This really bothers me, morning start up (usually before off to work) would took me about 1-2 secs for the engine to start, but after the engine gets hot or after a complete engine stop, would took me about 4-5 secs to start up again. Any idea what cause this?

 

Possible injector leakdown when hot causing flooding of cylinder(s). The longer your car sits overnight the more fuel evaporates and therefore doesn't flood cylinder during restart. This is just a possibility. There is a service port on the fuel rail I believe, although under the intercooler if you have R53 if I remember correctly. If you have a fuel pressure gauge (can get from sears, etc.) hook it up (caution will spray fuel when screwing in gauge due to residual fuel pressure- DEFINITELY DO NOT attempt to install gauge with engine running or key on!!!!!)

Once gauge is hooked up start engine and run till hot. Turn off the engine and watch the gauge, should not drop considerably (more than 20%) unless there is a leak in the system. If system drops down to very low psi after a while say 5-10 mins then it would be obvious that there is a problem. From there you could pull spark plugs and insert long qtip into cylinders till it hits the top of the piston and pull out. See what cylinder(s) come out wet or smelling like fuel which would indicate the problem injector.

Other than this not exactly sure.

Low compression wouldn't make sense because as the engine heats up the aluminum pistons would expand faster than the iron block, therefore only helping compression compared to a cold engine.

Coolant leakage into the cylinder when hot is possible from say faulty head gasket or cracked head but this would also lead to coolant loss obviously.

If the engine is not cranking slowly then any battery, electrical or starter issues would seem out of the question.

Without any check engine light then stuck open purge valve or vacuum leaks when hot would also seem out of the question.


Just thinking out loud there but I would suspect a fuel issue..

 

Try popping off coil pack leads, if you find them corroded clean with emery cloth and put a little di-electric grease on the leads. Have had the same problem and this did fix the cold start issue.


Pictures provided..

http://www.madnessmotorworks.com/min...coil-pack.aspx

 

Caption fr BMW TIS on fuel pressure troubleshooting:

Complaint: starting problems
- Run engine briefly at idle speed and switch off.
- Note down measured value while engine is stopped.
- Read off measured value again after approx. 20 to 30 minutes while engine is stopped.
Special tool 13 3 010 (hose clamp) is required for the following test.
If the measured value has dropped by more than 0.5 bar:
- Start engine and wait briefly for a stable pressure increase.
- Switch off the engine and immediately pinch off the delivery line just before the pressure gauge with the special tool 13 3 010.
- Note down measured value
- Read off measured value again after approx. 20 to 30 minutes while engine is stopped
If the measured value has now dropped by less than 0.5 bar, the following faults can be present:
- Fault in delivery lines
- Fault in in-tank delivery hose
- Faulty pressure-holding non-return valve in fuel pump
Check components. Replace faulty components.
If the measured value has dropped by more than 0.5 bar again:
- Replace pressure regulator
Note:
- All the fuel hoses and hose clips which were detached within the framework of the checks must be replaced.
- Interrogate fault memory of DME control unit. Check stored fault messages. Rectify faults. Now clear the fault memory.

Other possible suspects are coil, plugs, coolant temp sensor. Hope you could pin the right one down,