Running lumpy once warm?

[IWantThatOne]

Hello all,
I'm new to the site and feel a bit cheeky asking for advice so soon but here goes.
I bought my 1990 e30 320i convertible in late August and it has run superbly since. However, the last few days the car will start and run perfectly. If I turn the engine off and then try to start it from warm the trouble begins. My car will start but run very lumpy and won't rev over 2500rpm making it undrivable. It's been in the garage but I've been told they couldn't see any obvious fault.
I'm a bit lost to be honest and as the wife uses it for her short trip to work and dropping/picking the kids up from school I know when it happens again ill get it in the neck!

Any help would be greatly appreciated.

Paul.

[soul4t]

Hi,

Is the engine serviced, all the usual bits?

Mind you I suppose the garage should pick up on that, depending on how much they looked at it.

Does it misfire causing it not to be able to reach 2500 rpm or is it smooth up until then, and sort of limited?

[Grrrmachine]

... the wife uses it for her short trip to work and dropping/picking the kids up from school

This is very indicative of the problem - you're not letting the engine warm up.

These big old six cylinder engines run very juicily from cold to get going. The ECU measures the temperature from something called the Blue Plug (a thermistor) and adjusts the fuel mixture accordingly. On lots of short trips, that means you're chucking loads of fuel in and it'll burn rich, fouling your spark plugs and giving you a weak spark and lower power.

Your issue could also be a failing Blue Plug (it's not uncommon) but for starters give it a basic service (air and fuel filters, change the oil, new spark plugs) and then an Italian Tune Up (drive it like you stole it), and report back.

[Brianmoooore]

Welcome to the zone. Tech. help is what this section's for.
Check the the spark plugs fitted are the correct ones. Especially make sure they're not four electrode ones - M20s don't like these at all.
Very carefully check the big convoluted rubber hose that goes from the air filter/AFM to the throttle body for any splits. They can be difficult to see without removing the hose.
Check the resistance of the blue temperature sensor, measured at the plug for the engine ECU above the driver's right knee. Check with the engine stone cold, and with it at full working temperature.
Be careful not to push your meter probes right into the buckets of the ECU plug, or you will bend them too far apart, and they won't make proper contact with the ECU pins when the plug is refitted. best to push a short piece of 15A fuse sized wire into the plug, and connect the probes to the wires.
Details of which ECU pins and the resistances to expect should be in the wiki.