Mk2 8V GTi Digifant running problems

[Ians3422]

Car is a '91 GTi 8V with 166k on the clock. I was given the car last year after it suffered a battery earth fault which sent the ECU faulty & flooded the whole engine with petrol. I got her up & running last year (with help from Crasher on the old VW forum - cheers mate!) and she's perfectly drivable but ive still got a couple of problems to iron out:

1) ECU - the original ecu number ended '022 DB' but at the time I could only get an '022 N'. It ran fine but I was told the '022 DB' ECU would run smoother as it's a later version. I managed to source one and swapped em over & she ran better, but had a problem that when coming off the throttle the revs would quite often stick at about 1600rpm; you had to 'blip' the throttle in neutral to bring the revs down to idle. Thought it was a mechanical problem (sticking throttle cable) but it was'nt, so the 'DB' ECU was discarded & replaced with the 'N' unit - until last week when I got hold of another 'DB' unit.
Fitted it at the weekend and it's doing exactly the same as the other DB ECU!!!!!! Can anyone help with a possible cause??? Does the Digifant management have a diagnostics port as my brother has a fault code reader he uses for his mk3 8V Gti?

2) If the engine is driven for a while (10 miles or so until properly warmed up) then stopped for a few minutes (to get petrol), when restarted it revs at about 1800-2000rpm and wont drop to idle for quite a few seconds, anyone seen this before? This happened with N type ECU - havent tried it with the new DB ECU yet.

3) Am gonna change the timing belt soon & set the timing, does anyone know how to test the Knock sensor? Is there anything else I should check & how? Haynes manual says the timing should be set at 2000-2500rpm, when the dizzy should be turned until the pointer on the flywheel/ bellhousing lines up. I was gonna set the timing at 2250rpm, is this right? Haynes also says to check the Hall sender & blue temp sender, although I changed the temp sender last year & am assuming car wouldnt run with a faulty Hall sender?

4) Gearbox - ive seen a low mileage gearbox for sale from an older EV engined Jetronic GTi 8V - it looks like an 020 type, will it fit my PB engined car and will the ratios be the same?

Any advice from your previous experiences greatly welcome!

[Diamond Hell]

1)clean the throttle butterfly with carb cleaner and a paint brush - this sounds like it might be mucky, which can stop it closing, causing odd idling problems. You might also like to check for vacuum leaks with an unlit blowtorch - if it's near a leak then the gas will get sucked in and the engine will race.
2)see point 1)
3)pass
4)It'll fit, but the ratios might be different.

[Ians3422]

Cheers mate, will try cleaning the throttle butterfly. Can I do this without removing the throttle body from the car?

I changed all-but-one of the vacuum hoses previous as they were all original, 17-ish years old & getting brittle. Have even changed the seal on the EGR pressure regulator (where it fits into the top of the rocker cover) - this cost a fiver but made a heck of a difference to the idling (dont matter how fast its idling it'll do it without hunting up & down). Theres one more vacuum hose to change (a tiny little sucker behind the throttle body & right up against the bulkhead - just need someone with skinny hands to get at it; i've already asked the wife - no chance!!!!) but this hose 'seems' in ok condition, just a few frays to the outer braiding.

I like your idea about testing the hoses with gas, will try it out! Someone else suggested doing the same with WD40 (its supposed to 'plug' any leaks and make the engine race), will try your idea first as it's cleaner.
Have also changed the Idle stabilisation valve but this didnt do nowt.

Will let you know the outcome!