Please help my 1991 245. Here are its symptoms:

1. Hard to start when cold
2. Very rough idle
3. Stumbles under load (feels like the engine isn't balanced)
4. Extreme power loss (it doesn't like to climb hills or accelerate)
5. Very poor gas mileage (smells like I'm dumping unburnt gas into the exhaust)
6. Has been progressively getting worse
7. Have noticed the car runs a little warmer (the coolant has overflowed twice in the last month, which is very uncommon)

The problem started about a month ago. The car ran great but every once and a while when climbing a hill or accelerating it would stumble for a second or two. It was anoying more than anything. The car idled fine and I didn't really notice a drop in fuel economy (8.5 to 9.0 L per 100 km). Now is a different story. The car always idles rough, always stumbles under load and always gets very poor gas mileage (11.5 L per 100 km). I should tell you that once and a while the car starts to run normally. You can suddenly feel the stumbling go away and the engine gets a surge of power. However, this never lasts more than a second or two.

Please remember, this wasn't abrupt. It was gradual, which to me seems like a component slowly failed over the past month. I have searched the archives, read the "7xx/9xx/90 Cars" sections and the Haynes manual with little success. Here is what I have done over the last month:

1. Replaced spark plugs, wires, distrubutor cap and rotor.
2. Replaced knock sensor
3. Checked and replaced main pump
4. Inspected intank pump and sending unit. Replaced in tank pump.
5. Check function of fuel pressure regulator.
6. Checked Air Mass Meter (AMM). With car running I disconnected AMM. Car immediately idled differently. Connected AMM and car ran fine.
7. Check air filter and intake housing. Filter 2 monthes old. I didn't see any cracks in the housing on intake side of AMM. I did notice that the housing and throttle body did have oil residue in it. As far as I have read, a little blow by is normal (please correct me if I'm wrong).

I think thats it, but I may have missed something. Any advice you can offer is greatly appreciated. Thanks ahead of time.

Kindest regards,

Greg