engine bucking at 2000 refs

Dear friends
my Punto Sporting MK1 1998 is having a strange problem. When i drive in my town, were we have a speedlimit of 30 km/h, i drive at 2000 refs/m
in second gear and than its if the engine has a problem with the fuel cut off system. I don't do anything with the throttle, but the car starts bucking like it is short of fuel. When you make more revs, say 2500 the problem is over.This problem has shown in all the gears round 2000 refs/m. I know that the fuel cutoffsystem comes in when you take your foot of the throttle and gives fuel at 2000 refs/m. I think the problem is due to that fuelcutoffsystem. Although someone told me it could be, that the throttlevelvehousing is dirty. Has anybody an answer for this problem?
greetings Nico
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Look at my post in this group about ECU conditioning. (Date within last 30 days)
Nick /////

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Nick,
my provider has removed all postings, that were posted before the first of october, so i have not read your posting about the ECU conditioning.
Nico

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Totally remove the throttle cable so the throttle can be freely rotated by hand.
Gently move end stop to end stop (especially at the nearly closed end) feeling for any drag, snatching etc.
The other possible cause is that the ECU which is self adaptive has got itself all confused and needs retraining.
The sequence (from memory) is as follows:
1) Disconnect battery for 30 minutes 2) Reconnect bat. 3) Start car and allow to idle till fan cuts in 3 times 4) Rev car at a steady 3000 rpm for five minutes 5) Release throttle and allow engine to idle for 1 or 2 minutes 6) Switch off
Please report back how you get on.
Nick /////

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Nick,
it may take a while before i report back, because my mother in law is in hospital, and until she is out of the hospital, we need the car. But i wil report back!
greetings Nico

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Initially for your case you can skip the throttle cable removal and manual operation of the throttle plate. Go straight in at step 1. Only 30 minutes down time. Reading the info again I should add that step 3) starts with a cold engine so steps 1 & 2 can be done overnight. Steps 3 to 6 could take up to 30 minutes.
Nick /////

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Nick i have followed your instructions, and it looks very prommissing, because i have driven for a few miles now at 2000 refs. and the engine responded normaly on the throttle and the engine didn't buck at all. The only thing i want to try now is drive a few miles, when the engine is cold again.(because with a cold engine, it was the worst) I'll report back again then. For now: thank you, o great Fiat wizzard.
greetings Nico

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Nick
i have driven with the car this afternoon (starting off with a cold engine). I must say the car is much better now, although he bucks a little (when the engine is cold), but not as much as before, because before i had to push down the clutch to stop the car from bucking. That is completely over now. I hope it stays this way.
greetings Nico

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Well when you get time you can unhitch the throttle cable and check for the smooth operation of the throttle plate. Also a gentle air clean of the idle solenoid actuator followed by a quick squirt of WD40/other light oil won't go amis. Also a little WD40 around the throttle plate spindle can only help improve matters.
Reasoning: With active mechanical idle control onto the throttle plate linkages (as opposed to air bypass methods) then any snatching will result in the actuator pushing harder to overcome excessive stiction and then when overcome will go into overdrive resulting in rapid backoff and so the cyle repeats.
I need not add that clean air filters and spark plugs in good condition help to reduce other air/fuel combustion problems that could otherwise add to the problems of other systems.
Nick /////

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I will check the smooth operation of the throttle plate, in the near future. My car gets a check up every year at my local Fiat dealer, and than the sparkplugs are replaced and the airfilter also if necessary. Thank you for the information and explanation.
Nico

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