Lack of engine power when cold

[Zagato]

These days, my D-jet 450SE seems to be struggling when cold.
Every morning, or if the engine has been turned off for more than 6 hours, the car hesitates or stutters upon acceleration. In some cases, it sounds as though not all the cylinders are firing! Warm up idle seems fine, despite the high idle speed, but only upon acceleration is when the car struggles to pick up speed. Took around 10 seconds to go from 20 - 60 km/h.

However, when the car is fully warmed up, the engine runs fine and very smooth too.

I checked the spark plugs and they seem fine. I already had all the fuel system hoses replaced, same with the fuel filter, so I doubt it's related to a fuel leak. Unless the fuel pump is at fault.

I'm suspecting that it could be the cause of the transmission. I recently found that the fluid level is too high. So maybe when cold, the transmission is strangling the engine?

Theories? I hope the ignition timing isn't at fault. Or worse, if the timing chain skipping a tooth.

[s class]

Why are you so worried that maybe the ignition timing is wrong?  It only takes a few minutes to check and adjust?

you need to check and correct the transmission fluid level, to avoid damage to the transmission.  It must be checked with the engine idling, after reaching operating temperature, and with the transmission in 'P' or 'N'. 

As far as fuel is concerned, either an excessively rich, or an excessively lean mix during the warm-up phase can lead to poor performance. 

Certainly, I would check the fuel pump's delivery rate and pressure. 

If you don't have any other mechanical noise symptoms, it is not likely that the chain has jumped.  However, again it is worth checking.  It only takes an hour to remove the valve covers, rotate the engine by hand, and close up again.  On this topic, given that the M117 does have a weakness in regards to chain issues, has the chain, tensioner and guides been renewed?

[Zagato]

Why are you so worried that maybe the ignition timing is wrong?  It only takes a few minutes to check and adjust?

You're right, I'd forgotten ignition timing is easy to correct. Shouldn't worry about that then.

you need to check and correct the transmission fluid level, to avoid damage to the transmission.  It must be checked with the engine idling, after reaching operating temperature, and with the transmission in 'P' or 'N'.

Checked the fluid with engine running, the level is too high. I'll get that sorted with a fluid and filter change, as I don't know when it was done last anyway.

As far as fuel is concerned, either an excessively rich, or an excessively lean mix during the warm-up phase can lead to poor performance.

I believe an excessively rich, or excessively lean mixture could be the cause.
I've been informed by a specialist mechanic that the cold idle valve is sticking open during warm up. So the fuel mixture must be very off when the car is warming up.

On this topic, given that the M117 does have a weakness in regards to chain issues, has the chain, tensioner and guides been renewed?

I haven't got a clue, to be honest. When I bought the car, the only service history it had was what's recorded in the provided service booklet. Apparently its last proper service with the dealer was at 175,000 miles, as that's the end of the booklet. The car currently has 205,000 miles. Those components may have been changed already, but I have no written evidence of it.

[Kris P.]

If your's is a d-jet, try checking your air slide valve, it might be clogged up with corrosion  and doesn't give out the right mix of air when its cold.  It usually opens to let air pass through when its still cold to have the optimum mix of fuel and air.  Does your engine shake in the morning when its still not warmed up?

[Zagato]

Does your engine shake in the morning when its still not warmed up?

Upon start up, the engine coughs twice and then into a smooth idle, with some metallic rattles from what sounds like poorly calibrated tappets. The rattles go away when warmed up.

[TJ 450]

A metallic rattle at startup could also be the timing chain... they get very noisy when worn out. It's also very easy to check if the chain has been replaced... wear is obvious visually and the plastic rails will be dark brown.

It only takes a few minutes to check on the 450 and the gaskets are reusable rubber.

Tim