Misfire on start-up

I have a recurring issue with my 52 TF in that when I start it from cold (overnight) it sometimes only runs on 2/3 cylinders and has also on occasion given amounts of steam from the exhaust. It rights itself within less than a minute, but yesterday, the yellow engine management light came on after this had happened (went out when engine was restarted) - I guess this is just indicating that there was a misfire.

The issue only appears to happen when I've either washed the car (large amounts of water through the boot engine vents) or when it's lashed with rain, as it has done over the past month. I've checked the coolant expansion bottle and there does appear to be a very slight drop in coolant level, but we're talking a few MM's. There's no sign of any oil in coolant or visa-versa. I have had a replacement engine fitted as a result of HGF. I have read that this problem can be down to a leaking inlet manifold and I'm wondering if this could be the case as a result of the gasket not being fitted correctly when I had the new engine fitted. Any ideas on this topic would be welcome.

:welcome2:
This certainly sounds like a typical inlet manifold water leak problem. The symptoms of rough start up and steam from the exhaust point that way. This happens more with the plastic inlet manifold than the later/ better alloy manifold but it is not unknown for a later manifold to give problems. You might also be able to see coolant stains below the inlet manifold.

An easy way to tell is to take out the spark plugs. No.4 (normally) will be unusually clean.

Of course there is the other way for water to enter the cylinders, i.e. HGF

Thanks David, I'm hoping that it's not another HGF as the new engine is of the later type and was anticipating that the issue had been eradicated. I'll look at the manifold area first and see where this leads me. I am slightly baffled by this as it only ever happens when there been heavy rain, for the 6 months that the car was garaged with dry weather use - no problems arose.

Worth checking the water temperature sensor - it seems to cause all sorts of problems. Do the radiator fans start up just after starting as this seems to be a good indicator of problems?
I had problems with very rough running and difficulty starting and it turned out to be bad connection to the sensor (a bit of WD40 seems to have sorted it out). Maybe damp is getting to it..

No, the fans only come on under what I would say are the usual conditions - standing in traffic. I will look at this as I do feel there's a correlation with water and this issue. I don't know if it's just coincidence (not a believer if these) but I am losing coolant by the rate of 3 mm in the last 12 months.

I had something similar on my car, usually after washing it. just a slight misfire just after starting. Not done it since I replaced a suspect coil pack with a spare I had.
May treat myself to a couple of new spares next year.

Sundance

I had a misfire.increasing the revs gradually you could feel the imbalance of the engine..plugged in diagnostic kit...pointed to cylinder one....so swapped the coil packs over and checked again...the fault moved to a cylinder on the opposite bank proving the coil pack was at fault...I treated the engine to 2 new coil packs new HT leads and new plugs..plugging in saves time

Nicely sorted.

Which diagnostic kit did you use?
And was this on the 135 in your signature?

Just a cheap plugin from eBay...Bluetooth dongle which uses the torque ap on my smart phone...nifty ap which is free but I chose to buy the professional version because it don't contain pesky ads...dongle was listed for rover cars...probably never paid more than £15 for the ap and dongle if my memory serves me right.and yes it was the 135 in my signature...2004..
Below are the 2 obd results
Pics in the wrong order but clearly you can see the different readings has the coil packs are changed over...a very quick diagnostic in minutes..and the fault code is clearly seen...afterwards the ECU was cleared of fault history

I also have one of the cheap OBD dongles with the Torque pro app. Quite surprised how well it works, but you have to pick the right one for the car, took me three attempts until I found one that worked with the Modular engine management system 3 on my TF. Not such a problem as one worked on my other car.

Sundance

Just a bit of an update. I had the car MOT'd last Friday and a thought check and test of the cooling system by experiences ex-MG technician showed-up nothing on HGF. I've decided to check the plugs first, then possibly replace the inlet manifold gasket - think this will be spring next year as it's too cold to do anything now.