Running rough after heavy rain

[JiminyKricket]

My 2.5 10 valve is a pig after heavy rain. It starts ok but will then run as rough as the proverbial badgers as you drive. It regularly loses engine revs and then cuts out, normally halfway across a road junction!!!
Anybody out there with any ideas. The other problem is it has the Fenix 5.2 fuel system and code readers don't work!!

[Baffler]

When was the throttle butterfly valve and idle air valve last serviced?

Inspect the inlet air hose and various vacuum lines for cracks/splits.

After that? ...check the condition of the distributor cap and rotor.

[capt jack]

Suggest you check things as follows:

Look at the fuel filler cap seal. Is it sealing properly or could rainwater be getting into the fuel tank?

Dissy cap and rotor - take them off and clean them - or better still fit new.

Plug leads - examine carefully, especially the one from the coil to the dissy cap. Try taking the engine top cover off and running the engine after dark. If there's a dodgy lead it may well show up as sparks jumping from the lead to the block. If in doubt fit new - from experience plug leads last about 100k miles. Damp will exacerbate failing electricals.

At least check, clean and gap, or better still fit new spark plugs - proper copper-cored single-pin plugs ideally.

Clean the throttle body.

Fit a new airfilter, cleaning any cr*p out of the air box.

Check the engine bay generally for signs of perished hoses.

Check that the throttle cable is sound and moves freely. The sheathing rusts, causing the inner cable to stick.

Do a search on here and invest a few £s in making a simple flash code reader for yourself. It is dead easy and really really useful.

Check that the fuel filter at the back of the car is sound - replace it if it's at all suspect.

Most of this is cheap and easy to do. The Fenix 5.2 system is robust and reliable, and with a methodical approach it'll be possible to cure this.

Cheers

Jack

A further thought - it starts ok then runs rough. Could be that the Inlet Air Idle Valve is sticking in damp conditions. Again, easy to take off and clean up! - J.

[Luxobarge]

Another vote for taking the spark plug cover off and running the engine in the dark - as dark as possible. You'd be amazed at how easy it is to see sparks jumping around, if there are then you can see where they are coming from, and will need to replace that component. It'll be worse in the damp too of course.

[JiminyKricket]

Thanks gents, most appreciated. The electrical side has all been done recently so weather and health permitting I'll check out the fuel system side of things in the next few days. Once again I really appreciate your assistance.

Jim