Choking out on start up.

[willworkfore30s]

So I finally got my tags for my "free30" last Friday after buying it in September.  I have driven the car everyday since, and have gone through about 1 and 1/2 tanks of gas.  The gas in the car sat in the tank for about a year.  When I got the car the motor in it had a loud grumble in the bottom end when trying to turn it over so I pulled it and put in a 150k m42 and g240.

It ran well for a while but then I upset the vacuum leaks by pulling the head and intake to paint them.  So I did the mess under the intake by capping the plastic pipe and block port.  

So the car has been running pretty well since.  The CEL comes on about 50% of the time that the car is being driven.  Car does not over heat.  It never even gets to the half way mark.

One known issue with the motor right now is that I need a new alternator bracket because it is stripped out and my alt belt is a little loose.

So knowing the background, my real question is:

When I start the car up most every time unless its very recently from when I last drove it, it wants to almost die.  If I keep the revs up or rev it too about 4-5k a couple of times then it seems to be ok once I get moving.  It won't happen again until I park the car and come back later so its not that big of an issue but I hate sounding like a jackass every time I start the car because I have to rev it up.  And when I try to go its like it wont get gas for a minute but then kicks in about the time I get out of the parking lot and is good for the rest of the ride.  I will say that since I have just about run out all of that old gas (plus a half tank of premium) the cars has seemed to smooth out and pull stronger.

Any idea what could be causing this and the CEL?

[DesktopDave]

I'd try a stomp test to see what the CEL is.  Might just be an O2 sensor or something like that.  Would you say the problem happens only on cold starts?   If so, I'd be betting on one of the temp sensors being out of range.

[Wrench]

Junk gas was making my CEL come on while driving. If I released the throttle it would go out. I pulled codes and it had an O2 sensor control code. It hasn't done it since I filled up with high test gasoline.

Like Dave says, pull he codes and let us know what shows up.

[willworkfore30s]

Ok, I did the stomp test but I got some crazy numbers.  They came out as follows (I did it a couple of times to make sure):

1224 / 1(long)122 / 41(long)12 / 241(long)l / 2241(long) / 1224

1224 is coolant temp sensor which makes since because I saw that the shielding had come of the wire in a spot and knew it would soon need attention.

After looking at my numbers closer, I think that the 1(longs) are to signify the end of that code and the start of a new one.  If that is the case then the only code it is throwing is 1224.  Can anyone confirm that this is the case?

[DesktopDave]

I'm pretty sure the long pause is for the code repeat.  I don't recall a single flash on mine, but it's likely.  The DME will loop codes until you turn off the key, so that 1224 must be your only code.

I'm betting you're right about the harness.  I'd splice it, maybe use a bit of that paint-on insulation and/or fabric friction tape...then disconnect the harness from the DME and do a resistance or continuity test on the coolant temp sensor wires to the DME plug pins.  Don't do either test while the DME is plugged in...the multimeter puts out enough voltage to damage solid-state electronics!

I'd also recommend testing the resistance on that CTS while you're at it.  I don't recall the exact numbers, but it should be pretty high when it's cold, like thousands of ohms & drop substantially as it heats up, like down to only a few hundred ohms.  Some BMWs might have a resistor soldered in-line as well, it was a fix for rough cold-starts on early Motronics.

[willworkfore30s]

Thanks for the info.  I'll make the repaire and report back on how it turns out.