need help real quick

[hippy]

i went to test drive this diahatsu charade and if it weren't for this problem i would of bought it then and there.

the engine on idle seems to lose revs and then picks up again, like if its running out of puff .... he said that this only started to happen after he had the engine washed out ... the engine was really clean looking, it was a good clean, looked good as new but the engine wasn't smooth at idle. it would never cut out, just keep on loosing its revs and pick up again every couple of seconds. so something must have got wet during the wash. he asked the guy who washed it and they said to give it a bit of time for it to work itself out??

what do u guys think it is? 94 model daihatsu

thanks