Stalling...

[Paul Philpot]

Car has been running really well until last night. I had driven about 50 miles but whenever I got to a roundabout or junction the revs dropped and the car stalled. It always started straight away but was 'popping' through the exhaust.

Car is 1994 Supersport 1.4

Any ideas?

[Jonathan Kay]

I think that there's a duplicate post. You can't delete it but you can change the Subject and body text so that all of the responses appear in this thread.

Jonathan

[Jonathan Kay]

Symptoms

1. When it cut out was it always after after you'd lifted off... never at idle or with power on?
2. Did you notice if anything electrical failed at the same time... lights, rev counter?
3. Any recent events... any work on the car, refuelling, refuelling somewhere different, out in the wet?
4. Can you replicate the fault now that you're back at base eg by lifting the engine speed then abruptly closing the throttle?

Signs

1. Quick look at the fuel system in the engine bay: any splits, loose fittings, signs of leakage?
2. Quick look and wiggle at the low tension electrics: battery connections, fat earth cables, feed to ECU.
3. What's your high tension set up? Quick look and wiggle at the plug leads and connections to plugs.

Jonathan

[revilla]

Worth taking the IACV off (Idle Air Control Valve - will be on the inlet manifold and should look like the picture below) and giving it a good clean inside with something like carburettor cleaner. They can get a bit clogged with oily tarry deposits from oil coming through the crankcase breather and it gives symptoms like the ones you describe.

[Jonathan Kay]

Andrew... is acetone OK on that part? (It sounds as if you know from experience!)

Thanks

Jonathan

[revilla]

Err ... probably? But wouldn't like to be held responsible if it did dissolve something. I've used carb cleaner spray before. No sure what's in it and I suspect different brands vary widely but I suspect lots of ether and other things that smell interesting and are bad for you! Best used outdoors.

[Jonathan Kay]

Thanks.

I've used carb cleaner spray before. No sure what's in it and I suspect different brands vary widely...

They certainly do. Ditto brake cleaner. But acetone is pretty common.

I'd always recommend trying gentler solvents such as petrol (!) and isopropyl alcohol before acetone because of the risk of damage to plastics.

Jonathan

[oilyhands]

Not sure if a 1994 engine will have an IACV, it may have a stepper motor..

Oily

[john milner]

I found that WD40 worked better than carb cleaner to loosen an IACV but it can leave an oily residue so may need a follow up clean with carb cleaner.

[Toughie]

Excuse me nerfing in on this conversation, but I'm having a similar problem, but dunno if its the same engine.  My car has been giving similar problems for about the first half or three quarters of an hour of driving, particularly on starting.  The enegine is a Sigma.

Revs lift, then drop, lift then drop and cut out.  I get a similar patter when lifting off or feathering on the approach to junctions and roundabouts.

I've looked for the part you've kindly posted a photo of, but can't see it.

I'm getting concerned as she's just about to go touring in France.

[Jonathan Kay]

I found that WD40 worked better than carb cleaner to loosen an IACV but it can leave an oily residue so may need a follow up clean with carb cleaner.

WD-40 is a mixture of *aliphatic hydrocarbons, that oil and propellant in a very convenient package. I'd expect it to have about the same properties as an organic solvent as petrol. So I'd suggest using petrol from the start if that residue is undesirable. And, as above that carb cleaner probably contains acetone.

I can't explain why it would work better than carb cleaner.

Jonathan

* And we now know those are C9 to C14 alkanes. (Petrol typically C6 to C8. Diesel fuel typically C9 to C6.)

[Jonathan Kay]

My car has been giving similar problems for about the first half or three quarters of an hour of driving, particularly on starting.

And after that there's no problem?

Jonathan

[Toughie]

I'm not convinced I could say 'no problem'.  She feels a bit cautious on the pick up at low revs, and positively stutters when not fully hot.

I'm beginning to find it hard to tell, as paranoia is setting in.  I'm terrified she's going to fail completely while we're in southern France.

[john milner]

WD40 may work better as the oil makes it easier to push the plunger thingy which will help displace the gunk.

[Jonathan Kay]

Good point.

Jonathan

[Toughie]

Again, may I ask which engine it is you're referring to?

[Paul Philpot]

Toughie... K series 1.4. I ran the car this afternoon and it seems fine. I'm going to take it for a longer run during the week and I'll let you know how it goes.

[Toughie]

OK.  Thanks for the response, Paul.  As I have a similar problem, at least I now know that what I'm looking for in the picture is not on my car, which is a Sigma.

Good luck with yours.  I hope she runs well and you get to enjoy what remains of this summer.

[Paul Philpot]

Right here we go...

about 700 miles ago I had: new head gasket (preventative maintenance), water pump, cam belt, tensioners, fan switch, water temperature sender, radiator and thermostat.

Before the problem started I had just filled up with Shell V Power (never had an issue before). The problem started after about 50 miles.

I put a bottle of STP fuel injector cleaner in and the car has been OK... so far.

Hopefully thus has cleared it...

Good luck Toughie, let us know how you get on.

[Paul Philpot]

So... Had ecu remapped to throttle bodies. Ran perfectly for 250 miles then it happens again. Frustrating!!

[john milner]

I have had a crankshaft position sensor fail on me and that made starting difficult to begin with and then impossible but I think they can fail intermittently while the engine is running and cause the engine to stall and/or misfire. Changing one is a relatively cheap and easy thing to try. A good one should read 1200 Ohms across it whereas mine was open circuit, an intermittent one could read anything.

https://www.doityourself.com/stry/warning-signs-of-a-bad-crankshaft-position-sensor

https://www.lotus7.club/forum/techtalk/turning-over-not-starting

It is probably electrical but a dodgy connection can be a pain to find so replacing the fuel filter and if still no good then draining the tank might be useful. If it still had a problem then at least you would know that you had to focus on the electrics. 

For the wiring I would look at a circuit diagram and make a best guess on the most likely wires and work my way through every connector looking for signs of corrosion.

I have also had engine starting and failing problems caused by a faulty battery master switch.

[Jonnyonthewire]

I had a very similar problem over 3 years ago (copy of my original post below) - Not been a problem since:

I have had an annoying problem on my 140 sigma engine where the car idle at cold was very hit and miss for the first 5 minutes until warmed up, often stalling and needing lots of throttle blips to keep it running. It went back to Caterham under warranty just before it ran out and they "fixed it" with a remap. Since then the issue returned within days and the problem has manifested itself even when the car is warmed up. Pull up at a junction = random stall. I have seen others on forums with similar problems with spark plug changes often seeming to fix the problem. A spark plug change made no difference for me. I checked the Lambda sensor and noticed a small amount of corrosion on one of the connector pins. Cleaned that but no difference. I had also noticed a small amount of corrosion on the rear wheel speed sensor connector so I started checking all the other connectors I could find. Turns out the circular 3 way connector that connects to the Idle Bypass valve on the throttle body had one of the pins pushed back in the connector so I guess it never actually worked properly out of the factory. Removed the pin, re crimped the wire that had come off with me pulling it and reinserted it properly into the connector. Just taken the car for a hour blast and guess what. No stalling. Result. I suggest anyone with similar symptoms check this connector.

[Paul Philpot]

Sevens and Classics found a split in the throttle body mount and a leaky inlet manifold gasket. Car now running as it should. Excellent service by S and C.