As the title says I'm having an issue with my 2007 Mini Cooper S automatic with a JCW tuning kit. I searched all the forums for anyone else having similar issues but haven't found a cure for my car yet. Other than the JCW tuning kit, the car is stock. When the car is warmed up, if you shut it down and restart it, the engine surges, then the RPMs fall until the car stumbles and then they bounce up and down for a second until it stabilizes. Sometimes the RPMs will fall enough to cause the car to stall. After that, the car runs well, no issues with stumbling when coming to a stop or anything else like that. The car has 60,000 miles. When the car is cold, there isn't a problem. I've had the problem for a while (10k miles).


The car is not throwing ANY codes. I have good diagnostic equipment and can read any values or codes from the ECM (or any other module) but haven't found anything out of the ordinary.


I've done the following to try and remedy the issue:
-Walnut shell blasting of the intake valves and cleaning of the throttle body and intake manifold
-New OEM NGK plugs
-New thermostat and coolant temp sensor
-New timing chain and tensioner (this was unrelated preventive maintenance, the old one was OK)
-Swapped coils from a known working car (no change in my car)
-Cleaned MAF
-Swapped MAF from a known working car (no change in my car)
-Cleaned the vanos solenoid (the one in the side of the head, not on the camshaft)
-Checked every hose from the air box to the throttle body for a boost/vacuum leak. I am almost positive that is not the problem.
-Visually inspected the valve cover for leaks but haven't been able to find any
-Zip tied the rubber PCV hose on the driver's side of the valve cover to be sure it was not leaking.

I think tomorrow I will change the valve cover. I have a used one I can swap out that was working when removed. I do not think this is the issue though. My other suspicion is something related to the vacuum pump, but I don't understand exactly how that works.

Anyone have any idea what I should try next?

 

Can you read the fuel pressure and lambda values and ambient and engine temps? Cold start will be rich, temps should be about correct, if fuel pressure is slightly low but ECU goes for lean mode at hot start it will stumble and correct for lambda, also if temp sensors give a bit off temp, Also check again for any intake leaks, a verry small leak might act like that. It does correct after a bit? After getting things sorted clear the ecu.

I keep at least half operating pressure for fuel pressure, and lambda stays close.

 

for leaks remember the hose that is at the back of the valve cover has a valve to prevent boost loss off vacuum, try blocking it both sides and that its oring and snap in work. Does sound more fuel pump,

the vacuum pump spins a plate in an oil bath, at 60,000 should be ok but it provides for brake and turbo boost. it would prevent boost if lose of vacuum happens but at idle you are in vacuum only.

on vacuum pumps, it is something to replace on maintinace, as it can take out the valves if it gets stuck.

 

I data logged a couple of hot starts. The RPMs are bouncing, but I don't think my logging software was updating fast enough to show it. Logs for two different starts are posted below. Fuel pressure looks OK at >700 psi.

I'm not sure what's up with the ambient air temp. What measures that? The temp sensor behind the bumper? The temp in the instrument cluster is always accurate.

 

I was able to slightly increase the refresh rate. This log consists of 3 starts, with me shutting the car down in between. You can see a little bit of the RPM bounce.

 

Hi I am in the middle of a project on my mini so cant check but psi should be going 1500+ and at rest I keep about 700psi, see the lambda fluctuate with fuel pressure as it tries to correct 114.6psi is low,,,, but manages a cold start, the pump seal may hold a bit better cold and the rich start can work on lower pressure. Anyway seems to be the pump. Do try the dealer as these are known to need replacing. I did see pumps from Peugeot on ebay going for the least amount and Way has second best price. Sadly OEM was -300 now off the charts.

Also UK pound to dollar try some places there, maybe Minigeaboxes uk as they service and do ship to the us

 

I have access to another mini Cooper, I'm going to log the fuel pressure on that one and see if it's different. If it is, maybe I'll swap the pumps before getting involved with the dealer.