Newbie with idling problem

[JamesDaniel80]

Hi,

I know it's been discussed many times before but I've tried just about everything to stop my engine surging but without success.

I'm the proud owner of a MK1B which I've had for about four years, three of which have been spent in the garage.

I'm in the process of getting it back on the road but it's developed an annoying issue where it won't stop surging on idle.

The symptoms:

It starts fine and for about a minute or so, the idle speed is steady at the fast idle speed as the engine warms up.

Then the surging starts...It just goes up and down, up and down.

Eventually the fast idle will cut out and the revs will drop as you would expect, but even though the revs have dropped, it still surges.


What have I tried?:

I've bled the coolant and I know there is no air in there.

I've also changed the coolant temperature sensor and cold start sensor.

I've changed the MAP sensor.

I've checked for vacuum leaks and I'm pretty confident that there are none.

I've checked the TPS which is working fine.

I'm running out of ideas!!! Can anyone help?

Thank you in advance,

James

[PW@Woodsport]

Pretty simple really, your waxstat or AAV is not closing properly OR you have an airleak somewhere on the plenum/intake/throttle body.

Easy test.... remove the air intake pipe from the throttle body, locate the AAV bypass hole and place your finger over it with the engine running, it's 5p sized at 5 o'clock position inside the throttle.

If the engine stalls or revs drop right down when you do this then the waxstat is not closing properly.

The cure is either a new waxstat or manual choke conversion.

[JamesDaniel80]

Thank you very much. I'll have a look at that tomorrow.

How easy is it to do a manual choke conversion?

[scomr2]

Manual choke is pretty easy - worst bit is getting the wiring from the valve to a switch on the dashboard.

A mk2 a/c idle up valve works ok on mine.

Simon.

[JamesDaniel80]

Well I've tried about everything else...and getting a new waxstat valve looks pretty difficult (and a second hand one looks like a bit of a minefield) so I've ordered the kit.

Thanks for the advice!

James

[PW@Woodsport]

Thankyou for the order James, i wasn't angling for a sale, just handing out advice to a well known issue, although if the AAV is sticking the manual choke will fix the problem.

You will get it by Thursday at the latest, thanks Paul.

[LimeyMk1]

Manual choke is pretty easy - worst bit is getting the wiring from the valve to a switch on the dashboard.

A mk2 a/c idle up valve works ok on mine.

Simon.

Wiring isn't too bad, there's a free 12v source in the footwell fuse box which will take a spade connector. Stick an inline fuse on it then up to the dash switch (get an iluminated one). Then a single wire to the solenoid and then to ground on the rear firewall.

Is that what you have in the destructions Paul?

[PW@Woodsport]

No my kit is permanently live with a switched ground, same thing though, it would work either way.

There is a guide written by me that Jimi posted on the OC showing how to make your own manual choke.

[jimi]

Pretty simple really, your waxstat or AAV is not closing properly OR you have an airleak somewhere on the plenum/intake/throttle body.

Easy test.... remove the air intake pipe from the throttle body, locate the AAV bypass hole and place your finger over it with the engine running, it's 5p sized at 5 o'clock position inside the throttle.

If the engine stalls or revs drop right down when you do this then the waxstat is not closing properly.

The cure is either a new waxstat or manual choke conversion.

same answer I posted to the same question on the OC

Manual choke is pretty easy - worst bit is getting the wiring from the valve to a switch on the dashboard.

That's easy you have unused cruise control wiring that runs from the boot (LHS behind the trim) to the dashboard almost exactly where the coinholder is
Details of the wiring here http://jlawson.co.uk/originalsite/Vario ... iring.html

Paul's article on the manual choke is here:

https://mr2oc.co.uk/know-your-2/mk1/mk1 ... rsion.html
and the instructions to build your own

https://mr2oc.co.uk/know-your-2/mk1/mk1 ... tions.html
and an article of mine with a timer controlled version of Paul's choke

https://mr2oc.co.uk/know-your-2/mk1/mk1 ... kbartid=56

[JamesDaniel80]

Thank you very much for your advice, everyone.

Having done the test of the waxstat and AAV as recommended by Jimi, it turns out it is that which is causing my problem!

You've saved me hours of messing about with hoses and wires.

Hopefully once the manual choke conversion is installed, it'll be plain sailing!

Thanks again!