Sons mk 4 golf has just started dropping revs when coming to a stop (when completly lifting the throttle). Revs will drop momentarily to about 400revs, then it corrects itself to about 800 at idle. Idles fine on start up, but after an increase in revs and returning to idle it drops to almost stall for a very brief time. It's manual and other than that it runs perfectly fine. Any ideas where to look? Throttle cables and fittings are all good and smooth.
franc123,
Jul 21, 1:05pm
Give the throttle body a clean out. Also check for any induction leaks, VW's are intended to be recycled after 7-10years and the quality of plastic and rubber hoses, pipework etc reflects that. They're shockers for splitting or in the case of rubber parts, actually dissolving, worse if it's a used Asian import and been subject to high underbonnet temperatures.
msigg,
Jul 21, 6:01pm
Yes as above, spend some money on it, give it a good service, clean the throttle body, give it some plugs and air cleaner, some nice oil,check all connections ,electrical and hoses etc, put some nice petrol in it and give it a nice long run.
trackim,
Jul 21, 6:10pm
Cheers Car is very well serviced, has a 100km run every week day. Plugs not old, we only run top oil and high octane fuel and aircleaner is in tip top condition. Will check hoses etc for air leaks. Thanks for the info.
meow_mix,
Jul 21, 6:29pm
I had this problem on my car, sometimes the idle would go so low it would cut out. Turns out the idle stepper motor needed cleaned which I had done by a garage. They also adjusted a setting on the engine which raised the idle up a little bit.
devil99,
Jul 22, 1:20pm
have a garage check fuel trim info to see whats going on
jmma,
Jul 22, 3:46pm
Wonders why someone hasn't come in with 10 or more paragraphs on how to fix this? I'm a Toyota man so can't help you OP :o)
gunhand,
Jul 26, 7:41pm
The tumble weeds certainly do blow through threads like these, odd isn't it.
intrade,
Jul 26, 7:49pm
the problem is most these new cars are quite complex from wrong service to neglect all matters . you really need to hook it up to rosstech vcds or odis as the first thing and know if it had correct fluids and was run at 95 ron minimum and not on ethanol fuel. I would have to write a whole book . cleaning the iac and a relearn if fueltrims are both lt and st are below 10% correwction 6 and above `corection from 0 is a problem channel 032 and 033 for fuel trims
An update. By the way intrade, a mkIV is not a new car - it's 17 years old! As said earlier, it's very well maintain and only runs the correct oils etc. Please don't assume all people posting in here are not at all tech and mechanically savy. Back to update. All hoses/lines, connections all checked for cracks or leaks, throttle body disasimbled check and cleaned. Have found though that if air conditioning on, it runs as normal - no big drop in revs when throttle lifted. Air con off, and it almost drops to stall momentarily before correcting it's self. Anyway, off to the garage today to let our local pro look at it.
supernova2,
Jul 27, 9:44am
My bet is a problem with the IAC (idle control). The A/C will usually pull the IAC up a bit to account for the exta load. So is there also a adjustable idle speed stop? If so maybe it needs a bit of a nudge.
trackim,
Nov 11, 9:13pm
Yep, all fix. Indeed it required an idle control reset. Thanks for all the advice.
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