Hunting problem!revs going up and down when idling! Golf MK4

[Colin1882]

Hello All,

This is my first post and i'm a bit of a novice with car's so any help is more than appreciated,

I have just brought a Mark 4 Golf and love it but it has a Hunting problem where the Revs go up and down intermittently when idling! it sometimes cut's out when i slow down and turn at an angle into my driveway and takes a good few times to start again? i have had it serviced and a few things came up when it was scanned:-

1.Fuel system is too lean
2.Catalytic system efficiency below threshold
3.EGR system excessive flow

Also the Temperature Gauge was only working intermittently!

A week after the service a warning light came up saying "Emissions Workshop"

I took it to the garage and had the Temperature sensor changed and the warning light cleared and the gauge was now working fine but the Hunting problem is still there???

I have read that it could be a lot of things like, Air intake manifold, dirty throttle bodies, MAF sensor, inlet manifold rubber seals, idle sensor, unmetered air, lambda sensor, coil pack, EGR valve, breather tube, wiring loom to coil packs, software updates from VW.

Would the 3 problems that came up on the machine point to one specific problem or area?

Thanks for your help in advance!

[Dr G]

First things first; clean throttle body (carb cleaner) & look for air leaks. Easiest, most common and virtually free.

Grammar nazi: you just bought it

[Colin1882]

Thanks Dr G

I will give that a try and hopefully that will cure the idling problem!

Just ordered some carb cleaner.

Cheers

[Sticks.]

FWIW I had exactly the same many years back on a 205 cti and cleaning the throttle body improved it a lot. Crud was being drawin into it as the crank case vent was upstream. Engine tried to stall, ECU sensed this, raised the revs momentarily and so on....

Not sure if yours is similar, but taking out the air bypass screw, cleaning it and putting it back helped too - even if it looked only slightly dirty. Screw it inwards fully first, counting the turns so you can reset it more easily.

[MagicBoyUK]

Which engine?

I had similar problems with a Bora 1.6 a few years back, also intermittently cut out when slowing on motorway off-slip. Turned out to be the crank position sensor after a master tech checked it. The host of other errors tripped because the timing was out.

[Colin1882]

I am happy to report that it was only a dirty throttle body, brought a can of wynns air intake and carb cleaner (£4.29 from Wilco) and didn't even need to take the throttle body off! sprayed quite a lot in probably about 10 times as i held it open and cleaned with an old toothbrush as i went along. Gave it about 20 minutes to dry out a bit and tryed to start the engine, it took 3 times to start, revved the engine a lot and so much white smoke and rubbish came out the exhaust.....was a bit worried because the problem seemed worse than before and 3 warning lights and workshop message came on and stayed on! they were EPC, the exhaust sign, a triangular sign with a circle round it and engine workshop! i put the engine cover back on and took it for a drive and it seemed to run so much better but the idling problem was still erratic(worse than before) then after about 15 minutes of driving i pulled up and stopped and idled the car and it was perfect and seemed to have sorted itself out and the EPC, triangular sign and workshop message went out and i could feel it was a lot better. I turned it off for 10 minutes, started it again and all is fine and when i was pulling up to traffic lights etc it was idling perfectly, i took it to a local garage before with this problem and they didn't have a clue and didn't know where to start..... they could of changed a lot of sensors etc and charged me a lot for them and labour costs and all it cost me was £4.29 and a bit of my time..........the exhaust light did still stay on though but i knew i could get rid of that by just taking the negative terminal off the battery for about a minute, i reconnected it and after starting the engine all warning lights now go off and the car is running and idling perfectly! Hope this can help someone else as this problem is really frustrating!Thanks for all your reply's!

[Fireflyguy65]

Hi bud,my car has the very same issue,i have literaly just change my egr valve,reset and car idled as it should,the second i pull out to drive test my car,i had engine check and epc light,and emmisions came up on screen,engine came up on screen,i have the yellow circle with the ! mark in it...previously i have changed both o2 sensor,and pre cat sensor....i cleaned out my throttle body,and i am still getting the P0106 coming up on my obd device....i am at a loss now,i know alot about engines but I'm oldskool,so haven't a clue about electrical systems... I'm glad you sorted yours out...😊👍