Lambda Sensor - cold idle probs

[MGBGTMX5]

Had 1.8 1995 Mk1 for several years, runs beautifully. However, I needed a new exhaust so I wanted to treat it with a Moss Europe supplied Cobalt S/S cat backwards section. Nothing too radical. The front down pipe from the manifold to the cat was shot to pieces too so I took some advice and got local exhaust centre to replace the front pipe with a like for like replacement and fit my S/S back box for twenty quid at the same time. Now the car will only start from cold if I rev the nuts off it and it's running rough when hot. No pull from standstill. Not the desired effect! The exhaust centre guys had probs taking the exhaust off the cat and manifold as the studs were very corroded. I suspect the lambda sensor has got mashed in the process. I know they are fragile, right? I know you can - if you know your way around a voltmeter - test if the lambda sensor is working. I don't know my way round a voltmeter, any ideas how else to check? (It's not the infamous leads - plugs - coilpack issue.). Does that sensor sound like the culprit to you guys? Mine seems to be a 4 wire sensor. If we think it's that I guess it's done nearly 20 years service, so maybe it gave up the ghost when disturbed. (Not sure I'd be being reasonable to blame the exhaust centre guys.) Does anyone recommend a good & reasonably priced replacement? I don't want a cheapie so that I have to start cutting the loom to patch it in. I'd prefer to go with plug and play with a Mazda connector atttached. Thx!

[fatjon]

Lambda sensor has zero effect on cold start and cold idle/running. The engine only goes closed loop and uses lambda feedback for mixture control when warmed up to pretty near normal operating temperature.

[fatjon]

But, on reflection. If it's mashed up to the point that it is shorting out wires that could be having a nasty effect on the ECU. A long shot though.

[MGBGTMX5]

OK, thanks for that advice. I had read they don't do much until they heat up to 600 degrees so that makes sense - unless as you say it's that busted it is giving weird feedback signals on cold start and tripping up the ECU. There's also no engine management liight on. Exhaust guys v friendly when I discussed it with them today and they will look it over next w/e when i can get it back to them - so assuming / hoping we get it fixed I'll let you know what the issue turned out to be. Thx!

[MX-5 Lazza]

Does a 1995 1.8 have an engine light?

Have you tried checking for engine error codes?

[skinny]

doesn't sound like lambda sensor to me, i think they broke something else. just not sure what.

[MGBGTMX5]

All sorted. Took 2 mins. Apparently they had pulled off a vacuum hose somewhere between the bullkhead and under where the lambda sensor connector joins the loom. I couldn't see anything loose when I looked. That was why it was tough to get started from cold as no vacuum being created until after about 15 attempts at starting caused enough for it hold (otherwise it instantly stalled) a tickover. Then rough but running, but not nice to pull away as it wanted to stall unless you floored the pedal and then it gave nothing like a pedal to the floor style pull away. But now it's running as great, as great as it always did. And sounds terrific with the Cobalt back-end s/s exhaust too. Hope that may helps others that stubble across that problem.

Next job is to ditch that sticky rear caliper for one from CarFactors on eBay for £35 and then to decide whether to get a fabric and glass roof to replace the original cracked vinyl and plastic, which now leaks. Shall I do it now or leave it until next spring - because it will most likely be hardtopped all winter. We'll see. Heard good things about HotHoods in Romford, so may give them a try. Any other suggested places
in and around Essex?

[MX-5 Lazza]

Sounds to me like they have fixed something but have spun you a line about what it is. There are no vacuum lines back there and even if there was it wouldn't cause the problems you are reporting. The nearest thing relating to vacuum back there is the brake servo line and you'd know if that wasn't connected!