Gti Running Rough - Very Poor Idle

[mattmk1 0]

Right slowly a few problems with the way the steelie runs have arisen, i think its down to a combination of things, but if anyone can shed some light/advice id be very grateful.

 

 

1. When very cold - as in just started, the car is violently fast, but the further you travel the more power it loses. If you thrash it it goes well, but its just no wehere near as responsive or freee reving as when cold.

 

2. I noticed the throttle position sensor was unplugged yesterday - its probably been like this for a few weeks - and reconnected it. Since then the car has a very erratic idle. When cold tickover is 13-1400 rpm, when warm it settles to 1k rpm. However when u slow down to a standstill and drop it through the gears as you slow, the revs dip to 500 rpm or so as you dip the clutch. Today it must have cut out at least 20 times as when you dip the clutch in 1st and coast the car cuts out.

 

If you put it in 1st dip the clutch and blip the throttle as you brake, the idle returns to 1k rpm ish and idles nicely as you sit in traffic etc.

 

3. Not a massive point but the fuel consumptions very erratic. The last few lots ive put in are as follows :

£15 of bp ultimate - 75 miles

£15 of ultimate - 62 miles

£30 - 210 miles - worked out to 29.5 mpg -very pleased

£25 - 182 miles

 

I commute 6 miles or so and the car sits in traffic an awful lot so im pretty pleased with the fuel consumption, but would you class the usage as erratic?

 

Anyway, if anyones got any thoughts then fire away, the cars a 92 1.6 no cat or anything, standard apart from a K&N.

 

cheers

matt

[Pug_101 0]

Try checking for a air leak on the intake side.

Make sure the throttle possition sensor is adjusted correctly. This is covered in Haynes manual, but basically it should click as soon as the throttle starts opening.

Check all sensor connectors are clean and fit well.

 

Try the above first and let us know if theres any improvement. Don't think K&N be helping (car running lean) how was car before fitting it?

Cheers

[Rob_the_Sparky 9]

LOL, I can't believe the bodges that go on to fix a dodgy idle, disconnecting the throttle pot is a new one and bodging at new heights! The reason for hte lack of power is that on WOT (Wide Open Throttle) the throttle pot enriches the mixture to give full power. The ECU temp sensor does a similar thing to a cold engine (but lots of throttle on a cold engine is a bad thing for engine life).

 

Try a search on idle but the basics are:

 

Check for air leaks

Check the ignition timing

Adjust the idle mixture (on the AFM)

Clean/clear the breather pipes

Cleaning/re-tracking the AFM

Clean the throttle body

 

Roughly in order of how I'd do them

 

Rob

 

P.S. the SAD keeps the revs up but on almost every car I've had it closes early leading to a period of questionable idle. Once the idle improves though it should stop cutting out.

 

P.P.S. I hope you take it for a decent run every so often, 6 miles of stop/start traffic is not great for engine health as the engine never gets properly warm (oil temps in particular).

[mattmk1 0]

LOL, I can't believe the bodges that go on to fix a dodgy idle, disconnecting the throttle pot is a new one and bodging at new heights! The reason for hte lack of power is that on WOT (Wide Open Throttle) the throttle pot enriches the mixture to give full power.

 

Woah hang on a minute, i didnt disconnect the throttle pot on purpose, im not that much of a bodge artist The metal clip which holds the sensor on had come off and consequently the the sensor had become unclipped, i reattached it as soon as i noticed it was lose. It was just an observation that i didnt have the idle issues with the sensor disconnected. Reconnecting the sensor also has made no difference to the power - if anything it is even more down on power.

 

Fitting the K&N hasnt altered the idle at all, it just seems to have smoothed out the power delivery and made it a little less jerky in traffic.

 

Ive already checked for air leaks and theres no sign,

I adjusted the timing slightly last nigh and quickened the idle slightly so that it will run without cutting out. However it now idles fast when cold 1400 rpm ish but it settles to 1000 rpm when hot.

 

At the weekend im having a bash at checking the timing with a timing light. And also checking the advancce is working correctly.

 

 

And yes it goes for a good blow out at least twice a week, i come home down all the twistys whenever the weather allows etc. However im reluctant to rev it above 3k at the minute as something is obviously not quite right.

 

cheers for the suggestions,

any other ideas?

thanks

matt

[Pug_101 0]

Fitting the K&N hasnt altered the idle at all, it just seems to have smoothed out the power delivery and made it a little less jerky in traffic.

 

How is the K&N fitted? in the same place as the normal airbox, ie over the exhaust. If so the hot air could effect the top end power without it being sheilded from the heat and a good cold air supply provided.

If better flowing is achieved in an engine the fueling should be altered to match, some system automatically compensate for this and some don't. I am not sure of your system, but i would say the fact you don't have a catalyst and therefore no air/fuel mixture sensor your mixture could be out. How much difference this will make to your main problems I can not be sure as every car will react differently.

If I am not mistaken the AFM adjustment screw will only effect the idle mixture.

Cheers

[mattmk1 0]

The K&N is mounted in the front corner of the bay in front of the battery, with the cold air feed tube hidden underneath the valance and blowing directly onto the filter. Im not sure wether i can adjust the mixture - i think i can via the throttle body, its running bosch ignition if its any help!

[Pug_101 0]

The K&N is mounted in the front corner of the bay in front of the battery, with the cold air feed tube hidden underneath the valance and blowing directly onto the filter. Im not sure wether i can adjust the mixture - i think i can via the throttle body, its running bosch ignition if its any help!

 

This means the AFM has been moved and is now on it's side. correct?

Are the connectors to the AFM facing upwards or downwards. Anyone know if one way work better than the other?

Is it possible to change things back to a standard setup including all breathers and sad connection etc it far easier to problem solve that way.

[mattmk1 0]

Yes the afm now sits at id guess a 30 or 40 degree angle on its side with the connectors facing down. I do have all the standard parts available but the problem is still there with the standard equipment in place. I wouldnt have thought fitting a easier breathing filter would cause the idle to decrease and stall, in fact id have imagined the freeer flowing filter to quicken the idle slightly.

 

Im guessing i have a problem with my throttle position sensor as the stalling problem has only arisen since i reconnected it. Before this the car just seemed down on power, now it is both down on power even more so and idles roughly.

[Rob_the_Sparky 9]

Having the AFM at a slight angle will in theory make a difference but the jury is out on how much. Not convinced it will make much difference.

 

Poor idle like yours is generally down to retarded ignition timing and/or rich idle mixture. A retarded ignition will also make the engine feel a bit flat but you seem to be describing something worse than this. Ignition is commonly retarded to make them run on 95RON although I believe it is less of a problem on a 1.6 than a 1.9.

 

The throttle pot is actually just a couple of switches. One for idle and one for WOT, it alters fuel mixture and idle switch can make things worse if idle is already poor. Not sure why but it is common to adjust the idle switch so that it never turns on to improve the idle but it is not necessary if the underlying problem is fixed.

 

The AFM mixture screw alters only the idle mixture.

 

1400 idle dropping to 1k when warm is about right, the SAD is a pretty primative device. Enough to make it run at cold but by not good at controlling revs!

 

Good luck

 

Rob

 

P.S. Does the top of the ECU look right or more like it has been opened and then sealed down again? It is common to open them up to adjust idle problems but this can effect power across the range if not done carefully.