348/Mondial T just not running perfect....

I have an Euro '89 Mondial t, with the Motronic 2.5 and no cats.

A couple of days ago it started just not running as perfectly as it does.

See before, if I went into 3 or 4th at 1000 rpm (it is a test, not the regular shifts which I'll do at 5K rpm +) I'd get a deep rumble from the left intake (inlet) and the car would just slowly accelerate without a hiccup and dead smooth and progressively.

Now, it kind of feels rough, as if occasionally missing a bit, a slight arrhythmia, a slight vibration and lacking the usual smoothness. When starting from first, there is an ever so slight hesitation until the RPMs creep up then I guess it smooths out by virtue of the higher rotations.

MAFs are set to 343 Ohms (383 were just too lean when we stuck it on a Dyno, 343 give us the CO and HC parameters as speccd in the operations manual). If I disconnect each spark plug in turn the engine does run rough, so the sparks are OK (checked each one and they are all slightly grey, heat on the middle of strap etc). The same goes for the injectors, though when 1 and 4 are disconnected the engine runs rough but with a more clankety-clank than the wrof-wrof-wrof that it does with the 2,3 and 5-7 injectors.

Idles at 1000 on the line, exhaust hums with no pops or anything else.

Charging system works just fine,a all electrics work

K&N filter put in 4 months ago. Car used for 5,000 miles over the winter and used every day. Last major was last September with belts 2 years ago...

So what am I missing?

 

Thanks guys. The MAFs are clean (I cleaned them with the Q tip and brake oil). I went as far as replacing them with a spare one to see if it made a difference - none. The burn off is quite efficient, especially to burn off hydrocarbons like the light oil of the KN's. I have a Montronic 2.5 engine, so only have a throttle position switch - Idle, partial and WOT. This works fine with all three positions represented reliably.

P.S. if you have an F-up'd MAF with broken wires, let me know. I can resolder the circuit board to another body and repair them for less than $ 100 - just to let you all know...

Thanks again. It seems to be getting better the more Optimax I dilute the Esso fill-up with. Hopefully it will just be a bad batch of fuel - I'm doing a long drive to Paris, and either I'll have a happy flushed Mondial T, or it will be on a flatbed back...

 

Yup, I'm targeting the Crank Position Sensor this weekend for good preventative measure. I'm going to remove the connectors altogether and solder them directly with shrinkwrap. That should eliminate the whole connector issue ever again. If I need to replace them, I can just cut the wires and resolder a new set.

Regardless, it is now running almost completely normal. I'm filling hr up with Opti tomorrow...

Thanks to all,

Marco