Mk4 Golf, rough idle and sucking in gunk

21 Nov 2014
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United Kingdom
Hey people,

Just as soon as I've got rid of one car and got another, I've got a problem with it again!

It's a mk4 Golf, 2001 1.6L 16v. 110K on the clock

I bought it from a dealer just over a week ago and it was taken in part exchange so I got a fairly good deal on it.

It looked in decent nick and drove quite nicely on the test drive, it has got all matching Firestone tyres throughout too, even the spare so I thought this was a good inclination that the previous two keeper had looked after it, along with all the service history.

Anyway, when I got the car I gave it a bit of a service like I always do when I get a new motor, the oil had just been changed on so I put a new air filter in, replaced the spark plugs, put some oil additive in along with some fuel additive to help clean the old girl out.

I also took the throttle body off to give it a good clean because the revs were jumping up and down a touch when idling. done this in my old mk3 Golf and it sorted it out.
The underneath of the throttle body was absolutely caked in ****, a black greasy soot, I've never actually seen anything like it and took a good while to clean it out. inside the intake manifold looked like it had a lot of crud in there too.

Anyway, I cleaned the throttle body and what I could of the intake (without stripping it down) and put it all back together.

The revs are still bouncing up and down on idle and it seems to me like it doesn't have as much power as it should, it also seems like the speedo is out. I've tested it against a satnav and two phones which were all reading the same speed. so when I was doing 90 in my car (which really didn't feel like 90) it was actually 70mph. quite a difference!

I took the engine cover off of the top of the engine which houses the airfilter and has a breather pipe thing going into the box too.

The breather pipe was/is covered in gooey mayo grease. not a good sign anywhere if you ask me.

The came with a 30 day warrenty so I took it back to the garage where I bought it from, they said I would have to leave it with them. later that day, the sales man/receptionist (nob head) told me that the engineer couldn't find anything wrong with it, had plugged it into diagnostics and found no faults but did admit that it didn't seem right.

I'm thinking that they either couldn't actually be bothered to look at it properly or they found a big fault and didn't want to fix it because it would have to be done for free. Maybe not, I just got that sort of vibe from them...

Does anyone out there know what could be wrong with it?
I've got a feeling that it's sucking in a load of **** and cant sustain combustion properly so injects a bit more fuel in to compensate, hence the bouncy rev counter at idle...

The car is alos fine once started up but gets worse at running temp. I've also driven it without the airbox on for a short distance and the idle seemed to handle it a bit better..

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I really doubt if the garage would bother, but it would be a good move to remove the rocker cover and clean out all of the crap that will certainly be there.
Usually there are mesh screens covering the breather hose outlets and they will be grotty too.
Blow all the rubber breather hoses out with compressed air - there will be water present - and there will likely be hoses from the rocker cover and crankcase.
After that, its a thorough clean of the throttle body and idle control valve, plus a new air filter.
Believe me, the garage will have done the minimum to the car pre sale.
John :)
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It would be beneficial to check all the breather pipes and clean out if necessary, probably years of build up.

What was said above clean all pipes on breather system
Lots of short journeys can do this
Cleaned out the crankcase breather pipe but not had the crankcase breather box off to clean it. anyway. I've just done a 130 mile round trip and there's now no gunk coming from the breather pipe (for now anyway) but the cars idle is still jumping from about 600 to 800 rpm continuously.
I plugged my little diagnostics reader in and it's giving me a code of 17962 which translates to - Idle Speed Contr.Throttle Pos. Basic Setting Conditions not met

Any ideas on what that actually means?
This is very similar to a thread that has been running for some time now?

Carburetor cleaner into the throttle position sensor, see does things improve? The older ones had a switch to tell the ECU when to idle. Contacts get dirty.

If in doubt vent the sump to the outside ..........
Ok, so here's the update...

I cleaned out the MAP sensor and EGR sensor along with the throttle body again. Put it all back together and it was driving nice and the revs weren't bouncing around at idle (or at least that I could notice)

I done a 300 mile round trip over xmas and now the rev counter was back to normal bouncing from 600 to 800rpm over and over at idle. But my little diagnostics reader isn't reading any faults.

I've just taken the throttle body off and it's caked in black soot again, which I think is coming from the Exhaust Gas Recirculation. I've cleaned the throttle body right up again, checked the MAP sensor and it's all clean.

The breather pipe is now not an issue. no gunk in there whatsoever, so that is good news at least. Think it just needed a clean out and a couple of long journeys.

I'm going to re-assemble the throttle body and leave the EGR unplugged for a few days and see how it gets on.

Just a bit concerned that my engine could be burning a lot of oil, but then if the intake manifold is dirty it will burn the crap that's in the manifold and then re-circulate some of that crap back into the manifold....

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