Hi mate, did you find a result to fix it? i've just bought a 1.4 mk3 and ive got the exact same
problem, ive taken it to 2 different garages, one just changed some codes and the other said it was the egr valve that was blocked up and he'd cleared that but 5 mins driving it down the road the epc and engine management light comes on. also theres no pickup in the acceleration like the revs are high but even if i have my foot to the floor, the speed only crawls up and this is all from 1st gear to 2nd and 3rd. before i had a 1L 60hp kia picanto and that wee badboy had more kick about it than this, if anyone has any advice, you're all very much welcome!
I did actually solve the
problem but forgot to update the thread, my apologies. Turns out the issue was a dirty MAP-sensor.
I initially suspected the throttle body or gas pedal was the main culprit since it kept throwing up throttle body and gas pedal related codes. Since I got the car last year I would also occasionally get a P0106 code relating to the MAP sensor as well as the EPC light when driving, it would happen when I shifted from 4th to 5th gear and I lifted the clutch pedal too quickly, I didn't think these problems were related but I decided to investigate the MAP-sensor first as it tends to cause many idling and engine related problems. I removed the MAP sensor to take a look and it turns out that the MAP-sensor was completely covered in soot and carbon build up over the last 20 years or so which caused interference. I sprayed it with some electronic parts cleaner and the issue went away almost immediately, it took a few minutes of driving and couple engine restarts for the symptoms to completely disappear and they've not come back since. I did notice a slight improvement when accelerating as the car didn't surge and hesitate anymore when applying full throttle when joining the highway for instance like it did before and the idle feels a tad bit smoother as well.
Since the sensor was almost 20 years old I did replace it around a week later with a new BOSCH sensor since they only cost around 35$ on Autodoc. The new sensor has a different part number and a slightly different look compared to the old one as well (new 0 261 230 234 old 0 261 230 095) so likely this is an updated part, didn't notice any performance difference with the new one though so I believe the previous one was working fine once cleaned but I replaced it anyways.
I did remove the MAP-sensor quite recently to check for carbon build up and to my surprise there was none, it looked exactly like I had just installed out of the box so it seems that carbon build up isn't an acute issue, considering the low mileage this car has for the age it was probably not driven very hard where the engine reached operating temperature, probably city-driven for most of it's life which caused this. I use this car for commuting on mostly highways so carbon and soot will probably not be an issue (hopefully).
Since the MAP-sensor was completely covered in gunk I thought it's fair to assume that the rest of the intake manifold, throttle body, EGR and PCV system is also covered with the same stuff so I initially thought about removing everything and giving it a thorough cleaning but since the car is almost 20 years old I decided against it since removing all of it is quite an involved job and replacing broken and brittle plastic components would be a major hassle, especially the intake manifold. I ended up just cleaning the throttle body.
The throttle body was completely covered in caked-on carbon deposits, I tried to use various solvents and degreasers like brake cleaner, electronic parts cleaner, acetone, white spirit and even oven degreaser to no avail. The carbon had basically solidified on the surface and it was essentially flaking off, I ended up just using a wooden tooth pick to scrape off as much carbon as possible, primarily around the edge of the butterfly valve where it contacts the housing and the shiny coated surface around the valve. I reinstalled it on the car and the engine was throwing all sorts of codes and the idle was all over the place, so I readapted it with VCDS. The idle is now almost buttery smooth and I feel a slightly better response from the engine when driving.
These are pictures of the throttle body after cleaning it, forgot to take before pictures. As you can tell I didn't bother making it sparkly clean, only the coated shiny surface and the edge of the valve.
Looking at the way the EGR pipe is pointed upwards, no wonder the back of throttle body was covered with rock hard deposits. Brilliant design.
