 0 to 0.9.

With Tech 1 there's a fuel interpreter which if over 128 is adding fuel and if under 128 is leaning. If freescan has something similar that shows fuel is being added you could also suspect an air leak.

This was showing 127 at idle.

Your spark at idle (hot) should be around 5-11degs.

This was 14.8 with warm engine.

I plugged Freescan in tonight after replacing a couple of vacuum hoses & checking all connections, I also removed the plenumn chamber & fitted a new gasket.

With ignition on it was showing -

IAC - 170

Desired Idle - 1387

MAP - 0.9

Barometer - 0.85

O2 Volt - 0.462

Spark Advance - 74.9

BLM - 127

BLM Cell - 19

After start up it showed the following after a few minutes but the problem was still present.

IAC - 240 dropping to about 70 after a few minutes.

Desired idle - 2237

MAP - 0.55

Barometer - 0.85

Spark Advance - 14.8

BLM - 127

BLM Cell 19

After a couple of minutes of poor idling & a few stalls it all settles down & is fine.

If I try to drive away whilst this is happening it dies & you have to rev it to get it going although sometimes this doesn't work & even though the throttle is partially open the engine will not pick up.

I tried unplugging the IAC & it made no difference so I suspect this shows the IAC is fine ?

Any further suggestions or comments on the above readings ?

No fault codes showing up.

Regards, Phil.

[Vulcan Grey]

IAC of 70 will cause stalls at first touch of throttle.

Look for air leaks, and then if none, use Freescan to adjust the minimum air rate bleed screw to get IAC between 20-40 at idle with fully warmed engine. Go very slow and let the IAC stabilize between adjustments. Turn the flat head screw driver ~1/16th of a turn each time, very small amounts!

[philip600]

Hi,

You suggest looking for air leaks, by this do you mean vacuum leaks on the inlet manifold ? In the freescan manual it says to check MAP values & if these are the same as Barometer readings suspect vacuum leaks but my MAP value was 0.55 against 0.85 BAR so does this suggest no leaks or could there still be leaks somewhere ? ( Freescan says MAP should be 0.45 - 0.5 )

The engine was not fully warmed when the IAC value above was taken ( running for about 5 minutes ) Earlier in this post I took the car for a run & IAC value was down to 40. How quickly would it normally reduce to the lower value ?

I was thinking about the IAC as it suggested in the servive notes you kindly posted that if the IAC is disconnected & the fault is still apparent ( which it was ) the IAC valve cannot be the culprit. Is it possible though that the valve is not moving & is stuck in a position that is ok for a warm engine but when cold it is causing it to stall ? I presume the readings given in Freescan are what the ECU is sending to the valve in order for it to move to the correct position & therfore does not prove the valve is actually working ?

Appreciate your time & input on this.

Kind regards, Phil.

[Vulcan Grey]

I don't think the IAC is the culprit. But it does cause issues when it is compensating for another problem, either minimum air rate bleed screw maladjustment, or air leaks.

The manifold doesn't see much vacuum, due to the turbo boost, so I don't usually call them vacuum hoses, but they look just like vacuum hoses that you see on normally aspirated cars. There are several that connect to the intake manifold. check all of them, and any elbows or connectors for cracks. The hose from the fuel pressure regulator to the intake manifold Tee, under the chargecooler box, often gets pinched or chaffed by the chargecooler, and cut open.

The IAC counts should get down to between 20-40 at the same time the engine reaches normal operating temperature of ~80C.

the IAC is a stepper motor, so the ECU can actually read it's position as well as command it. However a broken o-ring or dirt can cause it to let more air past than the ECU wants, so that is why the ECU will attempt to compensate and go out of a normal range. Same goes for air leaks.

A very small leak will raise the MAP somewhat, but not necessarily to the same as Boar, but that would still be enough to cause a stall.

[DanR]

What do you mean by:

TPS voltage seems fine with values as above when the throttle is pressed.

Your TPS voltage should be between .45 and .7 WITHOUT pressing the throttle.

Also all check values should be after the engine's at normal operating temps.

[philip600]

Hi Dan,

The readings on the sensor diagnostics page were .7volts while at idle with a zero in the scaled box, then when the throttle was pressed the scaled box showed a reading & the volts value changed as well.

It says in the manual that the TPS volts & scaled values should very between 0.45 & 4.5 volts while slowly depressing the throttle.

Also with ignition on the throttle position shows 0 & when the pedal is pressed fully down it shows 100, is this reading taken form the TPS, & if so I can take it the sensor is set correctly ?

I'm concerned about the sooty exhaust, could air leaks cause the engine to run rich ?

I will also re-check values with the engine warm but was trying to see if anything was amiss whilst it was first started as this is when the problem occurs, after a few minutes it settles down & runs fine ?

Many thanks, Phil.

[DanR]

Probably the throttle angle. In degrees on Tech 1 so maybe the 100 is a percentage on your Freescan. Somebody else with Freescan could advise on that.

I like to adjust the TPS midway, about .55 as .7v is max.

On a cold engine (overnight) the following values should be displayed (on Tech 1 anyway) with key in "ON" position engine not running.

IAC 170 TPS .45-.7v Throttle Angle 0-95degs (WOT) Spark 75deg Fuel Integrator 128 o2 approx .455v and open loop Block learn cell 19 Knock 0 and no signal Battery about 12v QDM A no B yes

With the engine running at NOT they are 985rpm IAC 20-40 TPS same Throttle Angle same Spark 5-11deg Fuel Integ 128-140 o2 50-1000mv and closed loop Block learn cell same and locations 90-150 Battery 13.5-14.5v QDM A&B no Purge 0-100 Sync Pulse 0-2

The exhaust is sooty, at least it is on other cars and mine.

Oh and cold the MAT should be around ambient temp, Map and Baro about the same. At NOT the MAT will be more than ambient (heat soak etc) and MAP less than Baro since there's vacuum in the plenum during idle.

Edited September 30, 2011 by DanR

[philip600]

Hi again,

I didn't have a lot of time to plug Freescan back in over the weekend but I did check all air lines suggested & also cleaned the plugs & sockets for the TPS, IAC, & O2 sensor & checked the spark plugs ( these where all nice brown colour ) but fault still there.

What I did notice was that the car will start fine when cold, warm & hot but within 20/30 seconds the problem starts with an initial drop in tickover & a reluctance to rev if the throttle is pressed, sometimes pressing it just stalls it other times there is a delay & then the engine will rev but sometimes misfires.

If I try to drive off the engine dies & sometimes stalls.

Within a minute or so of this it all settles down & behaves normally.

Will hopefully have some time to plug it back in this week & have another go.

Phil

[superdavelotus]

Hi Philip,

I suspect the O2 sensor. If your car is running rich too since fitting it and the exhaust system plus this idle problem then I would look at this first. I know it's a new one but at £50, it will be a patten copy not a genuine Lotus one. Some are good and others not so. Also the wiring length of the O2 sensor is very sensitive to the readings it gives. With a copy O2 sensor some vendors buy in universal ones and solder on the plug/ pins. Also the universal or patten ones might have a different wire length.

David

[philip600]

Hi David,

I am starting to wonder about the O2 sensor although I bought it off SJS so hoped it would be of satisfactory quality even though it is not a genuine Lotus one.

I think I'll e-mail them about it & see what they say, it does seem a strange coincidence that the problem occured since I fitted it.

I did wonder if if was giving poor readings until it warms up a bit.

Thanks, Phil.

[DanR]

Is the old o2 sensor good enough to refit and see what happens?

[philip600]

Hi Dan,

That would have been the first thing to try but it is in poor condition & my attempts to remove it only succeeded in snapping one of the wires off, hence the reason to replace it. It would be good to try it though so I have soaked it with WD40 & will attempt to get it out to to give it a try if only to eliminate it as a possible cause.

Will let you know.

Phil.