Lambda Sensor

[Sandgrounder]

Hi, Does an S3 have one of these or is it just S3C?

If not, how does ECU understand what the exhaust emissions are?

Just to explain, I have some rough-ish running (power a bit lumpy at lower speeds/rough idle) and trying to figure out probale area to look at.

Thanks

[Scoobimax]

I suffered similar and it was a dodgy connection to the throttle pot.

I know, I couldn't believe it either - who would have thought, an electrical niggle with a TVR?!

[phillpot]

Sandgrounder said:

Hi, Does an S3 have one of these or is it just S3C?

Just the S3C.


Would dirty sensors in air flow meters give your symptoms?

Maybe, as suggested, a poor electrical connection somewhere?

[Julesprivate]

Sandgrounder said:

If not, how does ECU understand what the exhaust emissions are?
Thanks

It doesn't... It doesn't really need to as (thankfully) the electronics are quite simlpe on these cars (the ones without the cat at least).

Rough running is one of the PITA things to find on a most cars, thankfully on older ones it's a bit easier to start with the obvious candidates:

Air Filter
Plugs
HT Leads
Dizzy Cap
Rotor
MAF (Air Meter)
TPS (Throttle Position sensor)
Air leaks (check the intake hose)
Fuel Pump circuit (the relay inparticular)
Clogged/blocked injector

I know that's a long(ish) list but they're all relatively simple to check for any obvious signs of wear/damage.

The last time I had a rough idle issue (on my old Alfa) there was a leak in the inlet hose and a faulty TPS..

[Sandgrounder]

Many thanks for the suggestions gentlemen, to expand on my original, I have so far (since buying the car), replaced:
- Air pipes from AFM to throttles
- Air Filter
- Dizzy cap
- Rotor arm
- HT leads on order (thanks Philpot)
- Checked spark Plugs (they look quite new)
- Cleaned AFM's
- Cleaned Idle Speed Control Valve
- Replaced leaking exhaust manifold gaskets.

There is no obvious leak in vacuum pipes, but will have another look.

When it comes to electrical connectors, how can you clean the female part? (in case corroded) A small screw driver made of abrasive particles would be ideal!!!!

Much appreciated,

Graham

[Sandgrounder]

Just a thought, the vacuum pipe/tube from throttle area rearwards towards distributor looks like clear plastic syphon tube (similar to that used by my father back in the 70's when he used to make his own wine).

Doesn't seem very rigid to me, so I can imagine it deflating if subjected to any degree of suction.

Is this the same on all S's or has mine had a subtle modification?

[GadgeS3C]

Sandgrounder said:

Just a thought, the vacuum pipe/tube from throttle area rearwards towards distributor looks like clear plastic syphon tube (similar to that used by my father back in the 70's when he used to make his own wine).

Doesn't seem very rigid to me, so I can imagine it deflating if subjected to any degree of suction.

Is this the same on all S's or has mine had a subtle modification?

Black "neoprene" type tubing on mine.

[Sandgrounder]

I've checked the things I know how to check (don't understand how you can check the injectors??), but don't want to waste any more 'driving' time with my head under the bonnet. I still have clutch hydraulics to sort, but as I can still change gear, that is not utmost priority.

Car booked in to a mechanic this week for a full diagnostic check.

Just want it running smooth while still some summer left!!

[Sandgrounder]

Update: Car back from mechanic at last.

Had to put new silicone pipes on in place of the aluminium pipes, but I knew that wasn't cause of problem.

He checked a multitude of things, and overall I now have peace of mind regarding condition of the engine, however the primary issue he found was incorrect valve clearances. One piston was at 80psi compaired to the others at 170psi. Once he reset them, all are now approx the same.

He also said he had adjusted the Mass flow meter (is that the AFM?), but I didn't know there was any adjustment possible. And cleaned throttles (though I had already done the front of them).

Anyway, the idle has improved (though slightly faster) and the lumpy running at low rpm seems cured. Happy days!

The only negative is that the car "seems" a little bit slower on acceleration (unless I am imagining it).
I'll see how it goes for a while as I am just happy to have it back. But has anyone experienced anything similar?

Thanks

[mep12345]

that compression imbalance would do it.

wrt adjusting the MAF (or AFM) in simplistic terms this is what sets your mixture and emissions, basically there is a recessed screw on the top of the AFM nearest the wheel that you turn to adjust the amount of air allowed to bypass the AFM. The ECU fuels the car based on amount of air flow sensed by the AFM, hence more bypass flow = weaker mixture and vice versa.