Poor idle/stall on start up

[Bibs]

It's very common for anything other than an OEM O2 sensor to cause problems. Get the proper one, you're problems will be over

[sailorbob]

I fitted a SJS lambda sensor and it's been fine. It is an AC Delco (Delphi) AFS99 which AFAIK is OE fitment.

[ramjet]

You say you've replaced the exhaust so I presume no exhaust back pressure valve? If not, than that is my plethora of knowledge extinguished other than.....

(I'm gonna get some mileage out of that pic. )

[Bibs]

I fitted a SJS lambda sensor and it's been fine. It is an AC Delco (Delphi) AFS99 which AFAIK is OE fitment.

Then you were lucky.

Let's take the evidence. O2 sensor was changed for non-OEM part, cars' suddenly got a problem...

In my experience of reading the posts of hundreds of owners, many, many more people have had problems with non-OEM sensors. If Lotus start with a Bosch unit and do something to it, or rub magic dust on it I don't know but these people with problems invariably find they disappear with the correctly supplied part.

[philip600]

Hi All,

I received a reply from SJS who has suggested thit is doubtful the problem is the O2 sensor as it takes a few minutes to go to 'closed loop' & only then does it affect fueling ? This fault happens within 20 or 30 seconds after starting ?

He has said It could be faulty though & I can either buy an original type sensor from them & send this one back to test or send it back anyway but this would mean the car off the road. If it's faulty they will then refund the cost.

I tried to get the old one out but it's going nowhere & looking at the wires I doubt it could be repaired even enough just to try it.

I did read about sensors but thought it was mainly cheap e-bay ones etc I would have thought it doubtfull SJS would supply sensors that didn't work ?

Not sure where to go next other then connect Freescan back up & double check all parameters.

It'll be something simple no doubt !!

Thanks, Phil.

[sailorbob]

You should expect the lambda sensor voltage to oscillate between about 0.1 and 0.9 volts at idle, cycling about once or twice per second, when in closed loop fuelling.

[philip600]

You should expect the lambda sensor voltage to oscillate between about 0.1 and 0.9 volts at idle, cycling about once or twice per second, when in closed loop fuelling.

Hi,

According to Freescan this is exactly what it is doing.

Can someone help me with this question though.

Am I correct in thinking the O2 sensor tells the ECU how much oxygen is in the exhaust & from this reading the ECU works out the fuel / air ratio for optimum performance depending on other factors ie temperature, speed etc.

Freescan only shows the voltage oscillating up & down between 0.1 & 0.9 volts which I presume is rich & lean but what if the sensor is faulty & telling the ECU the is x amount of oxygen why if fact the amount is y ?

Or put it another way the oxygen reading is say 0.4 volts but it is reading this as 0.9 volts ?

Does this make sense or have I got it completely wrong ?

Another quick question if that's ok, if the O2 sensor takes a few minutes to warm up & work properly, what controls the fueling when the engine is first started ? Reason I ask is that on a carb engine similar symptoms would suggest that the choke has been left out too long or pushed in too soon ?

Regards, Phil.

[sailorbob]

Lambda sensor don't fail that way, they tend to get slower to respond or bias the voltage one way and eventually peg.

The sensor does start working a lot quicker than a few minutes. The sensor is only used in 'closed loop fuelling'; i.e. when the ecu is targeting a stoichiometric A/F ratio and the lambda sensor can provide feedback to the ecu about how close to stoichiometric the fuelling is. At other times the ecu is in open loop fuelling and relying on the programming to target the desired A/F ratio (along with adjustments learned from when in closed loop fuelling).

[DanR]

What did you did to change the exhaust? Did you do anything with the EBPV and throttle jack systems and solenoids?

[philip600]

Hi Sailorbob, thanks for the info, I'm a bit clearer with how it works now.

Dan, EBPV was already disabled before I bought the car. Valve was wired open & vacuum pipe from solonoid plugged.

The throttle jack is still present & has a short section of rubber tube that has been plugged off, again before I bought the car.

Is this ok ? I know they advise removing the throttle jack but thought this gave high tickover if they jam ?

Obviously the EBPV now gone.

Plugged freescan in briefly tonight & adjusted TPS, initially it was showing 0.75v at zero & 4.73v at 100%

This was adjusted to give 0.49v at zero & 4.59v at 100%.

Couldn't start it up as it was late & it's pretty loud now, don't want to upset the neighbours

I've been reading more posts about O2 sensors tonight & as Bibs said there are quite a few with similar problems after replacing it with non standard ones ?

Will hopefully get chance to start her up tomorrow & if adjusting TPS has made no difference I'll have to order an original Lotus O2 sensor & hope it's that.

Many thanks to all who have posted suggestions, I do appreciate all this advice.

Phil.

[philip600]

Me again,

Had an idea last night but not sure if it will work.

Would it be possible to unplug the O2 sensor & start the engine ? I know the CEL will come on but wondered if I could try this to see if the O2 was at fault ?

Phil.

[sailorbob]

Yes, you can unplug it, it will remain in open loop fuelling.

[mr.oogieboogie]

If you still want to eliminate the o2 sensor I have a spare that had about 100 miles on it I can send it to you to check ,not looking to sell it but it will at least rule out the o2 sensor

[philip600]

Update -

Just been out & started her up after altering TPS settings last night ( see above )

Started ok as usual but no sign of fault

Left here at tickover for 5 minutes & still no problem, tried AC, idle increased slightly, turned it off, slight decrease but no sign of low tickover or stalling, all good.

Went for quick run out to warm her up & put some fuel in & she is driving like a dream

If fact she was flying, probably in part due to the drop in ambient temperature since last week.

Parked her up in the garage while I had my tea & just been out to start her up again & still ok so it looks like it may well have been the TPS being out of adjustment.

Don't understand why so perhaps someone can explain. If the TPS voltage increases when the throttle is pressed & mine was originally at 0.75 volts ( insteasd of 0.49v )this would have told the ecu the throttle was open more than it was ( please correct me if I'm wrong )

So on this principle the tickover should have been higher, no ?

Could it have something to do with the new exhaust being more free flowing ?

If it's solved the fault I'm more than happy but would just like to understand why it could effect it so much.

Other querry is that if the voltage readings where too high for a given throttle position could this cause the engine to run rich ?

Any information on what problems the TPS would cause if it was incorrectly set would be appreciated.

I also had a look at the back box & cat pipe I took off & they are actually quite sooty black as wel so it looks like this has not changed.

I'd like to thank everybody for all the help in sorting this ( & Peter for offer of a loan of an O2 sensor )

Many thanks, Phil.

Edited October 4, 2011 by philip600

[mr.oogieboogie]

No worries hope it's sorted.

[sailorbob]

I wouldn't have thought that the TPS giving 0.75v at closed throttle would have caused the problem as it's sufficiently close to the recommended value. That said, a guess as to what may explain it is maybe that part of the track is worn and giving erratic readings.

[DanR]

Good to hear.

Since your TPS was out re-check your IAC count at NOT. Adjust the throttle plate stop screw if the count is wrong. These engines can be quite smooth and tractable when tuned correctly.

[philip600]

Hi Danny,

Still working ok

I checked the IAC count last night after a 15 minute run, coolant temperature was at 80 degrees & IAC was showing around 70.

Do I need to reset it via Freescan first & then check again ( ignition on count was 170 ) or can I just get her up to temp & alter the throttle plate stop screw ?

Also has anyone got a picture of the throttle plate stop screw ?

I can see one flat head screw just below the rubber hose on the plenum, this is pointing straight up & can be seen from the back of the engine when i'm sat in the boot, there is also what appears to be a plastic cap on the part where the throttle cable runs around a disc, this is horizontal & can be seen from the back of the engine, again under the rubber intake hose to the plenum.

Many thanks, Phil.

Edited October 6, 2011 by philip600

[Vulcan Grey]

Green arrow=minimum air rate bleed screw. Never adjust without the aid of Freescan or other scan tool, and only do so by following procedure in manual! Always ensure no air leaks in manifold first.

Red arrow=throttle butterfly balance screw. NEVER adjust, NEVER disturb!

[sailorbob]

Don't get hung up on using Freescan to reset the IAC, the ecu does this itself during running to check it's zero position.

[Vulcan Grey]

Hi Danny,

Still working ok

I checked the IAC count last night after a 15 minute run, coolant temperature was at 80 degrees & IAC was showing around 70.

Do I need to reset it via Freescan first & then check again ( ignition on count was 170 ) or can I just get her up to temp & alter the throttle plate stop screw ?

Since your IAC is still high when fully warm, you should adjust it with the engine running at idle (and ~80C) to between 20-40 counts in Freescan. Your IAC being at 70 will cause exactly the stalling issue you originally mention when first starting the car and pressing the throttle pedal the first time.

The screw you need to adjust is inside that protective aluminum cap under the GREEN arrow above. It is a flat head slotted screw, and a flexible shaft screwdriver helps there.

[philip600]

Gentlemen, many thanks,

The picture confirms the screw I need to adjust.

I will have a go over the weekend.

Just to confirm I have no stalling issues now but idle was a little high ( approx 1100 rpm ) which is why I checked the IAC count.

I presumed this will reduce the idle speed ?

Phil.

[Vulcan Grey]

No the IAC will control the idle speed, which is why you need to monitor the IAC while adjusting the minimum air rate bleed screw, as the IAC will continuously fight any change you make. Having the minimum air rate bleed screw in the correct range will help the IAC do its job better. Normal idle should be about 980rpm when warm, but will be higher when the engine is cold. The IAC is able to do this even if you have removed the throttle jack.

[DanR]

Everything Travis said.

I expect your throttle plate will need to be opened a tiny bit which will bring your IAC count down. Idle should drop to around 985rpm. With your TPS volts and IAC count correct you should be pleasantly surprised with how smooth and tractable the engine will be.

You may need a flexi-screwdriver or removal of the cylinder around the adjustment screw.

Edited October 6, 2011 by DanR

[philip600]

Ok,

Adjusted IAC count to approx 38 with throttle plate stop screw ( is this also called minimum air rate bleed screw ?)

Idle now approx 990rpm & very smooth.

Car now starts, idle's & runs very well so good job done.

Just been out to take my friends son out in her & she is flying at the moment, I think the combination of new sports exhaust, new charge cooler pump impellor & adjustments to TPS & IAC along with nice cold ambient temperatures tonight show just what the 2.2 engine is capable of.

Thanks for all the advice from everyone, hopefully this post may help someone with a similar problem.

Regards, Phil.