Engine Miss fire and hesitation

[Alloy]

I wonder if anyone can help.

I have a low mileage (52k) MGF 2001 which I had sitting around all winter sorned. I got it back on the road but it has developed a mis fire and hesitation both when warm or cold. It’s ok for the first minute then problems from then on.

I have changed the fuel filter and taken tank pump out of the tank to clean which it didn’t need.

I bought a cheap scanner and it showed cam sensor and lambda. My assumption was these may show anyway with a bad mis fire as a symptom not a cause. Even so I changed cam sensor and coolant temp sensor. I also replaced coil packs, spark plugs and leads. All have made no difference.

I could go on replacing sensors - lambda, crank, idle control etc but suspect there is a more systematic approach.

Any advice appreciated.

[Chris Tideswell]

Is this the MPI or VVC engine?

[Alloy]

Mpi

[Barbour]

Perhaps a reset of the throttle position sensor will help:

- Turn the key to position II.
- Give it full throttle 5x
- Then wait 15 seconds
- then start the engine.

Also, a bottle of injector cleaner before a refill helped a lot on my F and TF, old petrol tends to gum up injectors etc, worth a try I guess. Are you running on 98?

[Alloy]

Thanks will try that. Premium petrol make a difference ?

Tx

[nigelandjo]

New leads needed possibly. Coil packs starting to fail?

[Barbour]

Thanks will try that. Premium petrol make a difference ?

Yes.

Don't use 95/E10 anyway, they don't like it..

[Alloy]

I have unplugged the lambda sensor and the misfire stops so I think I should conclude I need a new sensor. My question is should I bother if the engine seems to work without this sensor plugged in ?

Thanks

[Barbour]

I have unplugged the lambda sensor and the misfire stops so I think I should conclude I need a new sensor. My question is should I bother if the engine seems to work without this sensor plugged in?

Yes, it's there for good reason.

[talkingcars]

Perhaps a reset of the throttle position sensor will help:

- Turn the key to position II.
- Give it full throttle 5x
- Then wait 15 seconds
- then start the engine........<snip>

It is actually "firmly and fully depress the gas peddle fully 5 times in 30 seconds" and "wait 30seconds".

[talkingcars]

Thanks will try that. Premium petrol make a difference ?

Yes.

Don't use 95/E10 anyway, they don't like it..

All MGR cars since '96 are designed to run on E10.

[Barbour]

Perhaps a reset of the throttle position sensor will help:

- Turn the key to position II.
- Give it full throttle 5x
- Then wait 15 seconds
- then start the engine........<snip>

It is actually "firmly and fully depress the gas peddle fully 5 times in 30 seconds" and "wait 30seconds".

All MGR cars since '96 are designed to run on E10.

I stand corrected...

[CubMG]

I had the same problem on my 01 MPI it was the first Lambda sensor before the cat , I bought a replacement and went to a local exhaust center who managed to remove the old one .it needs to be on a lift for access . The car runs better now , Running with it disconnected may cause it to over fuel which is not good.